U b j D O ' J l & M DEVELOPMENT OF HIGH PERFORMANCE AUTOMATIC VOLTAGE STABLIZER FOR TELECOMMUNICATION APPLICATIONS A dissertation submitted to the Department of Electrical Engineering, University of Moratuwa in partial fulfillment of the requirements for the Degree of Master of Science by: SHYAM SANDARUWAN KAWSHALYA THOTAGAMUWAGE L IBRARY UNIVERSITY CF MORATUWA, SRI LANKA feiGHATU'.VA Supervised by: DR J.P. KARUNADASA University of Moratuwa 9 2 9 7 1 , vN r ' X >1 bJI. 3 o<5 Department of Electrical Engineering, University of Moratuwa, Sri Lanka. December 2008 / c ^ 9 2 9 7 1 DECLARATION I certify that the work submitted in this dissertation is the result of my own investigation, except where otherwise stated. It has not already been accepted for any degree, and is also not being concurrently submitted for any other degree. S.: w ge 22-12-2008 I endorse the declaration by the candidate. DR J.P. Karunadasa Supervisor ABSTRACT The Telecommunication industry in Sri Lanka is having very fast growing and expanding services to their customers. Also, the increasing number of telecom service providers has entered to the industry during past decades, with much competitive Tariffs. At the same time, a regulatory body called "Telecommunications Regulatory Commission of Sri Lanka" (TRCSL) was legally formed under the Sri Lanka Telecommunication (Amendment) Act No. 27 of 1996 and start benefiting to the nation in terms of quality, choice and value for money by extending the optimum conditions of the telecommunications industry in Sri Lanka. The main challenge of the service provider is to sustain with the competitive Tariff reductions and advancement of their services to customer door step demanding by the industry. Not like in other industry, the telecom customer is having the freedom to select any service provider by own decision without facing any monopoly or other influence by the industry. This automatically creates the industry to reduce their OPEX & CAPEX continually. The CAPEX is always increasing and the reduction possibility exists only with OPEX in the telecom industry. Electricity is contributes to the major portion of OPEX of remote telecom site operations. The electricity by means of Diesel Generator (DG) operation or Commercial supply (CEB/ LECO) is always a difficult facility in remotely operated telecommunication base stations. This is due to the nature of the location of the selected site and the quality of the nearest/ rural commercial supply. Due to this, the site needs to run with the DG in most of the time period of the day or face with service outages due to interruptions of the electricity with huge OPEX and unexpected losses in income. The main objective of this research project is to develop a system for automatic voltage regulation at remote telecommunication sites with customized features. The unit is expected to operate under extreme climate, ii environmental & power abnormality conditions to regulate & maintain reliable & accurate sinusoidal voltage profile to the sensitive telecommunication equipments. In addition, the development of the unit should capable to meet the protection requirements from various environmental & power abnormalities, modular construction for easy customization at initial site installations & maintenance, Increased system efficiency, output power quality, fast voltage correction, long life of operation, noise free regulation, less maintenance attention, automatic monitoring, controlling & operation, relatively small construction with lightweight package at lowest possible cost will also be some of the expected outcomes of this development. This research paper will present the background review, detail technical analysis, theoretical development & design, financial analysis and possible areas of further improvements. At the same time, sample implementation also carried out in several sites of Lanka Bell Ltd was proved a considerable financial benefit back to the company. The outcomes of this research will be a remarkable development in the telecom industry. We also supposed to share this knowledge with all the interesting parties to extend the benefits not only to the telecom service providers, but also to the customers by means of lowest tariffs. CONTENT Declaration * i Abstract ii Acknowledgement vii List of Figures viii List of Tables ix 1. Introduction 1 1.1 Objectives of the development 1 1.2 Proposed Features 1 1.3 Why the power quality is important 2 1.3.1 Voltage sags 3 1.3.2 Brownouts ...... 3 1.3.3 Over voltage & Surges 3 1.3.4 High voltage spikes 4 1.3.5 Electrical noise 4 1.3.6 Blackouts & Mains failure 4 1.3.7 Summary of the Solutions 5 1.4 Research Area 6 1.5 Expected Outcomes . 6 2. Background review & Motivation 8 2.1 Power to the telecom sites 8 2.2 Standard Equipments in BTS 8 2.3 Standby Diesel Generator operation due to low voltage 9 2.4 Dedicated Transformers for distance sites 10 2.5 General applications of Voltage stabilizing systems 11 2.6 Effects of supply voltage variations in equipment operation 11 3. Results of Sample survey 14 3.1 Introduction on the sample site & test equipments 14 3.2 Sample Graphs of Voltage & Current distortions 15 3.3 Suggestions for Voltage correction 18 4. Development Areas & Techniques 4.1 Proposed Developments 20 20 iv 4.2 Proposed 30 Features - Summery of the Techniques 22 5. Theoretical Development 26 5.1 Development Areas 26 5.2 Problem Identification and Categorization 27 5.3 Analyze the problem, Solutions & related issues 28 5.4 Technical approach for the proposed solutions 33 5.4.1 Define the RBS Models ....... 33 5.4.2 Identify the Design Requirements for each Model 35 5.4.3 Theoretical methodology of the design 37 5.4.4 Various design techniques used in voltage stabilizers 37 5.4.4.1 Electronic Servo / Electro - Mechanical Design 37 5.4.4.2 Solid State Saturable Reactor Design 39 5.4.4.3 Magnetic Induction Solid State Design 40 5.4.4.4 Ferro-Resonant Super Isolation Solid State Design 41 5.4.4.5 Electronic Tap Changing Solid State Design 42 5.5 Design of the Servo Motor system 43 5.5.1 Aim of the design 43 5.5.2 General Design Procedure 43 5.5.3 Constructional & Operational characteristics 44 5.5.4 Specifications & Design parameters 46 5.5.5 Selection of Materials 46 5.6 Design of Autotransformer in the stabilizer 47 5.7 Design of control system in the stabilizer 49 5.8 Achieving the highest accuracy of the output Voltage 52 5.9 Incorporate protections for the system 55 5.9.1 Short-circuit and overload protection 55 5.9.2 Over and Under Voltage protection 55 5.9.3 Safe Start, Bypass and Circuit Breaker protection 55 5.9.4 Lightning & Surge Protection 56 5.9.5 Auto/Manual Control & Emergency by-pass 56 5.9.6 Line / Output Reactor 56 5.9.7 RFI / EMI Filters 57 5.9.8 Sine Wave Motor Protection Filters 57 5.10 Maintenance & Monitoring facilities 58 5.11 Energy Efficiency, loss reduction & power savings 59 5.11.1 Energy-Efficiency in Motors 60 5.11.2 Determine Cost Effectiveness of the Motors 61 5.11.3 Energy optimization of equipments in operation 62 • 5.12 Technical Analysis on the Power Quality of LV network 64 5.12.1 Introduction on Power Quality 64 5.12.2 Mathematical modeling of Load level voltage fluctuation 64 5.12.3 Power Quality disturbances 67 5.12.4 Voltage fluctuations . 68 5.12.5 Managing PQ Problems 72 5.12.6 Power Quality Standards 73 6 Results and Analysis 75 6.1 Overview of Outcomes 75 6.1.1 Direct Financial Benefits 75 6.1.2 Operational Overhead Reductions 76 6.1.3 Technical Benefits 76 6.2 Reduction of the Network Outage Time . 77 6.3 Reduction of the Customer Complains 79 6.4 Reduction of the Operational Overhead 81 7 Financial Feasibility Analysis 84 7.1 Overview ..... 84 7.2 Cost Calculation for Generator Operation 85 7.2.1 Generator as Back up Power Source 85 7.2.2 Generator as Main Power Source 87 7.2.3 Summary of DG cost vs. running hours 89 7.3 Analysis of Traffic on standard RBS site 89 7.4 Analysis of Tariff applicable for customers . 90 7.4.1 Tariff Charges on post paid customers 91 7.4.2 Tariff Charges on Pre paid customers 91 7.4.3 Tariff Charges on IDD customers 92 7.4.4 Summary of Revenue on call charges for 24hrs 92 7.5 Revenue saving per day on each RBS Model 93 8 Conclusion 96 References 97 Appendix . . . 99 vi ACKNOWLEDGEMENT I would like to thanks my supervisor, Dr J.P. Karunadasa, Head of Electrical Engineering department, for his right direction, great insights, perspectives, guidance and sense of humor. My sincere thanks go to the former Head of Electrical Engineering department Professor H.Y.R. Perera, course coordinator, Dr. Lanka Udawatta and all the academic staff who helped in various ways to clarify the things related to my academic works in time with excellent cooperation and guidance. Sincere gratitude is also extended to the people who serve in the Department of Electrical Engineering. I also thanks to Mr. Krishan Gamage, General Manager, Technical Operations, Lanka Bell Limited for arranging the required funding for the research implementations, Mr. Kusal Saranath, Divisional Manager, Technical Operations, who gave special guidance on clarifying technical matters and, Anura Liyanage (Engineer, Maintenance) for his time on helping me to conduct the preliminary technical surveys and gathering technical literatures in many of the sites in various places in Sri Lanka. I also like to thank my wife, Inoka for her time & kind effort to re-check the draft copy of the Thesis to make this a perfect presentation. Lastly, I should thanks many individuals & friends who have not been mentioned here personally in making this educational process a success. May be I could not have made it without your supports. S.S.K. Thotagamuwage vii LIST OF FIGURES Fig 2.1: Equipment block diagram of standard RBS room. Fig 3.1: Test arrangement of Equipment at Kuruwita Lanka Bell RBS site Fig 3.2: Proposed rearrangement of equipments inside the Kuruwita Lanka Bell site Fig 5.1: Proposed arrangement of equipments inside the RBS site Fig 5.2: Schematic arrangement of Model 1. Fig 5.3: Schematic arrangement of Model 2(a). Fig 5.4: Schematic arrangement of Model 2(b). Fig 5.5: Schematic arrangement of Model 3. Fig 5.6: Circuit arrangement of Electronic Servo / Electro - Mechanical Design Fig 5.7: Circuit arrangement of Solid State Saturable Reactor Design Fig 5.8: Circuit arrangement of Magnetic Induction Solid State Design Fig 5.9: Circuit arrangement of Ferro-Resonant - Super Isolation Solid State Design Fig 5.10: Circuit arrangement of Electronic Tap Changing Solid State Design Fig 5.11: Schematic diagram of Servo motor system Fig 5.12: Standard assemblies of Servo motor Fig 5.13: Block diagram of a servo system controls Fig 5.14: Standard control circuit of Automatic voltage stabilizer Fig 5.15: The growing gap of the Peak oil discovery and the world consumption Fig 5.16: Simple model of power system Fig 5.17: Phase diagram of supply voltage Fig 5.18: Characteristics of voltage fluctuations Fig 6.1: Graphical representation of network outages in last 4 months Fig 6.2: Graphical representation of Customer Complain in last 4 months Fig 6.3: Graphical representation of main actual OPEX in last 4 months Fig 7.1: Traffic curve (in Erlang) of Badalkumbura RBS site for one week period Fig 7.2: Traffic curve (in Erlang) of Hatharaliyadda RBS site for one week period VIII LIST OF TABLES Table 1.1: Performance of some the main present power solutions Table 2.1: Generator Diesel & Potter Cost at Under Voltage sites Table 2.2: Cost of Transformer installation at CEB unavailable sites (Lanka Bell Ltd) Table 2.3: Effect of voltage variations on equipment operations Table 3.1: Technical specifications of the AVS tested at the Kuruwita Lanka Bell site. Table 4.1: Summery of the Proposed 30 with techniques & outcomes. Table 5.1: Categorization of RBS sites considering power & voltage constrains Table 5.2: Details of RBS sites having highest Gen running & possibility of the solutions Table 5.3: Categorization of RBS sites to 4 models considering existing site conditions Table 5.4: Environmental requirements of the standard RBS equipments Table 5.5: Design requirements of the RBS Models in detail Table 5.6: Advantages & Disadvantages of Electronic Servo / Electro - Mec. Design Table 5.7: Advantages & Disadvantages of Solid State Saturable Reactor Design Table 5.8: Advantages & Disadvantages of Magnetic Induction Solid State Design Table 5.9: Advantages & Disadvantages of Ferro-Resonant - Super Isolation Design Table 5.10: Advantages & Disadvantages of Elec. Tap Changing Solid State Design Table 5.11: Energy efficient equipment replacements for telecom sites Table 5.12: Short Duration Voltage Variation categories Table 5.13: Maximum harmonic current distortion as per the IEEE 519 Table 5.14: Supply voltage measurement as per European Standard, EN 50160 Table 6.1: Main categories & Information Sources of Direct Financial Benefits Table 6.2: Main categories & Information Sources of OPEX Reductions Table 6.3: Main categories & Information Sources of Technical Benefits Table 6.4: Summary of network outages in last 4 months Table 6.5: Summary of Customer Complains in last 4 months Table 6.6: Summary of the budgeted OPEX categories for maintenance ix Table 6.7: Summary of the actual OPEX in last 4 months Table 7.1: Generator operation cost vs. running hours at radio base station site. Table 7.2: Tariff Charges on post paid customers. Table 7.3: Tariff Charges on pre paid customers. Table 7.4: Tariff Charges on IDD customers. Table 7.5: Revenue calculation on call charges for a period of 24 hours Table 7.6: Revenue saving per day calculation on each RBS Model Table 7.7. Details of RBS sites having highest Gen running & possibility of the solutions Table 7.8: Total saving per day calculation on each RBS Model Chapter 1 INTRODUCTION 1.1 Objectives of the Development The main objective of this research project is to develop a system for automatic voltage regulation at remote telecom sites and incorporate many of the advanced features & facilities for customized use. It is supposed to be used in remote telecom sites, having day-to-day power quality & continuity problems that frequently interrupt the operation of the critical equipments & services. It is mainly focused on reducing the Diesel Generator operation and frequent customer service outages in the most critical remote sites (backbones of the network), at the 1st stage of implementation. The final objective of the research is to propose a methodology to reduce the OPEX in telecom operation by advancing the voltage regulating systems available in the market, to best-fit with the telecom requirements. 1.2 Proposed Features The unit is expected to operate under extreme climatic, environmental & power abnormality conditions to regulate & maintain reliable & accurate sinusoidal voltage profile to the sensitive electronic & telecommunication equipments. In addition, the development of the unit should be capable to meet the protection requirements specified by the equipments installed from environmental & power abnormalities under variety of site conditions. The modular construction for easy customization at initial site installations & easy maintenance at regular intervals is also expected. Increased system efficiency, output power quality, fast voltage correction, long life of operation, noise free regulation, less maintenance attention, automatic monitoring, controlling & operation, relatively small construction with lightweight package at lowest possible cost, are some of the expected outcomes of this development. 1 1.3 Why the Power Quality is important? For electrical systems to function properly, it is necessary to make sure that' the quality of the power feeding them is of a sufficient quality to ensure that performance is not impaired or system life expectancy reduced. Without the proper power, an electrical device or load may malfunction, fail prematurely or not operate at all. There are many ways in which electric power can be of poor quality and many more causes of such poor quality. Power supply problems are caused by various sources, for example distribution network faults, system switching, weather and environmental conditions, heavy plant and equipment, or simply faulty hardware. The most common solution for those power quality problems in industry is to have online UPS (Uninterruptible Power Supply) and will often be viewed as the obvious choice [1]. But, these are usually expensive to buy and have high ongoing maintenance and support costs. In many less developed countries the high technology skill sets required to maintain such systems are not readily and inexpensively available. For most applications where the loss of mains is not really a critical issue, or can be accommodated by the use of a standby generator, the deployment of an Automatic Voltage Stabilizer / Regulator or AC Power Conditioner will be a far more cost efficient solution both in terms of initial outlay, ongoing maintenance, support costs and the required local- skill sets required to install, maintain and support the solution [2], In other word, over engineering a solution due to a lack of understanding on the power quality issues being experienced is an all too common mistake that can deeply impact. Regardless of the cause of the problem, the resulting power quality issue will include one, or more, of the power problems as follows [1], Any system to work under those conditions should be capable to withstand and sustain to operate smoothly. 2 1.3.1 Voltage Sags Voltage Sags are short duration decreases in the mains supply voltage which generally last for several cycles. The formal definition is the voltage below 80 to 85% of rated RMS voltage for 2 or more cycles. The typical symptoms are locking of Sensitive equipment or data loss and system resets. Common Causes of the sags are Heavy equipment turned on, starting large electrical motors, switching of the mains supply. Commonly available Solutions are AC Voltage Stabilizer, AC Power Conditioner & Uninterruptible Power Supply. 1.3.2 Brownouts Brownouts are long term sags in the mains supply voltage which can last up to several days. The formal definition is a steady state of RMS voltage under nominal by a relatively constant percentage. The typical symptom is reset of Equipment or even shutdown. Common Causes of the brownouts are Heavy equipment turned on, starting large electrical motors, switching of the mains supply or just low voltage output from the generating source. Commonly available Solutions are AC Voltage Stabilizer, AC Power Conditioner & Uninterruptible Power Supply. 1.3.3 Over-Voltage & Surges Over-Voltage & Surges are short duration increases in the mains supply voltage which generally last several cycles. The formal definition is voltage above 110% of the rated voltage for 1 or more cycles. The typical symptoms are premature failure & other effects when surges. The high voltage causes wear and tear and general component degradation. This is often unnoticeable until failure occurs. Unusual heat output can be an early sign of problems ahead. Common Causes of this is Heavy equipment being turned off. 3 Commonly available Solutions are AC Voltage Stabilizer, AC Power Conditioner & Uninterruptible Power Supply. 