A novel application of the fast Fourier transform to high-voltage impulse testing of transformers

A method for computer-controlled impulse testing and evaluation of transformer windings is described. Companion software which can be run on any IBM-compatible microcomputer is also described. The method is based on the use of a high-resolution digitizer, eliminating the need for visual interpretation of impulse test oscillograms. Availability of the digitized waveforms permits rapid automated comparison of the impulse response and its frequency domain characteristics with ideal references, the latter through the use of the fast Fourier transform (FFT). Preliminary results indicate that faults involving only a single turn can easily be detected by this method in several ways-from the real or imaginary part of the FFT of the current waveform, from the magnitude of the FFT, or from the phase angle of the FFT. However, the real part appears to be the clearest indicator of the group. The method also appears to permit pinpointing the location of the fault within the transformer winding