Study on Transient Recovery Voltages for Transformer-Limited Faults

Severe transient recovery voltage (TRV) after current interruption may appear when a fault occurs in the immediate vicinity of a power transformer without any appreciable capacitance between the transformer and the circuit breaker. These faults are called transformer-limited faults (TLFs), that may cause higher rate of rise of TRV than the standard values specified for terminal fault test duties T10 and T30 of IEC 62271-100 and IEEE standard C37.06. TRVs for TLF conditions with large capacity and high-voltage shell-type power transformer were measured by the capacitor current injection method. The impedance frequency response were also measured by the frequency-response analysis (FRA) and then TRVs were reproduced by the simplified transformer model with a series connection of parallel circuit of inductance, capacitance, and resistance evaluated by the FRA measurements. The reproduced TRV showed good agreement with the measured TRV even though deformation from a sinusoidal waveshape was observed due to superposition of higher frequency components on the TRV.