An improved DC load flow technique for reliability studies of power systems

Abstract

One of the major problems facing the power . system engineer in a developing country today is the inability of the computers available in his country to execute a majority of the computer programs due to the small memory capacities of these computers. Usually the amount of storage required by the conventional programs is too large. The high cost of computer time is another problem. Programs which require long time for execution gives rise to excessive cost. Almost all methods available in the evaluation of reliability of power systems, for example, require load flow analysis. The bulk of the computation time is utilized in load flow analysis of each outage condition*. Accurate load flow techniques such as the Gauss-Seidal and Newton-Raphson methods are computationally expensive. Approximate load flow techniques such as the dc load flow are very fast but provide only estimates of line power flowsl They give no estimate of bus voltages which are essential in calculating the reliability indices of individual system buses. 2 3 The problem has been solved by Karunaratne and Karunaratne et al by presenting a dc load flow technique which is capable of simulating both the real power flow and the reactive power flow on a dc network analyser; and is therefore able to provide estimates of both line power flows and bus voltages. However, the problem of this technique is that it cannot be used directly on a digital computer. This problem has been solved in this dissertation by modifying and improving the technique in order to extend its application to a digital computer. The resulting technique which is referred - 2 - to as the Improved D.C. Load Flow (IDCLF) in this dissertation is then used in the evaluation of the reliability of the two power systems. A brief background and historical development of reliability studies of power systems is given in Chapter 2. The reasons which led to the change in methods of evaluation from qualitative to quantitative are also outlined. Chapter 3 gives a description of qualitative methods which were used in early days. In Chapter 4 the techniques which are used in load flow analysis for modern power systems are described. In section 4.1 the popular Fast Decoupled Load Flow (FDLF) technique has been described because it is the most efficient ac load flow technique available. In section 4.2 the dc load flow technique presented 2 3 by Karunaratne and Karunaratne et al which is used on a dc network analyser has been described. A. step by step description of how the technique is modified and improved in order to extend its application to