Mitigating 161 kV electromagnetic potential transformers´ ferroresonance with damping reactors in a gas-insulated switchgear

This study presents a successful mitigation experience of ferroresonance (FR) with damping reactors (DR) involving electromagnetic potential transformers (PT) of a 161 kV gas-insulated switchgear (GIS) in Taiwan. PTs have a typically low thermal capacity and high accuracy because of their measuring functions. Low core losses are necessary to obtain high accuracy, but they also reduce its damping ability and therefore increase the possibility of FR. FR happened twice and destroyed PTs for half a year in the study case. Complete FR waveforms of 161 kV PT were obtained via field tests never conducted before in Taiwan. The first field test had a reappearing FR which sustained up to 22.9 s in 11 random operations and the second one confirmed the validity of DR which shortened FR <;3.9 s in 12 random operations. A reliable prediction by EMTP/ATPDraw simulation and a useful mitigation method with a proper DR were proved by both field tests and the following 23 months satisfactory operations for 82 times since November 2008. It would prove valuable for further research in higher grade voltage GIS.