Owing to the operation of the disconnector switch very fast transient overvoltages can generate a voltage oscillation inside the transformer connected to it. A practical method to analyse the oscillation is developed based on the multiconductor transmission-line theory. The analysis is conducted in two steps in the frequency domain : first the whole transformer winding is simulated using a single transmission- line model, and secondly, the phenomena in the first coil are analysed using a multiconductor transmission-line model. The numerical results for an actual 525kV transformer conform with the experiment. The interturn voltage shows a resonance determined by the travelling waves in the coil. The propagation of travelling waves is visualised using time domain analysis.
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