Determining Ideal Impulse Generator Settings from a Generator-Transformer Circuit Model

Impulse testing of large power transformers is a routine test, which is designed to mimic a lightning strike in service. At the design stage, it is useful to have a detailed circuit model of the transformer in order to simulate the impulse test and to check for possibly damaging voltage stress levels. In our model, which includes capacitive and inductive couplings as well as resistive effects, we apply an ideal full or chopped waveform to the impulsed terminal. In an actual impulse test, it is sometimes difficult to approximate the ideal waveform, particularly the full wave one, and a trial-and-error approach is often taken. Here we describe an approach that couples a circuit model of the impulse generator with a transformer circuit model and show how, from this combination, we can arrive at close to ideal settings for the generator, provided such settings are possible.