1.3.4 High Voltage Spikes High Voltage Spikes are very fast high energy surges or spikes in voltage lasting only a few milliseconds. The formal definition is Rapid Voltage peak up to 6,000 volts with duration of 100msec to Vz a cycle. The typical symptoms are lock or hang, crash and even suffer damage of equipment which inevitably causes data loss and corruption. Common Causes of these spikes are switching of equipment, especially heavy inductive loads, arcing faults or atmospheric electrical disturbance, such as lightning strikes and static discharges. Commonly available Solutions are AC Voltage Stabilizer, AC Power Conditioner, Isolation Transformer, and Uninterruptible Power Supply. 1.3.5 Electrical Noise Electrical Noise is a high frequency noise either common or normal mode. The formal definition is Electrical noise is high frequency interference on the incoming mains supply. The typical symptoms are Processing errors, computer lock-up, burned circuit boards, degradation of electrical insulation and equipment damage. Common Causes of this noise are Electric motors, relays, motor control devices, broadcast transmission and microwave radiation. Commonly available Solutions are Isolation Transformer, AC Power Conditioner & Online uninterruptible Power Supply. 1.3.6 Blackouts & Mains Failure Blackout and Mains Failures occurs when the mains supply fails completely this is known as a total mains failure or blackout. The formal definition is Loss of incoming mains supply. 4 The typical symptoms are complete disruption of equipment operation. A break in the mains supply of only several milliseconds is sufficient enough to crash, lock or reset many of the components that make up a typical data or voice processing IP network, such as PC, terminal, console, server, PBX, printer, modem, hub or router, if no other back up source is provided. Common Causes are Storms, lightning, wind and utility equipment failure. Typically occurs as a result of loss of power, a mechanical failure, or overloading by consumers. Commonly available Solutions are Uninterruptible Power Supply & Diesel Generator. 1.3.7 Summary of the Solutions Various solutions are available, which provide varying degrees of protection at different prices in the market. They react to changes in the main power supply and are suitable for specific power problems, with varying reaction times and approaches [1 ]. The performance of some of the solutions under variety of power conditions can be tabulated as follows. Power Problem Power Conditioners Automatic Voltage Stabilizers Filters and Filter Strips TVSS UPS Sags/ Brownouts Some yes - - Yes Surges Some • Yes - - Limited Spikes/ Transients Yes Limited Yes yes Yes Electrical Noise Yes Limited Limited - Yes Harmonics - - - - Yes Frequency variations - - - - Yes Table 1.1: Performance of some the main present power solutions 5 1.4 Research Area Under this part of the project, the main concentration is to identify the specific requirements & modifications which needs to incorporated with the basic voltage regulating unit, in order to operate under the telecommunication environments with extremely abnormal site conditions. Selected basic unit will be tested under various site conditions to identify the development requirements and the test results will be analyzed in detail to answer the current issues of the sites which need to be addressed in the first stage. The identified requirements will be implemented to develop a model to suite the tested environment. The final results will be used to present the Technical Feasibility of the project. At the end of this report, the preliminary theoretical development will be discussed and the proposed equipment arrangement along with the electrical installation modifications will also be identified. The direct & indirect financial benefits will be identified and the existing operation overhead is suppose to be reduced in greater extend and this will be used to prove the financial feasibility of this project in order to extend the next part of the research development. 1.5 Expected Outcomes The research development will give the following outcomes in terms of direct financial benefits, operational overhead reductions & much more technical easiness. Direct Financial Benefits • Recover the profit/ revenue from network up time • Customer satisfaction & retention due to unbreakable service • Reduction of expenses for failure recovery due to power problems • Minimum part replacements by reducing the equipment failures • Other financial benefits related to network revenue 6 Operational Overhead Reductions • Minimum use of Diesel Generator for the operation • Minimum attention & visits for day-to-day failure recoveries • Low routine maintenance visits with reduction of maintenance cost Technical Benefits • Improve the efficiency of power to equipments, hence low electricity cost • Extending the equipment operational lifetime with quality power & reduced interruptions • Maintain the room temperature in the recommended range for healthy operation as specified by the telecom equipment manufacturers • Reduce the losses in the equipment operation with high quality power • Reduced environmental & power surges in to the room and improved protection for the systems • Etc... 7 Chapter 2 BACKGROUND REVIEW & MOTIVATION 2.1 Power to the Telecom sites Low Voltage & bod power quality are common problems in most of the Telecommunication Radio Base Stations (RBSs) in Sri Lanka; mainly due to the specific locations of the selected telecom sites to suite the transmission requirements [3], The best site in terms of transmission can be located at top of mountain or at the middle of a jungle where the coverage & transmission capacity is optimum. However, most of the times, nearest commercial power line are more than 1 ~ 3 Kms away to the mentioned site. Hence the line drawn up to the site will not maintain the standard voltage window, required specially for most of the M&E equipments and the ultimate result is the equipments have to be fed by low voltage supply or request for new Transformer. 2.2 Standard Equipments in BTS The basic equipment arrangement of a telecom Base Station is as follows. Fig 2.1: Equipment block diagram of standard RBS room. 8 The line voltage drop is first sensed by the Automatic Transfer Switch (ATS) of the Generator connected and once the voltage goes below than the pre-set limit (most of the time, 185Vac); the Generator will automatically get connected to the system. Note: The single line diagram of ATS panel and equipment power panels can be drawn as per the IEC standard [18] and are annexed at the end. 2.3 Standby Diesel Generator operation due to low voltage As the voltage profile of the incoming line always drops, the Generator will operate continually and the operation cost in terms of Diesel, portal charges, frequent maintenance & technical attention will be higher. The total cost will exceed around 2 - 3 times that of the normal electricity cost (around Rs. 30,000 per month) and this will indirectly affect the operations cost budget and additions of the same of all the same sites will be a significant figure which will not recommended to extend through out the life of the infrastructure [4]. Some of the previous statistics of Generator diesel cost (month of April 2008) at under voltage sites (owned by Lanka Bell Limited) can be tabulated in descending order as follows. It is observed that the operational cost at sites with significant voltage drops in comparatively high compared to the cost at site where the generator operate only for short period of time. RBS Site Name Cost Rikillagaskada 90,304 Mundalama 89,840 Mapalagama 88,200 Police Park 87,520 Nildandahena 86,904 Ulapane 85,998 Pallebaddara 84,300 Ingiriya 82,500 Dompe 78,480 Yatiwawala 78,474 Galenbindunuwewa 74,370 Bellwood 73,074 Madamahanuwara 72,180 Pogoda 72,000 Gatabaruwa 70,640 RBS Site Name Cost Ginigathhena 62,556 Minneriya 58,240 Kiriella 55,060 Maha Oya 53,196 Culan 52,360 Robare 51,584 Aralaganwila 48,240 Bogawanthalawa 48,120 Kohan 45,815 Girandurukotte 44,220 Dabulla 40,902 Morawaka 40,080 Balangoda 39,195 Galagedara 38,496 Baragala 36,270 RBS Site Name Cost Wellawaya 24,986 Higula 24,525 Attugala 24,030 Adalachchena 23,616 Badulkubura 23,374 Hettimulla 22,923 Pothuwil 22,568 Middeniya 22,075 Eipitiya 21,250 Agbopura 20,880 Rilagala ' 16,060 Sooriyawawa 15,257 Naugala 14,819 Ambuluwawa 14,436 Narammala 13,617 9 Ankubura 69,368 Deniyaya 67,360 Ibbagamuwa 67,284 Karandeniya 66,550 Kaudupalalla 64,962 Hatharaliyadda 64,962 Endana 64,080 Bopitiya 64,000 Nittabuwa 64,000 Kuruwita 63,920 Puliyamkulam 33,760 Karagahathanna 33,684 Parakaduwa 33,642 Madagama 33,046 Allawwa 32,841 Hanwella 32,250 Diyabeduma 32,160 Jayanthipura 32,160 Pitigala 29,650 Awissawella 25,680 Belunmahara 13,360 Nwalapitiya 13,280 Gandara 13,233 Warakapola 13,201 Nikawaratiya 12,816 Hanguranketa 12,030 Kalawana 11,823 Palawaththa 11,452 Waduraba 11,228 Lunuwila 10,160 (network data of Lanka Table 2.1: Generator Diesel & Potter Cost at Under Voltage sites Bell Ltd in April 2008) 2.4 Dedicated Transformers for distance sites In addition to the above DG cost, some of the sites located faraway to commercial line can not get power in the normal way (as CEB not accepted to provide from the existing lines) and needed to install separate Transformers with huge cost. As the transmission opportunity is much more important, industry will continue with those sites also with huge cost for electricity infrastructure. Some of the same sites with electricity infrastructure cost are listed bellow. ROUGH DISTANCE FROM CEB OH LINE (Km) DISTANCE ENGINEERS CEB 70KVA TOTAL COST (Rs.) RBS FROM ESTIMATION ESTIMATION TRANDPORMER NEAREST F S R L T (Rs.) HT (Rs.) COST (Rs) HOUSE (m) Het t imulk 500 2.1 600,000.00 4,410,000.00 1,300,000.00 6,310,000.00 Madamahanuwara 200 1.3 40,000.00 2,815,000.00 1,300,000 00 4,155,000.00 Mapalagama 1000 1.4 100,000.00 2,980,000.00 1,300,000.00 4,380,000.00 Ukpane 200 1.0 670,000.00 2,102,200.00 1,300,000.00 4,072,200.00 Gakgedara 100 2.8 600,000.00 5,937,750.00 1,300,000.00 7,837,750.00 Ankubura 2000 1.0 750,000.00 2,180,900.00 1,300,000.00 4,230,900.00 Katugastota 400 0.5 650,000.00 1,080,920.00 1,300,000.00 3,030,920.00 Hataraliyadda 50 1.1 775,000.00 2,220,850.00 1,300,000.00 4,295,850.00 Kawdupelelk 50 3.2 500,000.00 6,655,000 00 1,300,000.00 8,455,000.00 Niwithigak 100 2.4 5,100,000.00 5,100,000.00 1,300,000.00 11,500,000.00 Ridipana 900 4.8 775,000.00 10,000,000.00 1,300,000.00 12,075,000.00 Nildattdahiriita 500 2.1 700,000.00 4,418,250.00 1,300,000.00 6,418,250.00 Rikilkg^skada 1000 2.0 775,000.00 4,200,000.00 1,300,000.00 6,275,000.00 Morawaka 1200 3.6 775,000.00 7,560,000.00 1,300,000.00 9,635,000.00 Table 2.2: Cost of Transformer installation at CEB unavailable sites (Lanka Bell Ltd) 10 All the above sites, power can be taken just near to the site with new Transformers purchased by the telecom operator (by Lanka Bell Ltd or shared with other operators in the same site) and voltage problems will not happen. But the cost of the electricity infrastructure is very high & payback period of the investment is beyond the expected. However, all the other sites which can extend the power line up to the site (accepted by the CEB) have to face with voltage problems and need separate system for voltage regulation [19], [20], [21], [22]. 2.5 General applications of Voltage stabilizing systems In the market, Voltage stabilizing systems can be found for variety of applications. They are suitable for supplying resistive, inductive, and capacitive loads. Automatic Voltage Stabilizers are used at home and abroad, in part under extreme climatic conditions. They stabilize the power supply for • Computers, X ray, Laboratories and test facilities • Industrial electric heaters, Control centers for heating systems, e.g. in hospitals • Data processing systems, Telecommunication & radio transmission and receiving systems • Magnetic equipments and Transformers • Air conditioning equipment, Illumination systems, etc • Machine tools, motors and Welding equipment 2.6 Effects of supply voltage variations in equipment operation Automatic Voltage Stabilizers operate on a closed loop control. The output voltage is measured and compared with a highly stable reference voltage in an electronic control unit. Whenever the output voltage deviates from the reference, the servomotor is switched on until the output voltage has again reached its nominal value. This results in a booster voltage, corresponding to the deviation, to 11 be added to or taken away from the line voltage. The correction of the voltage is highly recommended for sensitive equipment operations and more efficient for all other equipments. Some of the effects under voltage variation conditions can be tabulated as follow [2]. Load Voltage Reductions Effects Voltage Increases Effects Computers An 8% drop will often cause computer errors and downtime. A 10% rise will cause computer damage, errors and downtime. Lighting A 10% voltage drop reduces lumen output by over 25% (15% for florescent tubes). Infra Red lamp heat output is reduced by over 20.% A 10% volt rise reduces life expectancy of incandescent lamps by over 50%. Radio & TV Transmission Volt drop will reduce quality of the transmission and coverage range. Over voltage by 2% will significantly reduce tube life. Photographic Processing A 5% volt drop will increase exposure times by 30% and reduce quality of color printing significantly. Voltage rise during printing cycles will cause inferior results X-Ray Equipment A 1 % change in the filament voltage of an X Ray tube will produce an 8% change in the anode current. When used at its maximum rating an X Ray tube will be permanently damaged in the case of a 5% volt rise. Magnetic Eguipment A 10% volt drop can cause relays / contactors to open chatter. Solenoids become sluggish and vibration will cause malfunctions and overheating. Over voltage will cause magnetic core saturation high current and overheating. Wear and distortion is increased. Welding Equipment A 10% volt drop will increase a welding cycle by 20% if weld guality is to be maintained. A 10% volt rise will overheat a weld, reducing quality and causing possible "burn through". 12 Transformers At 100 kVA a 10% drop will reduce transformer rating to 90%. A 10% rise will considerably increase core losses and decrease efficiency proportionally. AC Motors A 10% volt drop reduces torque by approximately 18%. Motor life expectancy is reduced due to overheating. A 10% volt rise causes higher starting current and reduces power factor by approximately 5%. Table 2.3: Effect of voltage variations on equipment operations The Voltage regulating units available in the market can handle general situations but when the site conditions become complicated, the unit will not support for majority of the operating requirements. With the requirements identified above, expectation of this research is to develop best suitable unit for voltage regulations with most of the added features [20], [21], [22], 13 Chapter 3 RESULTS OF SAMPLE SURVEY 3.1 Introduction on the sample site & test equipments In the above test, Automatic Voltage Stabilizer (AVS) of Servo Motor Type (in- house assembled unit with market available components) installed to one of the inductive load (Air Conditioning unit) at the input point inside RBS and power conditions monitored at various places on the system to identify the variations of the voltage & other parameter under low voltage environment. The main objective was to understand the operation of AVS and the development requirements which not supported by the AVS unit used. The environment parameters of the selected sample site are as follows. Sample Site: Lanka Bell Limited, Kuruwita Base Station. Test period: 13th July 2008, from 10.30am to 12.30pm Weather Condition: Light rainfall Power supply: CEB 30 Amp 1 phase (voltage varied, 100 ~ 250Vac 1 ph) Test equipments used at the above test are as follows. 1 FLUKE 43B Single phase - Power Quality Analyzer 2 KYORITSU AC/DC Clamp Meter 3 Single phase 3KVA, 140 ~ 250Vac, Servo Motor, Automatic Voltage Stabilizer M&E equipments installed in the RBS can be listed as bellow. i. HUWEVI BTS 3606 Rack (1 No) ii. Emerson PS48300 -1 A/30-x2 Rectifier rack (1 No) iii. Air Cooled, Wall mounted, Split A/C, 12,500 Btu/Hr - Mitsubishi (2 No) iv. F.G.WILSON 12.5KVA Generator (1 No) 14 v. Bulk Head -Whether Proof Security Light with 7W Compact Fluorescent Lamp (1 No) vi. 4ft-l x 36W, Surface Mounted Fluorescent Lighting Fixture (2 No) vii. 2ft-lx8W, Surface Mounted Fluorescent Emergency Fixture (1 No) viii. 230V,AC, 9" Dia Exhaust Fan with Auto Shutter (1 No) 3.2 Sample Graphs of Voltage & Current distortions Test graphs obtained from the power quality analyzer at following test points of the power system and the variations of the test parameters can be clearly identified. Commercial Main power 1 ph 30A CEB Base Station Equipments PDF G2 61 G4 CEB ATS (manul position) G5 1 ph 12.5kva Generator 1ph AVS 3kva 1ph -/ t- 1ph G3 3ph -| 1 A/C unit 1 I Alarm panel 1ph 1ph -I I A/C unit 2 I Exaust fan j I Light & Other Rectifier Rack Fig 3. J: Test arrangement of Equipment at Kuruwita Lanka Bell RBS site The low voltage is a common problem to the distanced/ rurally connected customers and the quality of the power delivered is not suitable to operate sensitive equipments [16], Graphs obtained at points G1 to G5 and the load arrangements are also mentioned below. 15 UOLTS/AMPS/HERTZ HOLD <6 253,6 U= MAX 2272 Us AUG 1S7J5 U= MIH G13 Jun 2008 10:44:49 13 Jun 2008 10:36:54 13 Juri 2008 10:40:10 180U 116? A" 3)07 As 0.01 A= MAX AUG MIH 13 Jun 2008 10:39:31 13 Jun 2008 10:36:48 15JM In 5m 0.00A Graph 1 (G1): Stabilizer output (Voltage, Current & Frequency) to the AC unit 1 UOLTS/AMPS/HERTZ HOLD < t l iTMMil m n . i „ n snna « 1955U= MAX 13 Jun 2008 10:57:25 17416 Us AUG 1397U= MIH 13 Jun 2008 10:57:41 200U — — 140U 585 As MAX 13 Jun 2008 11:02:31 300 As AUG 0,01 As MIH 13 Jun 2008 10:54:52 L • " : • 6.0Pfl 5m ™ 0 f l I n Graph 2 (G2): Normal CEB input (Voltage, Current & Frequency) to the AC unit 1 UOLTS/AMPS/HERTZ HOLD < t UOLTS/AMPS/HERTZ HOLD <£ nWiHi l i i rn •>manna ii-m-M 205i8Us MAX 13 Jun 2008 11:13:07 1759 Us AUG 1267 Us MIH 13 Jun 2008 11:18:51 l iUf l l i l ' l £> 13 Jun 2008 11:29:10 2136Us MAX 13 Jun 2008 11:24:44 1948 Us AUG 1556Us MIH 13 Jun 2008 11:25:52 *>nm i i • - . * • k. a! Sn - 1 , .T . . 220U i4ou • " ' • ' " ' 'A*- v ' kr. 160U 128 As MAX 13 Jun 2008 11:13:02 1 046 As AUG 0.01 As MIH 13 Jun 2008 11:12:02 | 1339 As MAX 13 Jun 2008 11:25:52 566 As AUG OjOIAs MIH 13 Jun 2008 11:22:59 150A 15J0A U T ^ '5m 1m ' 5m 0 J , 0 A Graph 3 (G3): Normal CEB input (Voltage, Current & Frequency) to the Rectifier Rack (profile with start up characteristics of the Rectifier unit) 16 (JOLTS / AMPS / HERTZ HOLD < t B M 1823 Us MAX 142jOUs AUG 10Q8 Us MIH 180U Aj,1 1370 A" MAX 654 As AUG 473 A= MIH - ^ p x Q13Jun 2008 11:45:45 13 Jun 2008 11:44:34 13 Jun 2008 11:39:20 13 Jun 2008 11:45:03 13 Jun 2008 11:45:03 ilJtjOAl U0LTS/AMPS/HERTZ HOLD ! i l>l G13 Jun 2008 12:03:14 49 THD MAX 13 Jun 2008 12:02:08 41 THD AUG 3PTHD MIH 13 Jun 2008 11:59:25 15.0THD OJOTHD 30s 120s Graph 5 (G5): Normal CEB power input (Sags & Swells and THD) to the cabin with all loads UOLTS/AMPS/HERTZ HOLD 90% Ambient Temperature minus 10" - 40° Q Relative Humidity <90% Temperature Rise 2MC Manufacturing Standard ISO 9001 Weight 5.3 legs lOkgs 12 kgs Dimensions 2tO (W) x 165 (H) x !95(D)mnt 240(W) x 200(H) x Z80(0)tran Z«KW}x 230(H) x300(D)mm Table 3.1: Technical specifications of the AVS tested at the Kuruwita Lanka Bell site. The identified gap is supposed to be filled with the development under this project and detailed design & implementation schedule will be discussed in the Chapter 5, under the Theoretical Development. 9 2 9 " ! 