Measurement and computation of transient recovery voltage of transformer limited fault in 525kV–1500MVA three-phase transformer

Transient recovery voltage (TRV) in a 525kV-1500 MVA transformer of the three-phase-in-one-tank type was measured. It was proved that TRV can be measured by interrupting the current generated by discharging a capacitor of low voltage through the transformer. The current was interrupted at its zero point by a semiconductor diode at a low voltage. To compute the TRV, a transformer equivalent model composed of an L-C multi-mesh circuit was developed. The TRV waveform computed using the transformer equivalent model agreed well with the measured TRV waveform. The difference among the TRV of the first, second and third pole interruption was explained by the computation with the circuits of symmetrical component method. The transformer inductance that determines the TRV did not have frequency dependency up to the rage of about 20 kHz of the TRV frequency.