Switching Surges in Transformer Provoked by Sequential Tripping of Circuit Breakers

A study of switching surges in a 400/110 kV substation was carried out in order to detect the causes of severe damage to the power transformer, which happened after a busbar fault. The busbar protection generated tripping signals for several circuit breakers and after their sequential tripping, the surge arresters installed on the 10.5 kV stabilizing windings inside the transformer were destroyed. The computer simulations were carried out on an appropriate model, which was developed for the study. The comparison between the recorded and computed fault currents showed good correspondence. Overvoltages of small magnitudes occurred on all three voltage levels: 400 kV, 110 kV and 10.5 kV. The energy generated by overvoltages was below the nominal value of the absorption capacity of the surge arrester installed on the stabilizing windings and the inspection of the arresters showed their defective characteristics.