19 Chapter 4 DEVELOPMENT AREAS & TECHNIQUES 4.1 Proposed Developments Followings are the proposed features/ development areas with techniques which will incorporate to the Automatic Voltage Stabilizer (AVS) unit specially developed for the telecommunication applications [20], [21], [22], 1. Expanded input voltage window by higher rated windings or power circuits and phase selector to select best available phase. 2. Maintain non distorted sine wave output under distorted input conditions with static line conditioner, Isolation Transformer and RFI/EMI/EMC/EFT filter blocks. 3. Fast respond for voltage correction by small stepped servo transformer a. Select servo motor with small steps that can handle lowest min/volt. b. Higher voltage correction time by increasing the speed and performance of the synchronous servo motor. 4. Main Controller panel for the overall management of the M&E equipment operations inside the cabin and equipped with Generator selection, Thermal management. Alarm management & logging, Air Conditioner / fan Control, AC distribution customization, power line protection, etc. 5. Protections from power surge, lightning, over current, phase failure, etc by incorporating separate protection systems as per the site conditions a. MOVs are added on across the input of the supply line to protect from transient voltage surge or spikes. b. Lighting and Surge protection by built in Class-B & C diverters. c. Short circuit protection on output side by selecting fuses and the overload protection by thermally or electronically acting trip switches. 20 d. Coils are wound with paper covered electrolytic grade copper strip or synthetic enameled copper conductors to provide & ensure high short circuit strength. e. Possess protection & quick isolation of incoming supply under overloading or short circuit conditions by high quality MCB. 6. Higher efficiency of operation by reduced heating, warn out and losses a. Reduce the losses of electrical motors which lead to damage of cables, switches, relays, contactors and other associated equipments by regulating the voltage in acceptable range. b. Achieve higher reliability & trouble free performance by employing self lubricating carbon roller assemblies instead of ordinary carbon brushes. c. Minimize copper losses & iron losses by wound with heavy section of multi strips electrolytic copper and special lamination. 7. Status monitoring capability with alarm extending for remote monitoring a. Install analog voltmeters, ammeters, phase indicator lamps, etc as basic indicators on the unit for monitoring the unit status. b. Provide advanced indicating options to monitor status of working, excitation, sensing voltage, and even the exact failures of the system itself by extending the alarms to network management center and/ or shown on the unit itself. c. Site Status Communication by SMS / GPRS based and RS232 interface support for integration with the remote system and could even be works with CDMA phone. d. Additional relay contacts to be operated in a secure manner (guarded by calling party identification) to provide remote control operation at site. 8. Startup delay protection for inductive loads under transient conditions a. Include start up delay to preventing any damage to inductive load equipments such as Air conditioners under transient condition and auto restart on main return to within pre-programmed set-point. 21 9. Rough construction for outstotion applications to prevents moisture and contaminants in harsh environments. a. Construction with electrically & mechanically reliable components such as variable transformers with motor drive, electronic control units. b. The core of voltage controller is constructed from cold rolled, grain oriented, low loss, annealed laminations of electrical sheet steel to make the structure rigid and robust to reduce magnetic noise. 10. Module/ Detachable construction for easy customization to suite the variety of installation, transportation & replacement conditions. 11. Less maintenance attention by component design for extended & un-man operation conditions at remote sites. 12. Incorporate with connected equipments to select the best optimum operation patterns in order to reduce the operation cost while extending the life of operation. 13. Energy saving on connected loads by properly regulated power output. This unit is g combinotion of vorious Functional Blocks that facilitates management of un-man Telecom Sites and a complete standalone site manager which could be ordered with various combinations,to suit every site need. 4.2 Proposed 30 Features - Summery of the Techniques The development of the stabilizer system will be included with 30 features that specially designed for the telecom applications. The research paper will discuss the technical design, implementation and expected outcomes in detail in the Chapter 5 under Theoretical Development and the summery of the same is tabulated as follows. 22 5 LIBRARY • . i y Feature Methodology Outcome 1 Expanded input voltage window Higher rated windings/ power circuits designed on extreme case scenario Possible to operate under very low or higher voltage 2 Fast respond for voltage correction Small stepped servo transformer Load feels minimum of input power changes by maintaining proper RMS output. Increasing speed and performance of the synchronous servo motor 3 Short adjustment time Servo motor with high starting torque 4 Stops immediately after switching off & start back in very short time Self-starting synchronous motor with permanent field 5 Select best available phase Phase selector with single phase servo that possible to feed from all 3 phases Higher reliability in Operation with the best available phase 6 Non distorted sine wave output Static line conditioner & Isolation Transformer in series to the system Load receiving true RMS supply from the distorted input power 7 Prevent from RF & EM interference RFI/EMI/EMC/EFT filter blocks Load receiving quality supply from the distorted input power 8 Reducing both common mode and differential mode noise emissions Reduce high frequency emissions from inverters, etc 9 Precise degree of rotation motion System amplifier with closed loop control circuit Minimum of output voltage error 10 Protection from transient voltage surge or spikes MOVs across the input Precious protection from Voltage surge & spikes 11 Protection from Lighting and Surge Class-B & C surge diverters p laced properly Precious protect ion from Lighting and Surge 12 Short circuit protection Properly selected fuses Precious protect ion for equipments on short circuit 13 Over Voltage and Under Voltage protection Electronic relay monitors the output and act ivated to disconnect input. Also actuate audible or visual alarms Protections for the unit under higher or lower vol tage when exceeds the design limits 14 Protection from overloading or short circuit conditions High quality MCB incorporated to the system Quick isolation of incoming supply under overloading or short circuit conditions 23 15 Manual or Emergency by-pass Push button wired also with by pass path from income to load. Provision to by pass in case of emergency or maintenance time 16 Protections from harmonic currents & improve power factor Line reactors used Reduce harmonic currents, spikes, fault currents & save on the electricity costs 17 Output reactors/ chokes Output reactors/ chokes Protect motor from over voltage failures associated with long cable runs, Reduces motor temperature &. audible noise 18 Higher reliability & trouble free performance of servo motor Self lubricating carbon roller assemblies on a fiber glass carrier board Long life of operat ion without trouble or worn out of brushers 19 Minimize losses in operation Wound with heavy section of multi strips electrolytic copper and special lamination Minimize copper losses & iron losses 20 Overall M&E equipment management Main Controller panel incorporate with equipment in automatic operation Gen, AC, Fan automatical ly select only when required 21 Basic status monitoring of the unit Analog voltmeters, ammeters, phase indicator lamps, etc on the panel front On site reference on the unit operation and conditions of power 22 Remote Monitoring of the unit status The dry connectors of the BTS used to extend the alarm to the NOC with relays operated when output tripped off due to exceeded voltages. Monitoring the failures of the unit remotely and attend immediately for rectification. 23 Auto restart on main return and Startup delay protection Delay timer on startup after transient conditions. Prevent damages to inductive load equipments under transient condit ion 24 Module/ Detachable construction Each module within the unit facilitate for on site dissemble & reconnecting. PCBs compact ly designed and fixed in such a manner that it can be easily removed and reconnected. Easy customization to suite variety of installation, transportation & replacement conditions 24 25 Proper ma in tenance at tent ion On site instructions on the routing main tenance and scheduled visits for the same. On site minimum spare stocks for easy replacement . Extended lifetime of the unit with regular main tenance & attentions. 26 Enclosure construction for outstation use IP 54/55 protect ion against solid/ liquid ingress, louvers for ventilation and the openings are covered with neoprene gasket for dust proof Higher reliability in Operat ion with long life. Prevents moisture and contaminants in harsh environments 27 Electronic components for long hours trouble free operat ion Electronic components used of high quality and properly soldered for long hours of continuous trouble free operation. Internal fans for forced ventilation. Higher reliability in Operat ion with long life. 28 Lowest in Weight & facilities for movement / transportation Use lest weight components for the construction. Include lockable rollers for movement & handles for carrying with connect ing supporters. Easy transportation & movements 29 Low noise operat ion with minimum friction Gear arrangements are properly al igned to give smooth, free low noise operat ion with minimum friction. Used self lubricants on moving parts with auto refilling back once empty. Noise free & environmental friendly operat ion 30 Energy-efficient motors Energy-efficient motors used. Lengthening the core and using lower-eiectrical-loss steel, thinner stator laminations, and more copper in the windings reduce electrical losses. Improved bearings and a smaller, more aerodynamic cool ing fan further increase eff iciency. Lowest in the cost of operat ion on electricity with higher ef f ic iency on motor operat ion. Table 4.1: Summery of the Proposed 30 with techniques & outcomes. 25 Chapter 5 THEORETICAL DEVELOPMENT 5.1 Development Areas The proposed development of Voltage stabilizing system will be commenced through the following steps and final output will completely be solution oriented and will best fitted with the real Telecom operational conditions having many & different environment/ power abnormalities. The theoretical development will be commenced in the following 4 steps. 1. Problem Identification & Categorization: Identify the existing equipment arrangements & environmental abnormalities in various Radio base station sites and limitations associated with the existing arrangements. 2. Analyze the problem, solutions & related issues: Identify & analyze the problems, limitations & solutions associated with the sites in practice. Categories those RBS sites to few "RBS models" which best represent the overall environment & power situations, in order to implement the solutions in more simple way. 3. Technical approach for the proposed solutions: Identify design parameters & theoretical methodologies which need to be considered for the development of proposed voltage stabilizing system and detailed discussion on technical implementations of the real solutions for each RBS models. 4. Improve & enhance the performance of the voltage stabilization system: Analyze & design completely telecom oriented voltage stabilizing unit for the given applications with more advanced performance & features. 26 5.2 Problem Identification and Categorization 360 of RBS sites in operation Island wide 110 of RBS sites in Colombo area 250 of RBS sites in outstations 333 of CEB/ LECO power available sites 27 of CEB power not available sites 19 of Highly under voltage sites (Gen operate 5 - 1 0 Hrs per day) 124 of Voltage marginally stable sites (Gen operate less than 4 Hrs per Day) 190 of Voltage perfect & total Main powered sites 13 sites under construction with CEB power pending 14 of full day Generator running sites (Transformer proposed) Voltage stabilization Solution Possible • 19 sites of Voltaae hiahlv dropped (130- 185V, lph) • 124 sites of voltage marginal (185 V above, lph) Voltage stabilization Solution not possible or not required • 190 sites of voltage perfect • 13 sites of CEB oendina • 14 sites of separate transformer proposed Table 5.1: Categorization of RBS sites considering power & voltage constrains The categorization of RBS sites considering power & voltage constrains can be summarized as above (Reference: RBS implementation details of Lanka Bell Limited as on Sep. 2008). Out of the above 360 sites, Generator operation period at 46 sites are very high (categories underlined in above Table 5.1) and those are due to very low voltage, power unavailability and pending CEB connections. Reducing the highest Generator operation at those 46 sites is possible only at 19 sites, which is having the commercial power with low voltage. Direct solutions are not possible at other 27 sites. Out of the 27 sites, 14 sites need separate transformer (with huge Capital cost, listed in table 2.2) or need to run only with Generator (with huge operational cost, discussed in Chapter 6) as the CEB is unable to extend the power from the nearest Distribution transformer due to the huge distance up to the site. 5.3 Analyze the problem, Solutions & related issues Referring the above site conditions, the voltage stabilization solutions can implement in different stages for the 19 sites, as the site & related equipment arrangements are different. Hence, localized solution can be given with few modifications to the existing electrical system. This is more cost saving as each solution is best fitted to the individual site and modifications are also case by case basis, which will avoid generalizing solutions with higher cost. The low voltage range & occurring time period were obtained at the above 19 sites after several on site observations and the figures are listed in Table 5.2, along with the other important parameters considered. The sites are categorized under the operational Cluster basis (7 clusters plus Colombo main center for Lanka Bell) and the table also mentioning the available types of the Generator, ATS panel and the power capacity of each site, along with the observed time period of the under voltage as on the nature of the power supply in the given area. Most of the existing ATS (Automatic Transfer System) of the generator are designed to operate above 185V, lph and with low voltage; the coils of the contactors & relays will tend to burn out due to high current. In addition, the power distribution panels & control power systems also designed to operate above 185V as for the general use. Hence, the above panels need to be modified to operate in under voltage with 48V DC operated contactors (powered by RBS DC battery banks) to make the operating voltage down to around 150V. However, some of the ATS panels are electronic module type and panels can not be modified. Those need to be replaced with new ATS designed by us for low voltage applications. 28 CASE NO CLUSTER & RBS NAME GEN TYPE ATS TYPE POWER SUPPLY UNDER VOLTAGE GEN RUN TIME SOLUTION POSSIBILITY Kandy 1 Hatharaliyadde 1 Cummins Cummins 30A, 1ph 130-140 Continuously YES 2 Dambulla 2 Cummins Cummins 30A, 1ph 175-190 4PM-10PM YES 3 Wahakotte Pending supply by CEB & already requested. NO 4 Karagahathanna No CEB. Gen 24 hrs Running & Transformer needed NO 5 Madamahanuwara Mo CEB. Gen 24 hrs Running & Transformer needed NO 6 Galaqedara No CEB Gen 24 hrs Running & Transformer needed NO 7 Katugastota No CEB. Gen 24 hrs Running & Transformer needed NO 8 Ankumbura No CEB. Gen 24 hrs Running & Transformer needed NO 9 Kawduoelella No CEB Gen 24 hrs Running & Transformer needed NO 10 Nildandahinna No CEB Gen 24 hrs Running & Transformer needed NO 11 Rikillaqaskada No CEB Gen 24 hrs Running & Transformer needed NO 12 Dodanqaslanda No CEB, Gen 24 hrs Running & Transformer needed NO Rathnapura 13 Kuruwita 3 FG Wilson ATI 53 30A. 1ph 140-160 24Hr CEB YES 14 Parakaduwa 4 Temast Hayles 30A. 1ph 160-170 6PM-11PM YES 15 Neugala 5 Temast Hayles 30A, 3ph 160-130 5PM-11PM YES 16 Niwithigala No CEB, Gen 24 hrs Running & Transformer needed NO 17 Ingiriya Pending supply by CEB & already requested. NO 18 Avissawella Pending supply by CEB & already requested NO 19 Endana Pending supply by CEB & already requested NO 20 Thalduwa Pending supply by CEB & already requested NO 21 Hettimulla No CEB Gen 24 hrs Running & Transformer needed NO 22 Ratnapura No CEB Gen 24 hrs Running & Transformer needed NO 23 Kiriella Pending supply by CEB & already requested. NO Monaragala 24 Mahaoya 6 FG Wilson TITO 30A, 1ph 150-155 Continuously YES 25 Batticaloa 7 FG Wilson T170 30A. 1ph 160-165 Continuously YES 26 Badalkumbura 8 FG Wilson T170 30A. 1sh 170-175 Continuously YES 27 Medaqama 9 FG Wilson TT70 30A. 3ph 170-180 Continuously YES 28 Wellawaya 10 Temast Hayles 30A. 1oh 170-175 Continuously YES 29 Ridipana No CEB, Gen 24 hrs Running & Transformer needed NO Matara 30 Kananke 11 FG Wilson TI70 30A. 1ch 150-155 Continuously YES 31 Rilagala 12 FG Wilson T170 30A 1ph 160-170 4PM-10PM YES 32 Gandara 13 FG Wilson T170 30A. 1oh 160-170 4PM-10PM YES 33 Henaggegoda Pending supply by CEB & already requested NO 34 Gatebarukanda Pending supply by CEB & already requested NO 35 Mapalagama No CEB. Gen 24 hrs Runninq & Transformer needed NO 36 Morawaka Pending supply by CEB & already requested NO 37 Kamburupitiya Pending supply by CEB & already requested NO 38 Yakkalamuila Pending supply by CEB & already requested NO Anuradapura 39 Minneriya 14 FG Wilson TI70 3 OA. 1ph 165-180 Continuously YES 40 Galenbindunuwew 15 FG Wilson T170 30A. 1ph 170-180 5PM-10PM YES 41 Nochchiyaqama 16 Hayles Hayles 30A, 1ph 170-180 6PM-10PM YES 42 Jayanthipura Pending supply by CEB & already requested NO Kurunegala 43 Rideegama 17 FG Wilson TI7Q 30A. 1ph 160-195 Continuously YES 44 Polpithiqama 18 FG Wilson ATI63 30A, 1ph 160-170 Continuously YES 45 Maspotha 19 FG Wilson T170 30A 1ph 170-180 5PM-10PM YES 46 Karuwalagaswewa Pending supply by CEB & already requested NO ' I I I I ' I Table 5.2: Details of RBS sites having highest Gen running & possibility of the solutions In summary, the above findings will be used to identify the solutions required & best fitted to those sites on individual basis, rather applying general solutions. Considering all the above factors, the sites can be categorized to the following 5 models to generalize the solutions. RBS Model Characteristics of the RBS site New ATS panel Modify ATS panel 2 x 3 KVA AVS for A/Cs 8 KVA AVS for main input 0 RBS site with under voltage above 185V and almost stable voltage. - - - - 1 RBS site with under voltage 170 - 190V and easy access to the site. - - - V 2(a) RBS site with under voltage 150 - 185V and existing ATS can be modified. - V V - 2(b) RBS site with under voltage 150 - 185V and existing ATS cannot modify. V - V - 3 RBS site with under voltage bellow 150V and frequent voltage fluctuations. V - V V 4 RBS sites with no CEB supply & operate on 24hr Generator power. - - - - Table 5.3: Categorization of RBS sites to 4 models considering existing site conditions The sites are categorized with the voltage in 150 - 170V range need only 2 of 3 KVA Stabilizers for two A/Cs and sites with voltage above 170V can be operated only with 8 KVA installed at main incoming line with suitable ATS arrangements. The sites are categorized with the voltage bellow 150V, need both 2 x 3 KVA (two A/Cs) & 8 KVA (main incoming point) as step-wise voltage improvements is much more reliable and further voltage dropping with connected loads can be avoided with this duel arrangement. 