Transformer winding movement and fault detection

The author discusses the frequency response analysis tests for transformers. The frequency response of a winding is a function of the series and shunt capacitances and inductances between individual turns of the winding and from the winding to earth. These impedances and the frequency response change if the winding, or part of the winding, is displaced. There are two distinct methods of measuring the frequency response of a winding. The first is to apply a low voltage impulse to the winding and digitally record both the applied impulse and the response at the remote end of the winding. Both records are transformed into the frequency domain using a fast Fourier transform and the ratio of the two gives the frequency response. The second method is to apply a swept frequency sine wave signal to one end of the winding and to record the relative amplitude and phase of the resultant signal at the other end of the winding using a network analyzer