Three-Phase Distributed Model of High-Voltage Windings to Study Internal Steep-Fronted Surge Propagation in a Straightforward Transformer

A three-phase distributed constants model for high-voltage windings of a transformer is presented. The mutual couplings between phase coils are considered introducing some approximations. Applying the Clarke transformation to the proposed model, the voltage and current surge waves are provided by a simple numerical method. In this way, the model can be used to design the insulation between the turns of a single coil and between the windings and the iron core. A comparison of the numeric results obtained by applying the proposed method with the results obtained by other authors confirms the validity of the model. Moreover, further results are obtained: the proposed approach allows also finding the voltage and current waveforms for asymmetric faults.