30 By referring the manufacturer's recommendations for standard Radio base station, the following technical parameters can be fixed for the telecom equipments inside the room [9], [23]. Item Range Short term: -10°C to +40°C, Long term: 16°C to 26°C Temperature (Measured when no solar radiation. Under solar radiation, the maximum values should be 3°C lower) Temperature change rate <= 3°C/min Relative humidity 45% to 85% Altitude <= 4,000 m Air pressure 70 kPa to 106 kPa Solar radiation <=1,120 W/m2 Heat radiation <= 600 W/m2 Wind speed <= 67 m/s Input voltage for Rectifier 170- 250Vac Input voltage for BTS rack 48Vdc +/- 5% Input voltage for A/C unit 220 Vac +/- 10% Input voltage for ATS unit 170 - 250Vac Input voltage for Flourscent 190 - 250Vac Input voltage for Exaust Fan 160 - 250Vac Input voltage for panel indicators 220 Vac +/- 10% Table 5.4: Environmental requirements of the standard RBS equipments The proposed equipment arrangement & modifications at the Telecom Radio Base Station can be shown as follows. Commercial Main power 1 ph 30A ATS (modified) 1 ph 12.5kva Generator SYMBOLS Modified Automatic Transfer Switch (ATS) panel for under voltage operation Base Station Equipments PDF A V S BKva 1ph AVS 3kva 1ph AVS 3kva 1ph 3ph -| 1 A/C unit 1 • j I Alarm panel 1ph 1ph H I A/C unit 2 —I I Exaust fan I I Light & Other Rectifier Rack Automatic Voltage Stablizer (AVS) 140 - 250 Vac Fig 5.1: Proposed arrangement of equipments inside the RBS site In addition to the above considerations, the following areas need to be considered before the design of complete system for the voltage stabilization. 1. Input power conditions at each site locations to select the range of stabilization required. 2. Output power accuracy to feed the connected equipments for smooth operation. 3. Protection requirement as per site conditions & equipment specifications. 4. Environmental parameters to design the systems for long lasting operation. 5. Installation, Monitoring, trouble'shooting & maintenance facilities. 6. Energy saving & loss reduction design for operation cost reduction. Hence, the technical approach for the complete design has to consider all the above parameters in order to implement the complete solution which best fit to the individual site requirements (each RBS Model can be considered), after several on site analysis of actual conditions. < 32 5.4 Technical approach for the proposed solutions The technical approach of designing the proposed system is having the following 3 phases. 1. Define 3 of the RBS Models (which needs the solutions right now) with their characteristics & operational requirements. 2. Identify the design requirements in general for above RBS model. 3. Propose the theoretical methodology of the AVS design of above RBS models. 5.4.1 Define the RBS Models The characteristics & operational requirements of each RBS Model can be listed as follows, along with schematically diagrams of the equipments arrangements and detail specifications will be discussed in the table 5.5. RBS Model 1 Ai'CI <• AIarm A.Z2 r E/Fs!! Res Ugifcts Fig 5.2: Schematic arrangement of Model 1. • Input voltage in 170 - 190V, 1 ph range with short durational variations. • Access to the site is easy & environmental conditions are stable. • Sites are located relatively closer to the Distribution transformer. • RBS room equipped with more complicated electronic equipments and operates as combinations of CDMA, WiMax, Proxi and as backbone center. PDF : - 1SGV) Sky a AVS CEE O - f ATS (Exstssg) RBS Model 1 33 RBS Model 2(a) PDF J*V5 AVS ( I S O - 185V) ATS i'v'otfffsedi:: —| ] — A'CI + ASarra j | A c : - E F » - Rsc. l ights RBS Model 2(a) Fig 5.3: Schematic arrangement of Model 2(a). • Input voltage in 150 - 185V, lph range with considerable voltage variations. • M&E equipments (ATS & PDF accessories) can be modified for low voltage. • Access to the site is difficult & environmental conditions are also unstable. • Sites are located far away to Distribution transformer & line averagely loaded. • RBS room equipped mainly with CDMA equipments and simple operation. RBS Model 2(b) PDF 3icv« AVS (150- 1S5V) CES —| |— AC1 + Alans j | AC2 + B ' F » ATS (New) Rec. RBS Model 2(b) - Ugihts Fig 5.4: Schematic arrangement of Model 2(b). • Input voltage in 150 - 185V, 1 ph range with frequent voltage variations. • M&E equipments (ATS & PDF contactors & relay controls) are associated with electronics onboard card, sealed type & can not modify for low voltage. • Access to the site is difficult & environmental conditions are highly varied. • Sites are located faraway to Distribution transformer & line is loaded. • RBS room equipped mainly with CDMA equipments and simple operation. 34 RBS Model 3 PDF 3kv» AVE :Be : 150V) CHS Skvs AVS - o - r ATS (New) RBS Model 3 -| j — A?'€1 + Alarm - j | A. C2 * E/Fjp Reo Fig 5.5: Schematic arrangement of Model 3. • Input voltage below 150V, l ph range with huge voltage variations. • M&E equipments (ATS & PDF accessories) are associated with electronic controls with onboard card/ sealed type & can not modify for low voltage. • Access to the site is difficult & environmental conditions are also unstable. • More additional protections required for power & environmental abnormalities. • Sites are located faraway to the Distribution transformer & line is loaded. • RBS room equipped mainly with CDMA equipments and simple operation. 5.4.2 Identify the Design Requirements for each RBS Model This is to identify the design parameters in terms of Electrical, Environmental, Protection, Monitoring & Equipment construction requirements for each of the RBS Models in detail. The following data were obtained after several site surveys. Design Requirements Model 1 Model 2(a) Model 2(b) Model 3 1 Electrical Data 1.1 Rated input voltage 170- 190V 150- 185V 150- 185V Below 150V 1.2 Input voltage correction 230V - 26% 230V - 35% 230V - 35% 230V - 40% 1.3 Rated frequency 50 Hz 50 Hz 50 Hz 50 Hz 1.4 Mains input capability 10KVA 7.5KVA 7.5KVA 8KVA 1.5 Rated output voltage 230V+/-1% 230V+/-1.5% 230V+/-1.5% 230V+/-3% 1.6 Accuracy of adjustment 99% 98.5% 98.5% 97% 1.7 Output waveform true RMS Follow input Follow input Follow input 1.8 Response time 0.05 Sec/V 0.05 Sec/V 0.05 Sec/V 0.05 Sec/V 1.9 Efficiency >95% >93% >93% >90% 1.10 Rated current/ power 8.5 kW 6.5 kW 6.5 kW 7 kW 1.11 Input Power factor 0.85 0.85 0.85 0.85 1.12 Loading balance balanced unbalanced unbalanced unbalanced 35 1.13 Loading time continuous short-time short-time short-time 1.14 Rated short-time current standard standard standard standard 1.15 Overload Capacity 110% 125% 125% 115% 2 Environment Conditions 2.1 Ambient temperature 27C 25C 25C 20C 2.2 Relative humidity 65% 50% 50% 40% 2.3 Installation altitude Low Medium Medium High 2.4 Climatic surroundings Good Average Average Bad 2.5 Bedewing possible No No Yes Yes 2.6 Pollution possible Yes Yes Yes Yes 3 Protection Requirements 3.1 Thermal-magnetic overload Required Required Required Must 3.2 Main on/ off switch Required Required Required Must 3.3 Transient voltage Surge Required Required Required Must 3.4 Phase loss sensing Must Required Required Must 3.5 Automatic output delay on system Must Required Required Must 3.6 built in IP enclosure Required Must Must Must 3.7 Installation location indoor indoor indoor indoor 3.8 Leakage current Standard Standard Standard Standard 3.9 Earth fault Standard Standard Standard Standard 3.10 Enclosure ventilation forced forced forced forced 3.11 Bypass-circuit options Standard Standard Standard Standard 3.12 Isolation transformer Required No No Required 3.13 EMI interference filter Required No No Required 3.14 RFI interference filter Required No No Required 3.15 Output fuse No No No Required 3.16 Stall protection for Servo Motors Standard Standard Standard Standard 4 Equipment Construction 4.1 Available volume 4.2 Enclosure construction steel sheet stainless steel stainless steel stainless steel 4.3 Enclosure mounting stationary moveable portable portable 4.4 Weight of the AVS unit Allowed Average Average Minimum 4.5 Reliability (MTBF) Standard Standard Standard Standard 5 Monitoring Facilities 5.1 Phase indication Standard Standard Standard Standard 5.2 Ampere meter Standard Standard Standard Standard 5.3 Voltmeter Standard Standard Standard Standard 5.4 Remote alarm Required Optional Optional Required Table 5.5: Design requirements of the RBS Models in detail 36 5.4.3 Theoretical methodology of the design The customized design of the voltage stabilizing system should consider the above 3 Models and the final design has to be well fitted with the design requirements. The following areas need to be considered for the development. 1. Design of the Servo Motor system 2. Design of the Autotransformer of the stabilizer 3. Design of the control system of the stabilizer 4. Achieving the highest accuracy of the output Voltage 5. Incorporate protections for the system 6. Maintenance & Monitoring facilities 7. Energy Efficiency, loss reduction & power savings 8. Construction of the unit for rough environment use 5.4.4 Various design technology used in Voltage Stabilizers Various technologies can be seen on voltage stabilization and the selection will mainly depend on the particular application [5]. Each technology is having different advantages over the other. So, proper selection is much important for the proper operation. The detail design procedures and design advantages/ disadvantages can discuss as follows. 5.4.4.1. Electronic Servo / Electro - Mechanical Design For most applications, Servo Electronic -Electro Mechanical Ranges have proved to be a very reliable and cost-efficient voltage stabilization solution, being able to accommodate an input voltage swing of in excess of 40% whilst still delivering an accuracy of 1% on the output. Comprising a transformer having its secondary winding connected between the mains supply and the load, the primary voltage is automatically controlled through a motor driven variable transformer - ensuring a continuous, smooth and very stable output voltage. 5E L I B R A R Y Fig 5.6: Circuit arrangement of Electronic Servo / Electro - Mechanical Design High Voltage / Transient Spikes are normally limited by the inclusion of 'Spike Clippers'. Such clippers typically limit transients to twice the peak voltage of the supply. To reduce the spikes to totally harmless levels it is often necessary to fit additional Spike Attenuation protection. While Electronic Servo stabilizers do contain some moving parts, experience over many years in some of the most demanding power conditions has proved the design to be a very reliable method of delivering voltage regulation with only a low-level of ongoing maintenance required being deliverable by universally readily available skill sets. The long-life expectancy, compact size and low cost of ownership makes servo electro mechanical stabilizers economical solutions for a wide variety of applications in industry, commerce, mining, aerospace, computing and telecommunications. Design Advantages Design Disadvantages Size and weight advantages over other methods Moving parts requiring limited maintenance Fast speed of response to voltage changes Lower speed of response compared to solid state designs Very competitively priced Negligible output waveform distortion Not Frequency dependent Will attenuate voltage spikes if required Unaffected by load or power factor changes Low cost of ownership with ease of serviceability Endurable, with long life expectancy Table 5.6: Advantages & Disadvantages of Electronic Servo / Electro - Mechanical Design 38 Due to the general popularity of this method of voltage stabilization and the high demand for models between 1 kVA and 500kVA it is often possible to purchase on short lead delivery times. 5.4.4.2. Solid State Saturable Reactor Design With no moving parts, solid state design based systems utilize the latest in IGBT control circuitry delivering a very high speed of response and output accuracy maintained to ±0.5%. Since all components are of electronic design, they are virtually maintenance- free Fig 5.7: Circuit arrangement of Solid State Saturable Reactor Design Solid state based systems are ideal solutions for equipment that must have output voltage accuracy better than 1%. Design Advantages • Design Disadvantages High speed of response to voltage changes Usually less price competitive to Servo Electronic design Output voltage accuracy typically in 0.5% range High weight to kVA ratio to electronic servo designs No Moving parts - virtually Maintenance Free High efficiency Not Frequency dependent Output voltage not collapse on overload or sever input voltage drop Low output waveform distortion Unaffected by load or power factor changes Table 5.7: Advantages & Disadvantages of Solid State Saturable Reactor Design 39 5.4.4.3. Magnetic Induction Solid State Design The design technology utilizes a simple, highly reliable, rotor and stator design principle to increase or decrease the magnitude of the voltage in a series transformer winding, which thereby delivers and maintains a constant voltage. Fig 5.8: Circuit arrangement of Magnetic Induction Solid State Design Unlike the Servo-Electro Mechanical design, this technology does not require carbon brushes and there is no contact wear. As a result Magnetic Induction based stabilizers are highly reliable and can be viewed as virtually maintenance free solutions. Design Advantages Design Disadvantages High output voltage accuracy Less price competitive when compared to Servo Electronic design High reliability Virtually Maintenance Free with no contact wear or requirement for carbon brush replacement Table 5.8: Advantages & Disadvantages of Magnetic Induction Solid State Design Available for only larger Three Phase applications above 200 kVA, available in two ranges of Magnetic Induction based voltage stabilization solutions -Air Cooled and Oil Cooled solutions. 40 As standard Magnetic induction based stabilizers sense on a single phase and correct for voltage fluctuations simultaneously across all three phases, being suitable for unbalanced loads up to 30%. This is on the other hand offer independent phase sensing / control and are suitable for unbalanced voltages and loads up to 100%. The Oil Cooled models offer more efficient cooling and as a result tend to be smaller in physical size compared to their air-cooled model. Oil cooled stabilizers are ideal for deployment in very humid environments. 5.4.4.4. Ferro-Resonant - Super Isolation Solid State Design Based around a highly reliable and endurable Constant Voltage Transformer (CVT), super isolation design based systems (Single Phase AC Power Conditioners) are able to tolerate very wide input fluctuations, even when input voltage drops as low as 40%, the output voltage will be maintained at nominal voltage ±5%. With no moving parts and no electronic control circuitry there is no need for maintenance and is virtually an install and forgets solution. The design can withstand high instantaneous overloads and is able to suppress lightning induced spikes and surges. Compact in size and quiet in operation, this design has the inherent ability to withstand a ride-through even when there is a very short power failure, maintaining voltage for 3msecs. This feature is exceptionally useful for sensitive electronic equipment when there are frequent short breaks or severs voltage dips. Fig 5.9: Circuit arrangement of Ferro-Resonant - Super Isolation Solid State Design 41 Design Advantages Design Disadvantages High speed of response to voltage changes Not generally competitive in ratings above 10 kVA Output voltage does not collapse on overload or sever input voltage drop High weight to kVA ratio compared to other stabilization methods Attenuates voltage spikes Frequency dependent - not ideal for where severe frequency variations are an issue Competitively priced AC Power Conditioning solution for ratings of 5 kVA or below No Moving parts - virtually Maintenance Free Highly reliable with extremely high MTBF performance Inherent ride-through ability Endurable, with long life expectancy Table 5.9: Advantages & Disadvantages of Ferro-Resonant - Super Isolation Solid State Design 5.4.4.5. Electronic Tap Changing Solid State Design The Electronic Tap Changer design principle operates by automatically selecting one of a series of taps on an auto transformer. © — r 1 © r "". i fttJ*. , , 0«fcj<* ® i - T T ® Fig 5.10: Circuit arrangement of Electronic Tap Changing Solid State Design 2 L I B R A R Y ^ 42 l r < D i d Design Advantages Design Disadvantages Most competitive in price for 2 kVA and below Poor output voltage accuracy - typically no better than ± 5% High Efficiency Generally / historically deliver a low MTBF (Mean Time between Failures) Negligible output waveform distortion No Moving parts - virtually Maintenance Free Table 5.10: Advantages & Disadvantages ot Electronic Tap Changing Solid State Design 5.5 Design of the Servo Motor system 5.5.1 Aim of the design The aim of the design is to obtain completely the dimensions of all parts of the machine to furnish these data to the manufacturer. The design should be carried out based on the given specifications and optimize basically to achieve the lowest cost, lowest weight, reduced size and better operating performance [6], The design is worked out by resorting to various approximation methods based on different formulas, equations, laws, etc. In addition, the design of an electrical machine, must emphasis on lowering cost by saving the materials and reducing labor consume operations to its manufacturer. The design should be satisfactory with respect to electrical strength, mechanical ruggedness, dynamic and thermal resistance of windings in event of short circuit. 5.5.2 General Design Procedure Following design procedure is used in general for design of servo motor system [6]. • Referring the given specifications of the machine, choose proper materials of conducting, insulating and magnetic parts. The properties, availability and cost of those materials are considered under this stage. • Basic design parameters such as specific magnetic loading, specific electrical loading, etc are assumed suitably, keeping in view the advantages and disadvantages of higher values of specific loading. • Design is initiated with the calculation of various dimensions of magnetic and electric circuit, using various design requirements developed. 43 • Based on the calculated dimensions of the various circuits of the machine, performance of the machine under no load and loaded conditions is predetermined. The temperature rise of the machine, which is of utmost importance is then determined from the calculated values of total losses and the cooling system adopted. • Calculated performance of the machine is compared with the limiting performance values or customer's requirements. If the performance is not satisfactory, the basic assumption of design parameters needs to be changed, so as to bring the final design closer to the objective. 