Abstract
Safety margin of internal insulation of power transformer windings should be selected to be the minimum necessary level by considering dielectric stresses not only under acceptance test but also under surge overvoltages of transmission systems. There is no practical way to measure the internal stress distributions of a transformer in service. However, such transient distributions can be simulated with a surge transient waveform measured in a substation and a transfer indicial response based on a measurement on the transformer under an untanked condition. This process consists in deconvolution of a measured response waveform by an excitation input waveform to obtain the transfer indicial response and convolution of the response with the surge waveform. The resulting waveform represents an estimated transient voltage which appears across the winding section when the surge will be applied to the transformer. A computer program for a workstation is developed and it is validated for its practical applicability through numerical processing examples of actually measured data at IREQ in Canada.
