Transients during 138 kV SF6 breakers switching of low inductive currents

The effects of switching low inductive currents with 138 kV SF₆ breakers in a petrochemical plant are discussed. Switching transients are believed to have contributed to the failure of a 13.8 kV PT and a 13.8 kV air magnetic circuit breaker. The high-frequency transient surge can transfer across a transformer due to transformer capacitances between the high and low-voltage windings. The electromagnetic transient program system model and different case studies are discussed with the effect of different transformer winding capacitances. The interruption mechanism of low inductive currents is described. This analysis demonstrates the need to conduct switching transient studies and the need for surge arresters on transformer secondary terminals under certain system conditions