5.5.3 Constructional & Operational characteristics Automatic Voltage Stabilizer is an Auto Wound Transformer which is having helical coils mounted on a conventional laminated core [5]. Carbon Rollers assembled on a fiber glass carrier board traverse the length of the Coil Track. These rollers are electrically connected to the output terminals and as they are driven over the track, a variable voltage is obtained. The variations of more than ± 1% of the rated output voltage of the stabilizers are sensed through solid state relay which sends signals to the controlling servo motor which further drives the roller mechanism in such a direction so as to increase or decrease the voltage and stabilize it to the rated output voltage. Servo motor is responsible for producing mechanical changes from an electromagnetic actuating device.-It is very special type device that is used to achieve a precise degree of rotation motion. Motor must be able to respond accurately to signals developed by the system amplifier. It is also capable of reversing direction quickly when a specific signal polarity is applied. Also, the amount of torque developed by a servomotor is quite high. •o •o Fig 5.11: Schematic diagram of Servo motor system 44 (A1 - Control unit, M - Servo drive, T1 - Variable autotransformer, T2 - Booster transformer) Transformer Core can be manufactured with laminations from Cold Rolled Grain Oriented (CRGO) steel. These laminations are manufactured for distribution and power transformers from 10 KVA to 200,000 KVA and can be mitred (45° angle), V- notched. These laminations are also annealed (to reduce stresses and therefore the watt losses as well as the no load current). But CjWtGA 8ru*tt Cuntfil Takeoff Aitemblr Surface Lamln mod StmstC&e Fig 5.12: Standard assemblies of Servo motor Auto volt variacs are designed for heavy duty trouble free operations. All components are designed to give maximum life to the unit under extreme operating conditions. Automatic Voltage Stabilizers are constructed of electrically and mechanically reliable components. Variable toroidal transformers with motor drive, booster transformers, and electronic control units are simple and robust components which assure a long service life. A self-starting synchronous motor with permanent field is used for the servomotor. The high starting torque of this motor allows relatively short adjustment time; it stops immediately after switching off, whereby the permanent field does not require a mechanical brake system. 45 5.5.4 Specifications & Design parameters The initiation of the design of servo motor requires a specifications of main data like output in KVA, line voltage, power factor, frequency, number of phases, type of connections, temperature rise of windings & core, rated speed, overload capacity, etc. Those data can directly be obtained from the table 5.5. However, certain specifications of performance are usually taken with the experience, such as no load loss, full load current, short circuit current, percentage regulation, etc. 5.5.5 Selection of Materials The basis of all materials science involves relating the desired properties and relative performance of a material in a certain application to the structure of the atoms and phases in that material through characterization. The major determinants of the structure of a material and thus of its properties are its constituent chemical elements and the way in which it has been processed into its final form [7]. Electrical materials used in construction of all machines can be classified in to 3 groups, named Conducting, Insulating and Magnetic materials. The performance, cost and physical characteristics of the machine will depend on the quality of those materials. If low grade materials are used, the machine would too heavy and costly. Hence, the best practice is to select the proper materials, so as to improve the efficiency, reduce the size, weight and cost with increase of the reliability of the operation [6], [8], The conducting materials selected should possess the following requirements. • Lowest possible resistivity • The least possible temperature coefficient of resistance • Adequate resistance to corrosion. • Adequate mechanical strength, especially high tensile strength. • Good weldability and solderability which ensure high reliability and low electrical resistance of the joints. • Property of reliability and drawability. 46 The insulating materials selected should possess the following requirements. • High insulation resistance • High dielectric strength • Low dielectric losses and low dielectric loss angle • No attraction for moisture • Capability of withstanding without deterioration a repeated heat cycle • Good heat conductivity • Sufficient mechanical strength to withstand vibration and bending • Solid materials should have a high meting or softening point • Liquid materials should not evaporate or volatile. The magnetic materials selected should possess the following requirements. • High magnetic permeability so that even a weak current flowing in the electromagnet can set up large fluxes in its core • High electrical resistivity, in order to decrease the eddy current losses occurring in the magnetic materials. This can be achieved by building the core with thin laminations, insulated from each other by varnish. At higher frequencies the thickness of the laminations must be further reduced. • The hysteresis loop of the magnetic material should be narrow and must have a small area, in order to reduce the hysteresis loss. The above requirements in respect of materials may vary with the purpose and for the servomotor applications, the selection of the materials will solely depend on the assemblies considered in the individual construction. 5.6 Design of Autotransformer in the stabilizer An autotransformer has only a single winding with two end terminals, plus a third at an intermediate tap point. The primary voltage is applied across two of the terminals, and the secondary voltage taken from one of these and the third 47 LIBRARY terminal [5]. The primary and secondary circuits therefore have a number of windings turns in common. Since the volts-per-turn is the same in both windings, each develops a voltage in proportion to its number of turns. An adjustable autotransformer is made by exposing part of the winding coils and making the secondary connection through a sliding brush, giving a variable turns ratio. A failure of the insulation or the windings of an autotransformer can result in full input voltage applied to the output. This is an important safety consideration when deciding to use an autotransformer in a given application. Because it requires both fewer windings and a smaller core, an autotransformer for power applications is typically lighter and less costly than a two-winding transformer, up to a voltage ratio of about 3:1 - beyond that range of a two- winding transformer is usually more economical. Autotransformers are frequently used in power applications in power transmission & in industry to interconnect systems operating at different voltage classes. They are also often used for providing conversions between the two common domestic mains voltage bands in the world (100-130V and 200-250V). On long rural power distribution lines, special autotransformers with automatic tap-changing equipment are inserted as voltage regulators, so that customers at the far end of the line receive the same average voltage as those closer to the source. The variable ratio of the autotransformer compensates for the voltage drop along the line. As with two-winding transformers, autotransformers may be equipped with many taps and automatic switchgear to allow them to act as automatic voltage regulators, to maintain a steady voltage at the customers' service during a wide range of load conditions. By exposing part of the winding coils and making the secondary connection through a sliding brush, an almost continuously variable turns ratio can be obtained, allowing for very smooth control of voltage. 48 5.7 Design of Control system in the stabilizer Control systems span four major areas: temperature, pressure and flow, voltage and current, and motion. Motion control is implemented with three major prime movers: hydraulic, pneumatic, and electric motors. Electronic motion control is a multi-billion-dollar industry. Servo motion is a fraction of that industry, sharing it with non-servo motion, such as stepper motors and variable-frequency systems. A servo system is defined here as the drive, motor, and feedback device that allow precise control of position, velocity, or torque using feed-back loops [10]. Examples of servomotors include motors used in machine tools and automation robots. Stepper motors allow precise control of motion as well, but they are not servos because they are run "open-loop," without tuning and without the need for stability analysis. The most easily recognized characteristic of servo motion is the ability to control position with rapid response to changing commands and disturbances. Servo applications commonly cycle a motor from one position to another at high rates. However, there are servo applications that do not need fast acceleration. For example, web-handling applications, which process rolled material such as tape, do not command large accelerations during normal operation; usually, they attempt to hold velocity constant in the presence of torque disturbances. Servo systems must have feedback signals to close control loops. Often, these feedback devices are independent, physical components mechanically coupled to the motor; for example, encoders and resolvers are commonly used in this role. However, the lack of a separate feedback device does not mean the system is not a servo. This is because the feedback device may be present but may not be easily identified. For example, head-positioning servos of a hard-disk drive use feedback signals built into the disk platter rather than a separate feedback sensor. Also, some applications use electrical signals from the motor itself to indicate speed. This technology is often called sensor less although the name is misleading; the position is still sensed but using intrinsic motor properties rather than a separate feedback device. 49 The input of a servo system serves as the reference element to which the controlled device responds. By changing the input, a command is applied to the error detector. This device received data from both the input source and from the controlled output device. If a correction is needed with reference to the input command, it is amplified and applied to the actuator. The actuator is normally a servo motor that produces controlled shaft displacements. The controlled output device relays information back to the error detector for position comparison. The block diagram representation of the above mechanism is shown as follows. Error Fig 5.13: Block diagram of a servo system controls The design of the control system also considered the other arrangement such as ventilation, protection, etc for the reliable operation. The stabilizer control unit is provided with louvers for proper ventilation and the openings are covered with neoprene gasket for dust proof. Outdoor type stabilizers have IP 54/55 protection against solid and liquid ingress. The control panel is fixed on the top of auto-stat housing to give a compact design. Proper room for removing and repairing the components is provided. The wiring is neatly done and the components are logically arranged for easy phase wise identification and firmly interconnected. The closed loop control circuit is of state-of-the art technology and IC based. All Electronic components used of high quality and properly soldered for long hours of continuous trouble free operation at specified site condition. PCBs compactly ¥ . urn 5 0 designed and fixed in such a manner that it can be easily removed and reconnected. All meters, status / trip indications, control switches etc are placed in front of the control panel and logically arranged phase wise for easy understanding & operation. All indications are of LED type. Cables contractors and windings carrying the load current are properly design for its duty and current rating. Gear arrangements are properly aligned to give smooth, free low noise operation with minimum friction. AC synchronous motor Stepper motor have high torque/power ratio to achieve high efficiency of the stabilizer. The carbon brush of the auto stat function for long period without wearing and a spare brush provided inside the auto stat for immediate replacement. The standard control circuit of Automatic voltage stabilizer can be shown as follows [11]. 51 Fig 5.14: Standard control circuit of Automatic voltage stabilizer 5.8 Achieving the highest accuracy of the output Voltage Voltage fluctuations in power systems can cause a number of harmful technical effects, resulting in disruption to production processes and substantial costs. Theoretically, for any supply line, the voltage at the load end is different from that 52 at the source. Depending on its cause, a voltage change can take the form of a voltage drop having a constant value over a long time interval, a slow or rapid voltage change, or a voltage fluctuation. Voltage fluctuation is defined as a series of rms voltage changes or a cyclic variation of the voltage waveform envelope. The defining characteristics of voltage fluctuations are: • The amplitude of voltage change (difference of maximum and minimum rms or peak voltage value occurring during the disturbance); • The number of voltage changes over a specified unit of time; and • The consequential effects (such as flicker) of voltage changes associated with the disturbances. Until recently, voltage fluctuations in power systems, and at the load terminals, were characterized using factors associated with the peak-to-peak rms voltage change in the power system. The energy of voltage fluctuations, their power spectrum (also called the energy spectrum of voltage fluctuations), and their duration were taken into account when assessing voltage fluctuations. The primary cause of voltage changes is the time variability of the reactive power component of fluctuating loads. Such loads include arc furnaces, rolling mill drives, and main winders — all of which are loads with a high rate of change of power with respect to the short-circuit capacity at the point of common coupling (PCC). Small power loads, such as starting of induction motors, welders, boilers, power regulators, electric saws and hammers, pumps and compressors, cranes, and elevators also can be sources of voltage fluctuations. Other causes are capacitor switching and on-load transformer tap changers, which can change the inductive component of the source impedance. Variations in generation capacity of wind turbines, for example, also can have an effect. Sometimes, voltage fluctuations are caused by low-frequency voltage inter-harmonics. 53 The effects of voltage fluctuations depend first on their amplitude, which is influenced by the characteristics of the power system, and second, on the rate of their occurrence, which is determined by the type of load and character of its operation. Usually, mitigation measures focus on limiting the amplitude of the voltage fluctuations. The technological process is seldom influenced. Examples of mitigation methods for various types of equipment include: • Arc furnaces — Incorporate series reactors (or variable saturation); ensure proper functioning of the electrode control system; segregate and provide preliminary heating of charge. • Welding plants — Supply the plant from a dedicated transformer; connect single-phase welders to a 3-phase network for balanced load distribution between phases; connect single-phase welding machines to different phases from those powering lighting equipment. • Adjustable speed drives — Use soft-start devices. Another way to reduce the amplitude of voltage fluctuations is to increase the short-circuit power with respect to the load power, at the PCC to which a fluctuating load is connected. This can be done by: • Connecting the load at a higher nominal voltage level; • Supplying this category of loads from dedicated lines; • Separating supplies to fluctuating loads from steady loads by using separate windings of a three-winding transformer; • Increasing the rated power of the transformer supplying the fluctuating load; or • Installing series capacitors. Yet another way to reduce the amplitude of voltage fluctuations is to reduce the changes of reactive power in the supply system. This can be done by installing dynamic voltage stabilizers. Their effectiveness depends mainly on their rated power and speed of reaction. By drawing reactive power at the fundamental frequency, dynamic voltage stabilizers produce voltage drops on the supply network impedances. Depending 54 on whether the reactive power is inductive or capacitive, the rms voltage value at the PCC can be increased or reduced. Standard adjustment or accuracy ranges of AVSs are usually arranged symmetrically. For unsymmetrical adjustment ranges, e. g. from + 5 %/ -10 % up to + 10 %/ - 30 %, can be seen. The correction time is determined by the speed of the synchronous servo motor; it is directly proportional to the frequency. In addition, it is affected by the adjustment range. 5.9 Incorporate protections for the system Many protection schemes can be incorporated with the AVS system as per the site conditions and some of them are described below. 5.9.1 Short-circuit and overload protection Carefully selected fuses protect against short-circuits on the output side, thermal or electronically acting trip switches can be provided for overload protection. It should also be noted that the power networks with lower capability, the higher currents occurring at low input voltage result in an additional voltage drop, which the control can no longer equalize. In such cases, detailed information concerning the characteristics of the power network are required for optimal determination, e. g. distance to next transformer station, line cross-section, type of wiring (buried cable, high line), line impedance, short circuit power, etc. 5.9.2 Over and Under Voltage protection The electronic relay continually monitors the output voltage and is activated if the output voltage deviates by ±5% of the preset level. It can be used to actuate audible or visual alarms, or contactors. 5.9.3 Safe Start, Bypass and Circuit Breaker protection Safe start ensures that the output voltage is at a minimum, at the moment of switch-on, before stabilization takes place. 55 Manual bypass switches can be supplied for remote mounting to enable the transfer of load directly to the incoming supply thereby isolating the stabilizer. Input and/or output MCBs or fuses can be fitted when required. 5.9.4 Lightning & Surge Protection Lightning arresters can be used to protect system against induced lightning strikes. Where high voltage transients and spikes are expected to be present on a power system, surge arrestors help to protect sensitive electronics equipment. Additional protection can be added as a safeguard to sensitive loads from Noise, Spike and Transient Protection. 