Switching surge characteristics in a gas-insulated substations in particular reference to low-voltage control circuits

The paper describes EMTP simulations of switching surges in a gas-insulated substation, and investigates the oscillating frequency and the surge transferred to a low-voltage control circuit cable through a measuring voltage-transformer (VT). It has been found that the oscillating frequency of the switching surge exceeds 1 MHz, which agrees with field measurement results, and is, in general, dependent on the total length of gas-insulated buses and on the distance from an operating circuit-breaker or a disconnector to a node where a switching surge is observed, i.e. a VT. The voltage waveform at the VT secondary circuit becomes oscillatory, and the oscillatory waveform is distorted as it travels down to the end of a control cable. Thus, the frequency of the oscillatory waveform at the cable end is lower than that at the VT secondary terminal.