Prediction of Transient Transfer Functions at Cable-Transformer Interfaces

Lightning and switching surges are the most common causes of electrical failures in distribution transformers. Fast rising transients that reach the transformer can cause large turn-to-turn voltages at the line end of the windings and resonances, which result in large voltages to ground elsewhere in the windings, many of which may exceed the winding insulation strength. In a previous paper, empirical data were presented which indicate that the type of cable employed between the source of the transient and the transformer has an impact on the electrical stress imposed on the transformer. The present contribution takes a more analytical approach to this work, and establishes the factors which play a role in this difference, the most important of which appears to be the loss of the cable dielectric