5.9.5 Auto/Manual Control & Emergency by-pass A toggle switch is provided to switch the stabilizer on Auto or Manual mode. In Auto mode the output corrected automatically in closed loop control to give the specified output Voltage. Provision to adjust the set value within the specified is also being provided. In Manual mode an increase decrease push button is provided to adjust the output voltage. Provision to by pass is provided to switch on the output in case of emergency and at stabilizer maintenance time. 5.9.6 Line / Output Reactor Line reactors are used to reduce harmonic currents and thus the power factor of the current drawn by power electronic equipment. At the same time they reduce spikes caused by disturbances on the power supply and they will reduce the level of potential fault currents. Thus as well as protecting the equipment they help save on the electricity costs. In addition, this also helps to reduces surge currents, reduction in harmonic distortion, Improves true power factor and elimination of nuisance tripping from power line spikes. Output reactors, otherwise known as chokes, can also be used on the output side of an inverter drive to protect a motor from over voltage failures associated with long cable runs. The advantages of using an output reactor with a variable 56 speed drive are, Protection of motors from long cable effects, Reduction of output voltage dv/dt, Reduces motor temperature & Reduces motor audible noise. 5.9.7 RFI / EMI Filters RF filters offer a solution to many interference problems in a plant caused by the high frequency emissions from variable speed motor drives and inverters. Type RF filters can prevent drives and inverters from interfering with other sensitive electronic loads by reducing both common mode and differential mode noise emissions. 5.9.8 Sine Wave Motor Protection Filters These filters are for use on the output side of an AC inverter and convert the PWM current from a variable speed drive into a near perfect sine wave at the motor terminals. They are ideal for use when long power cables are necessary and on older motors where the insulation quality may be less than a modern motor. Sine-wave Filters reduce motor insulation stress and eliminate switching acoustic noise from the motor. Bearing currents are also reduced, especially in larger motors above 50 kW. Sine-wave filters prevent disturbing pulses from being transmitted to the motor. Capacitances in screened motor supply cables can otherwise cause high oscillating circuit currents through motor bearings, vaporizing lubricant and causing damage to the bearings. The eddy current losses in the motor can also be minimized in this manner, resulting in a cooler motor and thus extended motor life-time. In addition to protecting the motor, the sine-wave filter also provides protection for the inverter, because the lower pulse load is reflected in lower semiconductor losses. It should however be noted that this filter does not operate in common mode and the leakage currents are not reduced, therefore it does not enable the use of unlimited motor cables lengths. 57 Some of the Benefits are reduces voltage peaks in motor, prevents flashover in motor windings, diminishes over voltages and voltage spikes caused by cable reflections, protects the motor insulation against premature aging, reduces du/dt stresses which Increases motor service interval, lowers the magnetic interference propagation on surrounding cables and equipment which help for trouble-free operation, eliminates acoustic noise in motor which helps on noiseless motor operation and reduces high frequent losses in motor that helps on prolongs service interval of motor. 5.10 Maintenance & Monitoring facilities Regular inspection and preventive maintenance assure reliability and long service life. Some of the important preventive maintenance procedures are as follows. 1. Check all terminals and contacts; pay particular attention to the PE- terminals and their connection. 2. Examine all moving parts for faultless function, position, and fastening. 3. Inspect position and function of limit switches. 4. When necessary clean and lubricate the driving gear assembly. Never lubricate carbon rolls, their axis, or contact paths. 5. When necessary clean carbon rolls and contact path with cloth or paint brush. Surfaces covered with heavy oxide must be cleaned with only non- permanent silver-polish. Immediately wipe again with cloth, soaked in denatured alcohol. Be careful with inflammable materials! Never use emery-cloth or solvents, these materials destroy the contact path as well as the insulation of windings. 6. Check the contact surface of carbon rolls and their pressure visually and manually. The contact pressure of carbon rolls should be about 2-3 kg each. Damaged carbon rolls must be replaced immediately. 7. Check the easy movability of carbon rolls and their holders manually. 8. Keep an inspection book for recording the services at site. Timely replacement of carbon tips and cleaning of the commutator surface of foreign particles and accumulated dust will ensure a considerably long, maintenance free and interrupted life to the unit. 58 The dry contact signals on all type can be extend through the base station signal path and the contact points should be connected directly. Analogue or digital volt/amp meters can be fitted and include phase selector switch on three phase models for the indication of input/output phase voltages or output phase currents. 5.11 Energy Efficiency, loss reduction & power savings Energy is a limited resource for the whole world and need to manage the usage and reduce the wastages. From small user to large industry, the effort & strategies for energy saving is much more important. This is because, the future is unpredictable and if our civilization is to survive; we cannot stray far from the following scenario [12], [13]. 1. We are rapidly exhausting fossil fuels. 2. Future must depend on non-fossil ("renewable" and other) energy sources. 3. Replacement sources probably can supply only a fraction of current usage. 4. Therefore, we must maximize energy efficiency and energy conservation. The following graph clearly explains the gap between the oil discovery and expected consumption of the world market. Hence, every project should deeply consider on the possible energy savings. r«0 1930 1 940 1950 1960 1970 1980 1990 2000 2010 2020 2030 Projected Discoveries Discovery Fig 5.15: The growing gap of the Peak oil discovery and the world consumption 59 Hence, as the energy serving is much important, this development also, considered the possible energy savings on various areas, such as Servo motor efficiency improvement, BTS equipment operation management, etc and the key areas are discussed as below. The key benefits from the energy efficiency are Increased the life of equipments, optimize recycling, Improve operational efficiency, less electricity cost, better plant management, etc. 5.11.1. Energy-Efficiency in Motors Efficiency is an important factor to consider when buying or rewinding an electric motor. Over 70% of all electrical energy consumed in most of the industry is used by electric motors. Improving the efficiency of electric motors and the equipment can drive to save energy and reduce operating costs [14]. Energy efficiency should be a major consideration when purchasing or rewinding a motor, as well as the more common considerations is the purchase price and delivery time. The annual energy cost of running a motor is usually many times greater than its initial purchase price. Energy-efficient motors owe their higher performance to key design improvements and more accurate manufacturing tolerances. Lengthening the core and using lower-electrical-loss steel, thinner stator laminations, and more copper in the windings reduce electrical losses. Improved bearings and a smaller, more aerodynamic cooling fan further increase efficiency. Motor efficiency is the ratio of mechanical power output to the electrical power input, usually expressed as a percentage. Energy-efficient motors use less energy. Because they are manufactured with higher quality materials and techniques, they usually have higher service factors and bearing lives, less waste heat output, and less vibration, all of which increase reliability. This is often reflected by longer manufacturer's warranties. To be considered energy-efficient, a motor's performance must equal or exceed the nominal full-load efficiency values provided by the National Electrical 60 Manufacturer's Association (NEMA) in their publication MG-1. The Energy Policy Act of 1992 (EPACT) required most general purpose motors between 1 and 200 horsepower for sale in the U.S. to meet these NEMA standards by October 24, 1997. However, no such standard applicable in Sri Lanka, but the measures are much valid from the operational point of view. Assuming kWh electricity cost and payback criteria, most motors should be replaced with an energy-efficient model if they operate considerable hours per year in their operations. In general, energy-efficient motors should be considered in the following circumstances: 1. New installations, both separate and as part of packages 2. When modifications are made to a facility or a process 3. Instead of rewinding older, standard-efficiency motors 4. As part of a preventive maintenance or energy conservation plan 5.11.2 Determine Cost Effectiveness of the Motors The cost effectiveness of an energy-efficient motor in a specific situation depends on several factors, including motor price, efficiency rating, annual hours of use, energy rates, cost of installation and downtime, and the availability of utility rebates or other incentives [14]. The following design characteristics are Important when selecting a motor for the particular applications. • Motor Size: Motors should be sized to operate with a load factor between 65% and 100%. The common practice of over sizing results in less efficient motor operation. • Operating Speed: While the average speed of energy-efficient motors is slightly higher than the average speed of standard-efficiency motors for any given size, models of each type are available with a wide range of speeds. Installing a new motor with a higher speed can result in diminished energy savings. It is particularly important in centrifugal pump or fan applications to select replacement motors with a comparable full-load speed. 61 • Inrush Current: Avoid overloading circuits. Energy-efficient motors feature low electrical resistance and thus exhibit higher inrush currents than standard models. The inrush current duration is too short to trip thermal protection devices, but energy-efficient motors equipped with magnetic circuit protectors can sometimes experience nuisance trips during start-up. Energy-efficient motors should be considered for all new installations, replacement of failed motors, or as spares. They are frequently a cost-effective alternative to rewinding, and are sometimes an economic substitute for well- functioning motors in high-duty applications. However, in cases where the faster speed of the energy-efficient motor results in higher energy use without adding to the useful work performed, the energy- efficient motor may not be an economic option. A cost comparison will determine if a motor replacement is cost effective, and an analysis of the whole system-including the driven process, drive train, and controls—can reveal if other changes could provide greater benefits. Energy-efficient motors generally have longer insulation and bearing lives, lower heat output, and less vibration. In addition, these motors are often more tolerant of overload conditions and phase imbalance. This results in low failure rates, which has prompted most manufacturers to offer longer warranties for their energy- efficient lines. Purchasing an energy-efficient motor can dramatically cut energy costs. Energy- efficient motors have a strong track record of high performance, with proven lower failure rates. As with all motors, materials and components can degrade during repair and rewind, reducing the original efficiency level. Insisting that the motor repair shop adhere to recommended quality standards can help maintain motor efficiency at or near original levels. 5.11.3 Energy optimization of the equipments in Telecom operation The standard Telecom base station comprises of various equipments and the energy used by those equipments can be optimized by any of the followings [13]. 62 1. Replace more energy efficient equipment with existing sets 2. Rearrange the equipment (especially Air Conditioners) to get the best operational efficiency in order to reduce the electricity cost 3. Redesign the shelter envelops to minimize the energy used mainly for the cooling purpose 4. Automate the equipment (power & A/C) operation to get the minimum energy use in operation by allowing each set of units to operate only when required 5. Select the power source as Diesel Generator only when the main is not available (Blackout) and voltage is extremely lower by modifying the power equipments to operate under any low voltage with AVS and replace with low voltage sensitive power equipments Out of the following equipments used in telecom site, the energy efficient replacements can be found from the market and proposed to replace. This will benefit as higher energy cost reduction, lower capacity of equipments, extended life of the equipments, improved total operation, etc. The existing equipment and the proposed efficient replacements can be tabulated as follows. Existing Equipment Energy Efferent Replacement HUWEVI BTS 3606 Rack (6Amp) . Newer version BTS rack (4Amp) Emerson PS48300 Rectifier rack Newer version Rectifier rack Split A/C units, 12,500 Btu/Hr (6Amp) Inverter type A/C 9,000 Btu/Hr (IAmp) 12.5KVA Prime Generator 7.5 KVA Standby Generator Bulk Head - Light with bulb (100W) Bulk Head - Light with CFL (7W) 4ft 36W Fluorescent Fixture with magnetic ballast (0.7Amp) 2ft 18W Fluorescent Fixture with electronic ballast & PF cap. (0.2Amp) Emergency Lighting Fixture (75W) Energy saving portable Emergency Lighting unit (40W) 9" Exhaust Fan (2Amp) 9" Energy saving Exhaust Fan [1.2 Amp) Table 5.11: Energy efficient equipment replacements for telecom sites 63 5.12 Technical Analysis on the Power Quality of LV network 5.12.1 Introduction on Power Quality Any power problem manifest in voltage, current or frequency deviations that results in the failure or malfunction or miss operation of equipment [24], Most of the power and telecom system equipments such as Power electronic equipments and Microprocessor base equipments are sensitive to PQ variations. Use of more electronic equipments will results more PQ problems. The voltage plays major roll in the PQ and can be considered as the most ordinary phenomena representing the PQ. The effect of poor PQ are Interrupt supply, Damage sensitive data processing, control & instrumentation equipments, Loss of product quality and efficiency, Light flickering, Over heating of transformers, motors, capacitors, Loss of plant capacity/ life time and mal-operation of tariff meters. 5.12.2 Mathematical modeling of Load level voltage fluctuation Consider the simple model representing a fluctuating load drawing real power P, and reactive power Q, connected to a power system with impedance of resistance R, and reactance X, as illustrated in Fig. 5.16. The voltage VR seen by the customer can usually be regulated by operating the system voltage Vs at a slightly higher value to ensure VR remains at the required value, e.g. 230V for a single-phase system. During steady state operation this can be achieved through the use of automatic tap changers on transformers, line drop compensators and voltage stabilizers. For more rapid changes in load current the operation of such devices is not fast enough in response to effectively regulate the voltage to stay at the required value [24]. The resultant voltage due to the current drawn by the load is illustrated in the phase diagram of Fig. 5.17 where Vs is the supply voltage and VR is the resultant voltage seen by the load at the point of common connection (PCC). 64 Fig 5.16: Simple model of power system Vs Fig 5.17: Phase diagram of supply voltage The complex power drawn by the fluctuating load and the voltage phases can be described by equations (1) and (2) respectively. VR I* = P + jQ (1) V s = VR + I (R + jX) (2) Expanding equation (2) for the voltage phases provides the following VS = V r + (ld-jlq) ( R + j X ) (3) V S = (VR + R Id + X lq) + j(X Id - R lq) (4) Ignoring the phase differences between VR and Vs in equation (4) and equating only the real parts V S = V R + R ID + X LQ (5) Assuming Vs is a very strong supply system, i.e. Vs remains constant regardless of the current drawn by the fluctuating load, for any changes in Id and lq the changes in VR will be as follows 65 0 = AVR + R Aid + X Alq AVR = - (R Aid + X Alq) . (6) (7) Equation (7) can be re-written in per unit, i.e. in terms of the changes in real and imaginary power drawn by the fluctuating load AVR = - (R AP + X AQ) (8) If R is negligible, then the reactance X = 1 / Fault level, leading to equation (9) AVR = - AQ / Fault level (9) Thus, il can be seen that the voltage at the point of common connection is essentially a function of the reactive power variation of the load and supply system characteristics. Note that for low voltage systems where R is considerably larger the real power may also contribute significantly to voltage variations. The above AVR voltage correction range can be corrected by the Voltage stabilizer. £V(R) Fig 5.11: Schematic diagram of Servo motor system (related to voltage correction) (A1 - Control unit, M - Servo drive, T1 - Variable autotransformer, T2 - Booster transformer, VR - resultant voltage seen by the load at PCC, Vi - Corrected voltage to the load at the stabilizer output) The T2 Booster transformer will adjust the VR by changing the topping points of the T1 variable transformer in order to correct and keep stable the load voltage VL. The resultant voltage at the load can be represented as per equation (10) bellow. VL = Vr + AVR (10) Design & sizing of the stabilizer system including the autotransformer, servo motor and the control system to suite the Telecom site requirement can be summarized as follows. The following example calculation can be given. Input voltage = 140 - 240V (AVr = 100V) Output voltage = 230V accuracy 1.5% Power capacity = 7.5 KVA Adjusted speed =10V/sec Select Autotransformer of capacity 7.5KVA, lph with input voltage range 140- 240V, turns 200 and the servo motor selected as 50W, 12V DC with speed suitable for lOV/sec movements by controlled shaft displacement of the rolling brushed on the winding turns. The cross section of the windings can be assumed by the followings manner. AVr (100V) = R (winding) x I (winding) R = pL / A where p - Cu resistivity, L -length, A - cross section of winging. R = AVr (100V) / I (winding) where I = 7.5 x 100 V A / 2 3 0 V = 32.6A The A & R of the windings of the autptransformer can be sized as above. In addition, the other design & sizing can also be done in the same simple way to order the stabilizer (more details included in chapter 5.5 & 5.6). 