1998 Volume 118 Issue 4 Pages 381-388
A field test was carried out to investigate a fault clearing transient due to current interruption of a 3-phase to ground fault at the secondary side of a 3MVA, 22/6.6kV transformer by a vacuum circuit breaker. EMTP simulations in comparison with the measured results have made it clear that the capacitance Cp of a CR divider to measure voltages reduce dv/dt of a transient recovery voltage across the circuit breaker by the ratio of C1 / (C1 + Cp) where C1 the transformer stray capacitance. The leakage inductance evaluated from the transformer rating has been found noticeably greater than that determined from the measured fault current possibly due to the transformer saturation. Considering a transformer magnetizing conductance and selecting an appropriate interrupted-current, an EMTP simulation gives a satisfactory result compared with a field test.