Chopping of Transformer Magnetizing Currents Part I: Single Phase Transformers

Abstract
A Transformer model for chopping overvoltage calculations is presented by a mathematical description of transformer magnetics-eqs. (1) and (2) and also by an equivalent circuit. The model is based on eddy current losses in laminations with static hysteresis neglected. The empirical constants of the model are determined from 60Hz measured BH loops. The dynamic BH loops; the dynamic BH transients of the core can be represented with good accuracy. Maximum chopping voltages across the range of transformer ratings are calculated without breaker limiting action. The model is suitable for computer studies of overvoltages where breaker characteristics and network elements are represented. Extension of the concept for three phase transformer applications is continued in Part 2.

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