5.12.3 Power Quality disturbances PQ problems can originates in, the supply system, the customer's equipments or a neighboring installation and propagate via the supply. Problems in Supply System can be Lightning strikes (Voltage transients or Failure of equipment) or Line capacitor Switching (Oscillatory transients), or Faults on 67 feeders (Voltage variations), or Asymmetrical nature of transmission lines and transformers (Voltage unbalance). Problems Originated by Customer's Equipments can be Sudden connection or disconnection of large loads which results Voltage variations, Unequal distribution ot single phase loads, Voltage unbalance, Cyclic loads, Light flicker, Power electronics loads, Harmonic distortions or High frequency noise. There are three different types of PQ disturbances; 1. Frequency events (Change of frequency outside the acceptable range) 2. Voltage events (magnitude is outside the range) 3. Waveform events (shape of the waveform is unacceptable). Frequency of the power system is established by the rotational speed of the power station generators. It is very rare that this frequency is varied significantly. 5.12.4 Voltage fluctuations Voltage fluctuations defined as repetitive or random variations in the magnitude of the supply voltage. The magnitudes of these variations do not usually exceed 10% of the nominal supply voltage. The characteristics of voltage fluctuations depend on, load type and size and the power system capacity. Voltage Swell Over Voltage1 i /'f / Voltage Sag Under Voltage Short Interruption Long Interrupti on I S lmin lhr Fig 5.18: Characteristics of voltage fluctuations The voltage waveform exhibits variations in magnitude due to the fluctuating nature or intermittent operation of connected loads. Two important parameters 68 1o voltage fluctuations are Frequency of fluctuation and Magnitude of fluctualion. Voltage fluctuations are caused when; 1. Loads draw currents having significant sudden or periodic variations. 2. The fluctuating current drawn from the supply causes additional voltage drops in the power system leading to fluctuations in the supply voltage. 3. Loads that exhibit continuous rapid variations are the most likely cause of voltage fluctuations. Examples are Arc furnaces, Arc welders, Installations with frequent motor starts (air conditioner units, fans), Motor drives with cyclic operation (mine hoists, rolling mills) and Equipment with excessive motor speed changes (wood chippers, car shredders) Voltage variations can Pe divided in to several categories; Transients, Short term variations, Long term variations, Voltage unPalance, Continuous or random fluctuations/ Flicker, Interruptions (Supply is loss completely) and Neutral to ground voltage variations (due to poor earthing practice). The Short Duration Variations is less than 1 minute and the classifications can be tabulated as follows. !Category Duration Voltage Magnitude In slant arte am Interruption <0.6 s < 0.1 pu Sag <0.6 s ' 01-0,9 pu Swell <0.6 5 1.1-1.8 pu Momentary Interruption 0.6 sto 3 s < 0.1 pu Sag 0.6 sto 3 s 0.1-0.9 pu Svrtll 0,6 s to 3 s 11-1.4 pu "temporary Interruption 3 5 to 1 min < 0.1 pu Sag 3 s to 1 min 01-0.9 pu Swell 3 s to 1 min U - U f t t j . Table 5.12: Short Duration Voltage Variation categories 69 The Long-term variation is the rms value variation at power frequency for duration more than 1 minute. The Variations are called as; 1. Under voltages - Voltage less than 90% of nominal voltage 2. Over voltages - Voltage greater than 110% of nominal voltage 3. Sustained Interruption Under voltage is decrease in rms value less than 90% of nominal value at the power frequency for duration longer than 1 minute. The Causes can be Switch on large loads, Switch off capacitor banks, Malfunction of voltage regulation equipments or Over loading circuits. Over Voltage is an increase in rms value greater than 110% of nominal value at power frequency for duration longer than 1 minute. The Causes can be Switch off large loads, Energizing capacitor banks, Incorrect tap settings of transformers or When the system is week in voltage regulation and voltage control is inadequate. Sustained Interruption exists when the supply voltage has been zero for a period of lime exceeds 1 minute. Normally these are permanent and human intervention is required to resume power. The Causes can be System fault causing "brown out" or "black out". The Wave form events result in distortion of normal sinusoidal wave shape of the voltage. There are several categories of waveform events, such as; Harmonics, Inter harmonics, Notches, Noises & Transients. The Institute of Electrical and Electronics Engineers (IEEE) has set recommended limits on both current and voltage distortion in IEEE 519-1992. Voltage distortion limits at low-voltage bus is as follows. Application class THD (voltage) Special system 3 % General system 5 % Dedicated system 10% 70 The maximum harmonic current distortion as per the IEEE 519 on Individual harmonic number (odd harmonics) is as follows. ISC/ IL <11 l l < h < 1 7 171000 15.0 7.0 6.0 2.5 20.0 Table 5.13: Maximum harmonic current distortion as per the IEEE 519 (lsc: Maximum short-circuits current at the Point of Common Coupling (PCC), II: Maximum demand load current (fundamental) at the PCC). Voltage fluctuations in power systems also cause a number of harmful technical effects resulting in disruption to production processes with substantial costs. Light Flicker results due to voltage fluctuations. In the Electric machines, Change in torque and In the worst case, excessive vibration, reducing mechanical strength and shortening the motor service life, will results due to voltage fluctuations. In the Static rectifiers, generation of non-characteristic harmonics and inter-harmonics can be seen. The sensitivity to voltage fluctuations is a function of the frequency and it is also dependent on the voltage level of the lighting. Voltage sags on the supply system have a significant retained voltage, So that energy is still available. For these equipments, no energy storage mechanism is required and relies on generating full voltage from the energy still available at reduced voltage during the dip and they are known as "Automatic Voltage Stabilizes". The main types of Automatic Voltage Stabilizers available are Electro- mechanical, Electronic step regulators, Electronic voltage stabilizer (EVS) and Ferro-resonant or constant voltage transformer (CVT). The Voltage Sag is mainly affect to the telecom equipment operations and also effects to Power Electronics & Process control Equipments and, Loss of production, Damage product & Damage equipments can be seen. There are two sources of voltage sags, External on the utility's lines up to the facility or Internal within the facility. Utilities continuously strive to provide the most 71 reliable and consistent electric power possible. In most cases, the majority of sags are generated inside a facility. 5.12.5 Managing PQ Problems Control of PQ problems involves cooperation between network operator, customer and equipment manufacturer. Most PQ problems can be solved within the plant itself. Careful identification of the source of PQ problem is essential. General Guide to Manage PQ Problems can be listed as follows. 1. Identify the weaknesses in the power supply (Monitoring the supply), 2. Identify the critical components and their susceptibility to power quality events, 3. Specify all new critical equipments to withstand worse case supply conditions, 4. Seek assurance from equipment manufactures that the equipment meets PQ specifications, 5. Ensure that the equipment purchased dose not cause further degradation of PQ. The effects of voltage fluctuations depend on their amplitude, which influenced by the characteristics of the power system, and Rate of their occurrence, which determined by the technological process, i.e. type of load and character of its operation. Usually, mitigation measures are targeted at actions focused on limiting the amplitude of the voltage fluctuations. The Plant Level Options can be characterized as follows. In the Arc furnace, it is possible to incorporate a series reactor (or variable saturation), proper functioning of the electrode control system, segregation and preliminary heating of charge, etc. In the Welding plant, it is possible to supply the plant from a dedicated transformer, connecting single-phase welders to the three-phase network for balanced load distribution between phases, and also by connecting single phase welding machines to different phases from those 72 powering lighting equipment, etc. In the Adjustable speed drives, it is possible to use of soft-start devices. The Utility Level Options can be characterized as follows. Increasing the short circuit power (with respect to the load power) at the point of coupling to which a fluctuating load is connected. It is possible to connect the load at a higher nominal voltage level or supplying this category of loads from dedicated lines or separating supplies to fluctuating loads from steady loads, or increasing the rated power of the transformer supplying the fluctuating load, or installing series capacitors. Reducing the changes of reactive power in the supply system by; installing dynamic compensators/stabilizers. Negotiate with the supply company for a lower impedance connection, Reduce the number of line Faults by Use UG cables instead of OH lines & Wave leaves clearing and Reduce the fault clearing time are some of the System Improvements. 5.12.6 Power Quality Standards International Standards Groups mainly includes the IEC, EN, ANSI, IEEE, NEMA standards and include standards for PQ. 1. International Electro technical Commission (IEC) Industry group that writes and distributes standards for electrical products and components in general. 2. European Norm (EN) or European Standard, which carries with it the obligation to be implemented at national level and having priority over any conflicting national standard CIGRE (SC 36). 3. American National Standard Institute (ANSI) ANSI facilitates the development of American National Standards (ANS) by accrediting the procedures of standards developing organizations. 4. Institute of Electrical and Electronics Engineers (IEEE) , The Institute of Electrical and Electronics Engineers Standards Association (IEEE-SA) is the leading developer of global industry standards in a broad-range of industries, including the Power and Energy. 73 5. National Electrical Manufacturers Association (NEMA) , National Institutes of Science and Technology (NIST), National Electrical Code, NFPA 70, National Fire Protection Association} NFPA), Underwriters Laboratories (UL). The following IEEE standards include the standards relevant for the PQ. IEEE 1159 (Monitoring Electric Power Quality), IEEE 1159.1 (Guide For Recorder and Data Acquisition Requirements), IEEE 1159.2 (Power Quality Event Characterization), IEEE 1159.3 (Data File Format for Power Quality Data Interchange), IEEE 1564 (Voltage Sag Indices), IEEE 1346 (Power System Compatibility with Process Equipment), IEEE 1100 (Power and Grounding Electronic Equipment, IEEE 1433 (Power Quality Definitions), IEEE 1453 (Voltage flicker), IEEE 519 (Harmonic Control in Electrical Power Systems), IEEE 519A (Guide for Applying Harmonic Limits on Power Systems), IEEE 446 (Emergency and standby power), IEEE 1409 (Distribution Custom Power), IEEE 1547 (Distributed Resources and Electric Power Systems Interconnection), etc As per European Standard, EN 50160, the purpose of the standard is to direct in the proper monitoring and data interpretation of electromagnetic phenomena that cause power quality problems. The categories and their descriptions are important in order to be able to classify measurement results. Supply voltage phenomenon Acceptable limits Measurement Interval Monitoring Period Acceptance t'ei rentage Gnd frequency JZ August 08 September 08 October 08 November 08 Fig 6.2: Graphical representation of Customer Complains in last 4 months The above graph shown a significant reduction of customer complains especially on Coverage & noise issues which are related with power quality of the base station served to the respective customer. Hence, the reduction of complains will indicate the improvement of customer satisfaction & quality of the service in the month of November 2008. The available records of the total customer base can not be filtered by each site or by network patterns. In addition, those records will vary on many other factors also. Hence, the above reduction may not justifiable to relate directly to the scope at this stage but more clear result can be obtained after completion of 124 sites in the 2nd stage. However, as this project already could reduce the downtime of 19 of backbone sites out of 40 in the network, we can believe on a justifiable relation with the above reduction of customer complains as improvements of the network up time. 80 6.4 Reduction of the Operational Overhead The operation overhead of the Maintenance Department (Lanka Bell Limited) can be categorized in to the followings areas and the expenses will not allow to increase than the budgeted values, except in special cases with higher management approvals. The overhead categories with the budgeted values for the financial year 2008 can be tabulated as follows. OPEX category Budgeted value (Rs. In Million) Electricity 450 M Spares & Consumables 42 M Diesel for generator operation 35 M Transport 3.8 M Staff expenses (Meal, OT, on call, OPA, Logins) 1.8 M Plant, equipment & tool repairs & replacements 1.6 M Service Contracts 7.1 M Equipment Rental 0.8 M Office expenses (mobile, stationery, training, etc) 0.4 M Miscellaneous 0.2 M Table 6.6: Summary of the budgeted OPEX categories for maintenance The actual expenses under the above operational overhead can be obtained from the following reports. 1. "Operation Overhead Report" of Maintenance Department, 2. "BTS Electricity Cost Report" of Maintenance Department, 3. "Maintenance Spare Part expense Report" of Warehouse, 4. "Generator Diesel Expenses Report" of Transport Department 5. "Preventive Maintenance expense Report" of Maintenance Department 6. "Cluster OPA Expense Report" of Clusters The Operational expenses related to base stations maintenance (except of main administration & switching centers in Colombo) for last 4 months can be tabulated as follows. 81 OPEX Category Actual Expenses (Rs. ,000) August September October November Electricity 12,635 13,358 12,226 12,287 Spares & Consumables 720 635 810 705 Diesel for generator 4,360 3,250 4,128 2,910 operation Transport 316 425 367 298 Staff expenses (Meal, over time, on call, OPA, Logins) 156 178 127 95 Plant, equipment & tool repairs & replacements 33 47 28 32 Service Contracts 345 352 362 325 Equipment Rental 12 15 14 6 Office expenses (mobile, 52 58 62 48 stationery, training, etc) Miscellaneous 8 9 7 8 Table 6.7: Summary of the actual OPEX in last 4 months The Graphical representation of the main OPEX items is as follows. Fig 6.3: Graphical representation of main actual OPEX in last 4 months 82 The above graph shown a significant reduction of OPEX especially on Electricity, Spare, Diesel and Transport which are related with power quality of the base station sites. As the initial 19 sites selected are highest Generator running sites due to huge voltage drops, the above OPEX reductions are directly outcomes of this project and further reduction is possible after completion of 124 sites in the 2nd stage before May 2009. As a summary, it is already shown that, the research project implemented at 19 main backbone sites gave significant benefits in terms of OPEX & CAPEX reductions to the company. This is very important as, the selected 19 sites in stage 1 are very critical sites having many interconnections of the network and reduction of outages is very important and the uptime of those sites are considerable revenue source to the company. It is also important to note that, the data shown above are having only just a month of data after implementing this project. Hence, the cyclic variations and any other factors continuing from past 3 months can affect to the variations of the figures in the 4th month. Therefore, any benefit/ cost reductions in the month of November 2008 can not justifiable to relate directly as benefit of this project at this stage as data available is not enough for such a decision, as only this month data in hand. Hence, we can get more accurate picture on the implementation progress after completing the stage 2 of this project (124 sites, next 87% of the scope) and our target is to complete before May 2009, assuming the required funding possible to be acquired from the company. We must thank to the Management of Lanka Bell Ltd as they already grant over Rs. 1,600,00.00 funding for the stage 1 of this implementation after accepting the possible benefits of this project which produce more revenue with in a very short payback period. 83 Chapter 7 FINANCIAL FESIBILITY ANALYSIS 7.1 Overview The financial feasibility of this project will discuss on the capital investment for this voltage correction system including the associate modifications at each sites categorized under RBS Models, over the savings on Generator operation cost reductions and savings on uninterrupted customer service from the respective base station sites, in case by case basic. As the outages of such sites are very critical & major revenue loss to the company, expenditures to keep the extended up time are justifiable and having short pay back period. The cost considerations can be listed as follows. Expenditures 1. Cost for the initial testing & information surveys. 2. Cost for the modifications & additions to the power related equipments. 3. Cost for the purchase of voltage stabilizers which were locally designed & fabricated, as per the customer specifications & requirements. 4. Cost for further modifications, improvements & advancements of the systems. Savings 1. Reduction of Generator operation cost. 2. Reduction of revenue losses due to customer service outages. 3. Reduction of expenditures for repairs of equipment damaged due to low voltage. 4. Reduction of energy losses on low voltage operation and savings due to improved efficiency of the system and associated operations. The detailed calculations of the above cost considerations are discussed from next page onward with the assumptions taken. 