Measurement And Analysis Of VFTO In a 750kV Substation

Disconnector operations in GIS may generate very fast transient overvoltage (VFTO), which is characterized by its high peak value, short rise time, and high frequencies. Mostly, researches on VFTO are focusing on the apparatus involving in the active circuit. However, VFTO may pass through open devices by electromagnetic coupling. To measure VFTO under this situation, lots of field experiments have been carried out in a 750 kV substation. VFTO is measured at the test tap of the high voltage reactor bushing, using the sensor we developed. In one of the experiments, the breaker is kept open, VFTO is generated by disconnector operations (in AIS) on one side of the breaker and measured on the other side. Results show that under this situation, VFTO could reach the peak values of about 55 kV and - 70 kV, the main oscillation frequencies are about 236 kHz, 535 kHz and 1.59 MHz. To verify this case further, computer simulation has also been carried out in the laboratory with the help of ATP. The results agree with each other well.