Application of the transfer function method to transformer impulse test

摘要

For the impulse testing of transformers, the transformer currents for impulses at different voltage levels are compared for a fault check. However the impulse waveforms may be different and this possibility makes the comparison difficult and the result is sometimes dependent on an engineer's judgement. By applying the transfer function (TF) method, this comparison becomes independent from applied voltage waveforms because their transfer functions are compared. Usually the fault check comparison is discussed in the frequency domain and minor local fault pulses have been reported to be difficult to detect because their spectra are small and wide. This paper proposes a method which still has the independent characteristic from applied voltage waveforms and can detect local faults by applying the TF method not in the frequency domain, but in the time domain because such local pulses may be possible to detect in the time domain when they are large enough. The proposed method consists of the following three steps. Firstly, a TF is computed for the reduced voltage level by deconvolution. Then a test current waveform for the reduced voltage waveform is corrected for the test voltage waveform by convolution. Finally, a measured test current waveform for the test voltage is compared with the corrected current under the same test-voltage-waveform condition.