Effects of parasitic transformer capacitances on switching transients at a HV capacitor bank

ATP-EMTP simulations were conducted to investigate the cause of failure of a 4.5 MVAR capacitor bank at a high voltage switching station. To include the possible role of ferroresonance and other high frequency resonance effects, models of the 161 kV/34.5 kV transformer and the circuit breaker at the switching station included non-linear inductance and various appropriate parasitic capacitances. The simulation results for the capacitor bank phase currents and their Fourier frequency spectra suggest that excessive switching transients due to resonance effects involving transformer high voltage earth capacitance and inter-winding capacitance, rather than ferroresonance, may be associated with the capacitor bank failure.