Determining the HV insulation strength by insulation coordination based on electrical stress situation

摘要

This article aims to determine a proper voltage rating known as the withstand capability of HV equipment in a 115 kV air insulated substation in Thailand because some of the HV equipment were severely damaged by high switching transient overvoltages. Then, this case was investigated by using a simulation model in the ATP/EMTP. Actual data acquired from all the equipment or derived from physical dimension of equipment was used as input parameters in the simulation model. In different switching operation cases as load rejection, earth-fault, capacitor bank switching etc., the maximum overvoltage was obtained from the simulation and subsequently applied in the insulation coordination procedure. The systematic modeling to evaluate electrical stress and insulation coordination process were thoroughly expressed to simplify the process for utility applications. Finally for this 115 kV substation, the short duration withstand voltage of 275 kV and the lightning impulse withstand voltage of 650 kV were selected from the insulation coordination and practically applied to determine the minimum electrical clearance of HV equipment for both phase-to-earth and phase-to-phase distances.