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An analysis of switching overvoltages in the EGAT 500 kV transmission system

The level of transient overvoltage has a strong effect on power system reliability. It has already been known that switching overvoltages are the most important criteria which the design of insulation of extra high voltage (EHV) systems is based on. The reduction of switching surges is therefore an economic necessity. This paper illustrates switching overvoltages resulted from various switching conditions applied to all the existing 500 kV transmission lines of the Electricity Generating Authority of Thailand (EGAT) system. The study is performed with computer transient simulations using the PSCAD/EMTDC program. Details of the system modeling are outlined. The appropriate representation for the various components such as transmission lines, transformers, equivalent sources, shunt reactors, surge arresters and circuit breakers has been chosen. Switching representing the two most severe causes: line energization and line re-energization due to faults i.e. single phase to ground and three phases to ground are considered. Results are analyzed in this paper.