Investigating the effects of electromagnetic fields due to high voltage transmission lines on detonator firing circuits

Abstract

High voltage A.C. transmission is the common mode adopted in transmitting bulk electrical power from one station to the other all over the world. Associated with these overhead transmission lines are the electric and magnetic fields emanating from these which could have a coupling influence on devices in its proximity. Detonator is one such electro explosive device (EED) that is susceptible to electromagnetic coupling when placed in proximity to the transmission lines which in turn could cause inadvertent misfires. This report focuses on the computational modeling of electric and magnetic fields around overhead high voltage transmission lines at various voltage levels and line configurations starting from fundamental electromagnetic principles and the verification of those models by field measurements. MATLAB software was used in modeling the field profiles and the model is capable of accommodating any configuration with any number combination of conductors. The overhead transmission line parameters used in this report are from the present line configurations in practice in Sri Lanka. The measured values of electric and magnetic fields are compared with the modeled values for the verification of models. The possibility of shielding these extra low frequency electromagnetic fields are also discussed briefly. Electrical detonator is one type of Electro Explosive Devices (EEDs) that is used to initiate blast sequences. the susceptibility of these devices to the electric and magnetic fields emanating from nearby high voltage transmission lines are comprehensively examined under scenarios of nominal rated loads, infrequent high loads, emergency short-time loads, faults, lightning and switching surges. Investigating the impacts of field couplings and possible unintentional misfires under different scenarios, safe distance levels for operation of detonators in the proximity of transmission lines are proposed for different voltages and line configurations.