ANALYSIS OF VERY FAST TRANSIENT OVERVOLTAGE IN TRANSFORMER WINDING

Owing to 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 t he multiconductor transmission-line theory. The analysis is conducted in two steps in the frequency domain: first the whole transformer wind ing is simulated using a single transmission-line model, and secondly, the phenomena in the first coil are analysed using a multiconductor t ransmission-line model. The numerical results for an actual 525kV tran sformer conform with the experiment. The interturn voltage shows a res onance determined by the travelling waves in the coil. The propagation of travelling waves is visualised using time domain analysis.