84 7.2 Cost Calculation for Generator Operation at Telecom Base Station 7.2.1 Diesel Generator as Back up Power Source Statistics {Assumptions for Cost calculation) J Rate Unit General Details Capacity of the Generator 12 5 KVA Purchased Price (Capital) 9 600 USS Distance to the site from Colombo 150 Kms Distance to the site from Cluster 40 Kms Commercial Power Availability (Yes/ No) Yes Operational Details BTS Loading (Power) 60 % of full load Generator Operating Hours per Day (Avg.) 5 Hrs/ Day @ CEB Peak Number of Preventive Maintenance 4 Jobs/ Year Recommended Lifetime of the Generator 16.000 Hrs Residual Values of Generator 10 % of capital Generator Fuel Consumption 3 2 Liters/ Hr @ 80% Load Generator Output Power (Amp 3Ph) 18 Amp/ Phase Generator Re-fuel Level (Diesel Top-up) 45 Liters Financial Details Site Rental charges 15,000 Rs/ Month Transport cost 25.00 Rs / Km Portal Charges 500 Rs/ Can Professional expenses 5,000 Rs/ Visit Salary of Diesel Technician 450 Rs/ Day Salary of Generator Technician 15,000 Rs/ Month Cost for OPA (Foods & Login) 600 Rs/ Day Price of Diesel 120 00 Rs/ Liter Price of Consumables (Lube Oil, Oil/ Fuel Filters, Battery Water, etc) 4,240 Rs/ Sen/ice Mini O/erhaul cost (Material + Labor) 350,000 Rs/ Job Major Overhaul cost (Material + Labor) 650,000 Rs/ Job Selling Markup of the Gen power 30 % of actual 85 Cost Calculation {Generator Operation) Qty Unit Cosf (Rs.) Capital & Initial Expenditures Generator Depreciation 1 Life Each Month 8,910 00 Site Rental charges (Plinth space) 005 Rental % Each Month 750.00 Installation & Commissioning Transport (Up & Down) 300 Kms Initial 7,500 00 Labor (Technician) 2 Man Days Initial 1 200 00 Professional expenses 1 Visits Initial 5,000.00 Foods & Login 2 Man Days Initial 1 200.00 Periodical Service Expenditures Preventive Service Consumables 4 Service Each Year 16,960 00 Transport (Up & Down) 80 Kms Each Year 2 000 00 Labor (Technician) 2 Man Days Each Year 1,200 00 Foods & Login 2 Man Days Each Year 1,200.00 Overhauling Cost Mini Overhaul at each 5,000 hrs 2 Life Each Year 383 56 Diesel Expenditures Diesel 2 4 Liters Each Hour 288 00 Transport (Up & Down) 80 Kms Each Visit 2,000 00 Portal Charges 2 Cans (20L) Each Visit 1,125 00 Labor (Diesel Tech.) 0.25 Man Days Each Visit 112.50 Total Cost on the Gen Operation Fixed Cost (Per Month) 46.145 Rs/ Month Vanable Cost (Per Hour ort BTS load) 288 Rs/ Gen Hr Final Value for the Operator (per Month) 89,345 Rs/ Month plus VAT (Fixed cost + Unit consumed x Rate) 86 7.2.2 Diesel Generator as Main Power Source Rate Unit General Details Capacity of the Generator 12.5 KVA Purchased Price (Capital) 9,600 US$ Distance to the site from Colombo 150 Kms Distance to the site from Cluster 40 Kms Commercial Power Availability (Yes/ No) No Operational Details BTS Loading (Power) 60 % of full load Generator Operating Hours per Day (Avg. ) 24 Hrs/ Day @ CEB Peak Number of Preventive Maintenance 4 Jobs/ Year Recommended Lifetime of the Generator 16.000 Hrs Residual Values of Generator 10 % of capital Liters/ Hr @ 80% Load Generator Fuel Consumption 3 2 Generator Output Power (Amp 3Ph) 18 Amp/ Phase Generator Re-fuel Level (Diesel Top-up) 45 Liters Financial Details Site Rental charges 15.000 Rs/ Month Transport cost 25 00 Rs/ Km Portal Charges 500 Rs/ Can Professional expenses 5.000 Rs/ Visit Salary of Diesel Technician 450 Rs/ Day Salary of Generator Technician 15,000 Rs/ Month Cost for OPA (Foods & Login) 600 Rs/ Day Price of Diesel 120.00 Rs/ Liter Price of Consumables (Lube Oil. Oil/ Fuel Filters Batten/Water, etc) 4,240 Rs/ Service Mini Overhaul cost (Material + Labor) 350,000 Rs/ Job Major Overhaul cost (Material + Labor) 650,000 Rs/ Job Selling Markup of the Gen power 30 % of actual Cost Calculation (Generator Operation) Qix Unit Cost (Rs.l Capital & Initial Expenditures Generator Depreciation 1 Life Each Month 42.768.00 Site Rental charges (Plinth space) 0.05 Rental % Each Month 750.00 Installation & Commissioning Transport (Up & Down) 300 Kms Initial 7,500.00 Labor (Technician) 2 Man Days Initial 1,200.00 Professional expenses 1 Visits Initial 5,000 00 Foods & Login 2 Man Days Initial 1.200.00 Periodical Service Expenditures Preventive Service Consumables 4 Service Each Year 16,960.00 Transport (Up & Down) 80 Kms Each Year 2,000.00 Labor (Technician) 2 Man Days Each Year 1 200 00 Foods & Login 2 Man Days Each Year 1.200 00 Overhauling Cost Mini Overhaul at each 5,000 hrs 2 Life Each Year 79 91 Diesel Expenditures Diesel 2.4 Liters Each Hour 288.00 Transport (Up & Down) 80 Kms Each Visit 2.000,00 Portal Charges 2 Cans (20L) Each Visit 1.125.00 Labor (Diesel Tech.) 0 25 Man Days Each Visit 112.50 Total Cost on the Gen Operation Fixed Cost (Per Month) 211,735 Rs/ Month Van able Cost (Per Hour on BTS load) 288 Rs/ Gen Hr Final Value for the Operator (per Month) 419,095 Rs/ Month plus VAT (Fixed cost + Unit consumed x Rate) 7.2.3 Summary of the Generator operational cost vs. running hours The above is for the operation cost of Generator as backup power during normal light peak voltage reduction period (as per CEB load curve, the highest loading observed and the power will be dropped during 6 - 8am and 6 - 9pm with the light loading) and as full 24hr running at none CEB power available sites. The intermediate values are calculated and tabulated as follows. Gen running hours (hrs) Operational Fixed cost (Rs) Operational variable cost (Rs) Total operational cost per Month (Rs) 1 11,406 8,640 20,046 2 20,043 17,280 37,323 3 28,733 25,920 54,653 4 37,436 34,560 71,996 5 46,145 43,200 89,345 6 54,856 51,840 106,696 7 63,569 60,480 124,049 8 72,283 69,120 141,403 9 80,997 77,760 158,757 10 89,712 86,400 176,112 11 98,427 95,040 193,467 12 107,143 103,680 210,823 13 115,858 112,320 228,178 14 124,574 120,960 245,534 15 133,290 129,600 262,890 16 142,006 138,240 280,246 17 150,722 146,880 297,602 18 159,438 155,520 314,958 19 168,154 164,160 332,314 20 176,870 172,800 349,670 21 185,586 181,440 367,026 22 194,303 190,080 384,383 23 203,019 198,720 401,739 24 211,735 207,360 419,095 Table 7.1: Generator operation cost vs. running hours at radio base station site. 7.3 Analysis of Traffic loading on standard Telecom Base Station site The calculation of the revenue loss during the base station downtime can be calculated for different RBS Models and the areas considered can be described below. 89 The customer loading on the base station site will depend on the time period of the day and some of the collected BTS Traffic curves (specially considering the 19 under voltage sites) can be shown as follows. The Y axis is Traffic in "Erlang" which is the measuring unit on customers loading (Traffic) per line average in one hour period. It can roughly assume number of call hours handled during the given one minutes period (1 Erlang = 60 min of usage). 10/1/2008 10/2/2008 10/3/2008 10/4/2008 10/5/2008 10/6/2008 Fig 7.1: Traffic curve (in Erlang) of Badalkumbura RBS site for one week per iod 10 15 20 -10/1/2008 -10/2/2008 -10/3/2008 -10/4/2008 -10/5/2008 Fig 7.2: Traffic curve (in Erlang) of Hatharal iyadda RBS site for one week period However, most of the curves are in same shape and this is mainly due to the call charges (time of day tariff) in time slot basis. In addition, average set up time (ringing time before call connects) is 30% of the total call in Erlang curve and hence only 70% will applicable for the effective revenue calculations. The Average holding time (call time) is 1.8 Minutes (33 calls per hour) and can be used for the calculations. 7.4 Analysis of Tariff packages applicable for fhe customers In order to calculate the revenue earned, the common few tariffs can be considered as flows, which covers post paid, pre paid and IDD customers. 90 7.4.1 Tariff Charges on post paid customers Lanka Bell to Lanka Bell Peak Standard Economy * Rs / Per Minute * Rs / Per Minute * Rs / Per Minute Local 1.50 0.75 0.10 National 3.75 1.60 0.35 Lanka Bell to Other Operator Peak Standard Economy * Rs / Per Minute * Rs / Per Minute * Rs / Per Minute Local 1.75 1.00 0.20 National 4.40 2.00 0.60 Table 7.2: Tariff Charges on post pa id customers. Monthly Rental Rs.320.00, Start up fee Rs.2.95 per call and Incoming totally free. Peak - Monday to Saturday 7.00 am to 6.00 pm. Standard - Monday to Saturday 6.00 pm to 9.00 pm. Off Peak - Monday to Saturday 9.00 pm to 7.00 am. Sundays & Public Holidays 7.4.2 Tariff Charges on Pre paid customers Available In denomination of Rs. 5000, Rs. 2,500, Rs.1000, Rs.500 and Rs.300, Bell Tell also offers affordable call rates and per minute charges as follows. Lanka Bell to Lanka Bell Standard Economy * Rs / Per Minute * Rs / Per Minute Local 2.90 1.90 National 3.90 2.90 Lanka Bell to Other Operators Standard Economy * Rs / Per Minute * Rs / Per Minute Local 2.90 1.90 National 3.90 2.90 Table 7.3: Tariff Charges on pre pa id customers. 91 7.4.3 Tariff Charges on IDD customers Country To Fixed Lines To Mobiles AUSTRALIA 8 20 BANGLADESH 8 1 1 C A N A D A 8 8 CHINA 8 1 1 FRANCE 8 20 H O N G KONG 8 11 INDIA 12 25 INDONESIA 8 20 ITALY 8 20 JAPAN 8 20 KOREA SOUTH 8 11 KUWAIT 10 25 MALDIVE IS 25 30 NEPAL 25 35 NEW ZEALAND 8 20 QATAR 25 35 SINGAPORE 8 1 1 SOUTH AFRICA 8 20 TAIWAN 8 1 1 THAILAND 8 1 1 UNITED K INGDOM 8 20 USA 8 8 Average 11 18 Table 7.4: Tariff Charges on IDD customers. 7.4.4 Summary of Revenue calculation on call charges for a period of 24hrs Generally assuming the calls handled by the RBS in the following Tariff basis, the revenue can be averagely tabulated for the hour basis from the above data collected. Percentage of Post paid customers (local calls only) - 70 % Percentage of pre paid customers (local calls only) - 27 % Percentage of IDD customers (to fixed lines) - 3 % The revenue on each time slot can be calculated with the above assumptions and this will reflect the incoming from standard base station site. 92 Example: Unit call charge at 20.00 = [(33 x 2.95)+(0.2x 0.7+2.9x 0.27+1 lx 0.03)x 60]/60 = Rs. 2.88/ min Revenue = Rs. 2.88/ min x 35 Erlang x 60 x 70% = Rs. 4,227.00 The same can be calculated for the other time bands and tabulated as follows. Time slot of Day Customer Loading Average post paid charge (Rs/min) Average pre paid charge (Rs/min) Average IDD charge (Rs/min) Unit call charge (Rs/min) Revenue (Rs/hour) 00.00-01.00 1 1 2.9 11 3.44 144 01.00-04.00 2 1 2.9 11 3.44 289 04.00-08.00 20 1.75 2.9 11 3.96 3,327 08.00-12.00 10 1.75 2.9 11 3.96 1,663 12.00-16.00 15 1.75 2.9 11 3.96 2,495 16.00-20.00 35 0.2 2.9 11 2.88 4,227 20.00-24.00 3 1 2.9 11 3.44 433 Table 7.5: Revenue calculat ion on call charges for a period of 24 hours 7.5 Revenue saving per day on each RBS Model The voltage stabilizing unit will help to maintain the customer operation without any outage and hence the saving of the revenue in the stabilizer operation period can be considered as the outcome of this project and listed as follows, for each RBS Model. RBS Model Stabilizer Period Revenue saving per day 0 None No Interruption 1 6 - 8am & 6 - 9pm (5 hrs/ day) Rs. 3,327 x 2 hrs + Rs. 4,227 x 2hrs + Rs. 433 x 1 hrs = Rs 15,541 per day 2(a) 5 - 10am & 4 - 9pm (10 hrs/ day) Rs. 3,327 x 3 hrs + Rs. 1,663 x 2 hrs + Rs. 4,227 x 4hrs + Rs. 433 x 1 hrs = Rs 30,648 per day 2(b) 5 - 10am & 4 - 9 pm (10 hrs/ day) Rs. 3,327 x 3 hrs + Rs. 1,663 x 2 hrs + Rs. 4,227 x 4hrs + Rs. 433 x 1 hrs = Rs 30,648 per day 3 Full day Rs. 144 x 1 hrs + Rs. 289 x 3 hrs + Rs. 3,327 x 4 hrs + Rs. 1,663 x 4 hrs + Rs. 2,495 x 4 hrs + Rs. 4,227 x 4 hrs + Rs. 433 x 4hrs = Rs 49,591 per day 4 None RsO Table 7.6: Revenue saving per day calculat ion on each RBS Model 93 The expenses on the stabilizers and panel modifications can follows. The total cost for the systems is Rs. 1,542,000 and other assumed less than Rs. 40,000. be summarized overheads can as be CASE NO CLUSTERS RBS NAME GEN TYPE ATS TYPE POWER SUPPLY UNDER VOLTAGE RANGE GEN RUN TIME SOLUTION POSSIBILITY SOLUTION FOR THE UNDER VOLTAGE HEW ATS MODIFY PANEL 3 KVA AVS FOR AC 8 KVA AVS FOR INPUT Kandy 1 1 Haiharaliyadde 1 Cummins Cummins 3 OA, 1ph 130-140 Continuously YES 1 2 2 Dambulla 2 Cummins Cummins 30A, 1ph 175-190 4PM-10PM YES 1 3 Wahakotte Pendinq supply by CEB & already requested NO 4 Karaqahathanna No CEB Gen 24 hrs Running & Transformer needed NO 5 Madamahanuwara No CEB Gen 24 hrs Runninq & Transformer needed NO 6 Galaqedara No CEB. Gen 24 hrs Runninq & Transformer needed NO 7 Katuqastota No CEB Gen 24 hrs Runninq & Transformer needed NO 3 A/ikumbura No CEB Gen 24 hrs Runninq & Transformer needed NO 9 Ka-Afdupelella No CEB Gen 24 hrs Runninq & Transformer needed NO 10 Nildandahinna No CEB. Gen 24 hrs Runninq & Transformer needed NO 11 Rikillaqaskada No CEB. Gen 24 hrs Runninq & Transformer needed NO 12 Dodanqaslanda No CEB Gen 24 hrs Runninq & Transformer needed NO Rathnapura 1 13 Kunjwita 3 FG Wilson ATI63 30A, 1ph 140-160 24Hr CEB YES 1 2 1 14 Parakaduwa 4 Temast Hayles 30A 1pb 160-170 6PM-11PM YES 1 15 Neuqala 5 Temast Hayles 30A. 3ph 160-180 5PM-11PM YES 1 2 16 Niwithiqala No CEB Gen 24 hrs Runninq & Transformer needed NO 17 Inqiriya Pendinq supply by CEB & already requested NO 18 Avissawella Pendinq supply by CEB & already requested NO 19 Endana Pendinq supply by CEB & already requested. NO 20 Thalduwa Pendinq supply by CEB & already requested. NO 21 Hettimulla No CEB, Gen 24 hrs Runninq & Transformer needed MO 22 Ratnaoura No CEB. Gen 24 hrs Runninq & Transformer needed NO 23 Kirielta Pendinq supply by CEB & already requested NO Monaragala 2 24 Mahaoya S FG Wilson nro 30A. 1ph 150-155 Continuously YES 1 2 25 Batticaloa 7 FG Wilson TI70 30A. 1ph 160-165 Continuously YES 1 2 26 Badalkumbura 8 FG Wilson TI70 30A, 1ph 170-175 Continuously YES 1 27 Meda qa ma 9 FG Wilson TI70 30A, 3ah 170-180 Continuously YES 1 2 28 Weilawaya 10 Temast Hayles 30A 1ph 170-175 Continuously YES 1 29 Ridipana No CEB. Gen 24 hrs Runninq & Transformer needed NO Matara 1 30 Kananke 11 FG Wilson T170 30A, 1ph 150-155 Continuously YES 1 2 31 Riiaqala 12 FG Wilson T170 30 A 1ph 160-170 4PM-10PM YES 1 2 32 Gandara 13 FG Wilson TI70 30A, 1ph 160-170 4PM-10PM YES 1 1 33 Henaqqeqoda Pendinq supply by CEB & already requested NO 34 Gatebarukanda Pendinq supply by CEB & already requested NO 35 Mapalaqama No CEB. Gen 24 hrs Runninq Transformer needed NO 36 Morawaka Pendinq supply by CEB & already requested. NO 37 Kamburupitiya Pendinq supply by CEB & already requested. MO 38 Yakkalaroulla Pendinq supply by CEB & already requested NO Anuradapura 1 39 Minneriya 14 FG Wilson T170 30 A 1pti 165-180 Continuously YES 1 2 40 Galenbindunuwea 15 FG Wilson T17Q 30A 1ph 170-180 5PM-10PM YES 1 1 41 Nochchiyaqama 16 Hayles Hayles 30A 1ph 170-180 6PM-10PM YES 1 1 42 Jayanthipura Pendinq supply by CEB & already requested NO Kurunegala 1 43 Riaeeqama I 7 FG Wilson 1170 30A, 1ph 160-195 Continuously YES 1 2 1 44 Poipithigama 18 FG Wilson AT163 30A, 1ph 160-170 Continuously YES 1 1 45 Maspotha 19 FG Wilson T170 30A, 1ph 170-180 5PM-10PM YES 1 1 46 Karuwalasaswewa Pending supply by CEB & already requested NO Standby Units 2 3 1 Qty each type 6 11 30 12 Unit cost 60 000 15 000 19.500 36 000 Total Cost 360 000 165.000 585.000 432 000 1,542,000 Table 7.7: Details of RBS which having highest Gen. running & possibility of the solutions 94 The summary of cost components are as follows. Total cost for the voltage stabilizing systems for 19 sites = Rs. 1,582,000 Total revenue saving per month at 19 sites by extending the up time with stabilizers can be summarized for each RBS Model as follows. RBS Model Number of sites Revenue saving by extended Up time Generator running cost Total Saving per month of all sites 0 124 Not yet considered Few Considerable 1 4 Rs 466,230 Rs. 89,345 Rs. 1,507,540 2(a) 6 Rs 919,440 Rs. 176,112 Rs. 4,459,968 2(b) 4 Rs 919,440 Rs. 176,112 Rs. 2,973,312 3 4 Rs 1,487,730 Rs. 419,095 Rs. 4,274,540 4 27 Not yet considered Rs. 419,095 N/A Table 7.8: Total saving per day calculation on each RBS Model The total saving is around Rs. 13,215,360 per month and capital cost is only Rs. 1,582,000. Hence, without any further justification, this project is financially viable and possible to proceed. 95 Chapter 8 CONCLUSION The main objective of this project was to suggest the most economical way of running the remotely located low voltage sites by reducing the customer service interruptions while minimizing the OPEX on day to day operations. With the recorded data after one month test running period, remarkable results could be obtained and also proved that the projects is financially viable. This development will help the company to face the challenging marketplace to sustain with the competitive Tariff reductions and demanding advancement of services to customers with minimum investment. Not like in other industry, the telecom customer is having the freedom to select any other service provider by their own decision without facing any monopoly or other influences. This automatically creates the industry to reduce their OPEX & CAPEX continually to sustain with the market share. The CAPEX is always increasing and the reduction possibility exists only with OPEX. This project could save the major portion of the OPEX by keeping other facilities in better condition and this was a remarkable achievement. The test observations proved that the system develop for the automatic voltage regulation at remote telecom sites can operate under extreme climate, environmental & power abnormality conditions to regulate & maintain reliable & accurate sinusoidal voltage profile to the sensitive telecommunication equipments, without any single failure to the systems. In addition, the development of the unit is capable of meeting the protection requirements from various environmental/ power abnormalities and kept the sites free from any outside effects. We believe that, the outcomes of this research will be a remarkable development in the telecom industry. We also supposed to share this knowledge with all the interesting parties to extend the benefits not only to the telecom service providers, but also to the customers by means of further reduction in tariffs. 96 REFERENCESS [1] Robin Koffler, Jason Yates, "The Power Protection Guide", Technical Guide of Riello UPS, vol. 1, pp 15-33, 2007. [2] Web Site: http://www.ashleyedison.com, Ashley-Edison International Limited. [3] J.W.D.Somasundara, N.N.K.P.Withanage, "Problems and Prospects of Telecommunications Services in the Ratnapura District", Research Paper published in TRCSL website, pp 235-238, 2006. [4] H.S.C Perera, "Services Quality and Telecommunications Services in the Southern Province in Sri Lanka", Research Paper published in TRCSL website, pp 106-139, 2004. [5] Flanagan, William, "Handbook of Transformer Design and Applications", McGraw-Hill, pp 22-65, 1993. [6] V.N. Mittle, A. 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Andreas, "Energy Efficient Electric Motors - Selection & Applications", 2nd edition, Marcel Dekker Inc, pp 65-258, 1992. [15] Nandike Pathirage, "Solving the Under Voltage problem in Sri Lanka National grid", Thesis for MSc at University of Moratuwa, 2001. [16] P.C. Devasurendra, "Investigation of Voltage Profile in Low voltage Distribution Network", Thesis for MSc at University of Moratuwa, 2006. [17] Web Site: http://www.success.com.my, Success Electronic & Transformer manufacturer Limited Homepage. [18] Donald G. Fink and H. Wayne Beaty, "Standard Handbook for Electrical Engineers", Eleventh Edition, McGraw-Hill, New York, 1978. [19] Bandula S. Tilakasena, K.A. Noel Priyantha, "End-user characteristics of the electricity demand in Sri Lanka", Research paper published in CEB website, 2001. [20] M.T.K. De Silva, "Design of Power Electronic Inverter for Active power reduction in an unbalance 3 phase system", Thesis for MSc at University of Moratuwa, pp 33-33, 2004. [21] G.Weerasekara, "Voltage Sag mitigation using Dynamic voltage restore with multi-feedback control", Thesis for MSc at University of Moratuwa, pp 33-33, 2005. [22] H.C.S. Hettigoda, "Hardware Implementation of a Power system stabilizer", Thesis for MSc at University of Moratuwa, 2002. [23] Website: http://www.wapa.gov, Western Area Power Administration, an agency of U.S. Department of energy website. [24] Professor V.J. Gosbell, "Voltage fluctuations in the electric supply system", Technical Note for Integral Energy Power Quality Centre, University of Wollongong, 2003. 98 R « R 10 12 H I H 2 H 3 6A/VSE I 0/ £ C LEG EN D - M O ULD ED CASE CIRCUIT BRCAKL V -R E S ID U A L C U R R E N T ^ C IR C U IT B R E A K E R J - M IN IA TU R E * C IR C U IT B R E A K E R 4 1- - PR O TE C TIO N FU SE g ) - INDICATO R LAM P * N O T E :- A L L C O N TR O L C A B LE A R E 1.5sqm m FLE X IB LE C A B LE D ciaurncM DESIGNED ST CMECXZD BY A A M lO V tD »T L A N K A B E L L (P V T )L T D , LEVEL 6, EA ST LO W ER BLO CK 1, W O R LD TR AD E C EN TR E,EC H ELO N SQ AAE, C O LO M B O 1 ,SR1 LArtKA. L A N K A B E L L (P V T )L T D , N O : 11, M A H A W ELA R O A D , D fM A T A G O O A . C O LO M B O 9,SR I LAN KA. P A N E L ID : R B S P O W E R P A N E L S D R A W IN G T IT L E : S IN G L E L IN E L A Y O U T L A N K A B E L L L T D T E C H N I C A L O P E R A T I O N S D E P A R T M E N T D W G . STATU S R .I.J. 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