Switching Surge Characteristics in Gas-Insulated Substation

This paper has investigated switching surge characteristics in low-voltage control circuits transferred from main circuits of gas insulated substations through measuring voltage transformers (VT) and current transformers (CT) based on field measurements and EMTP simulations. The oscillating frequency of the switching surges in main circuits ranges from some MHz to some 10 MHz, and the surge voltages on a control cable are from some 10 V to 300 V in the EMTP simulation. The simulation results agree with the field measurements of the oscillating frequency ranging from 2 MHz to 80 MHz, which don´t support the IEC 61000-4-12 recommended frequency 100 kHz and 1 MHz. The measured voltages range from 10 V to nearly 500 V. Mutual coupling between the main circuits and the control cable induces a high frequency oscillating voltage which are superposed on the transferred voltage. Grounding the both ends of the control cable metallic sheath produces another oscillation due to a circulating current in a closed loop composed of the sheath and the grounding circuit.