We have recently energised a section of Almond (35mm2) powerline at 33kV via single phase fuses. The feeder powerline was live when we energised. We have blown 5 surge arrestors over three days. They split open and caused all three fuses to open at the feed end (125A fuses). We were told that this seems to be ferro resonance and the problem can be solved by using a three phase fused pole mounted isolator. The surge arrestors had a MCOV of 24.4kV and the 33kV source is solidly grounded. Does the ferro resonance theory seem feasible? PS: We have had no surge arrestor failures on the sections of 33kV powerline that were energised via three phase circuit breakers.
Kevin Bosch
Rainbow Technologies
Kevin Bosch
Rainbow Technologies