Response of Transformer Windings to System Transient Voltages

Some recent transformer failures have been attributed to part-winding resonances excited by a form of switching surge voltage pulse which produced internal overvoltages. This paper takes a tutorial approach to relate a transformer winding to an equivalent electrical network which can exhibit resonant effects both at its terminals and internally. The relationship between the resonance phenomenon and pulse response is explained and illustrated with practical examples for the standard test waveforms. A proposed alternative switching surge waveform is examined for its effect on the internal response of transformer windings. The material presented should promote the understanding required for consideration of changes in standard test waveforms.