Analysis of very fast transient overvoltage in transformer winding

Owing to the operation of disconnector switches, very fast transient overvoltages can generate a voltage oscillation inside power transformers connected to them. A practical method to analyse such oscillations is developed based on 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 525 kV power transformer conform with experiments. 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