Behaviour of transformer windings under surge voltages

A model based on ladder networks for representing transformer windings is given. The development of the model to represent transformer windings is based on a set of ordinary differential equations (ODEs), the solution of these ODEs are carried out by the Runge-Kutta method. The advantage of the model proposed here is that the solution of the ODEs completely describes the behaviour of the transformer windings under transient voltages. Hence the efficiency of calculation is greatly improved. The models available in the literature arrive at similar results by analysing the behaviour of transformer windings to a unit step voltage and then applying the Duhame integral. In the present work the variation of both longitudinal and radial stresses have been investigated, when the windings are subjected to a variety of surge voltages. It is shown that while the longitudinal stress is not very sensitive to the variation of chopping time, the radial stress reaches very high levels. It is shown that these high radial stress values are reached at chopping times of the order of between 7 μs and 9 μs