TRV under transformer limited fault condition and frequency-dependent transformer model

The TRV amplitude factors of 4kVA and 300kVA transformers under transformer limited fault conditions were measured. The measured factors were 1.4 and were lower than the IEC standard. The frequency response of the transformer impedance was investigated using a frequency response analysis (FRA). FRA measurement graphs showed that the short-circuit inductance value of test transformers gradually decreases along with frequency. From this result, a frequency dependent transformer model was constructed. Simulated frequency response of transformer impedance was in good agreement with measured values. Simulated amplitude factor using frequency-dependent transformer model was 1.5 and is good agreement with measured values.