Computing the internal transient voltage response of a transformer with a nonlinear core using Gear´s method. Part 1: Theory

An EHV transformer´s insulation structure must be designed to withstand the internal stresses generated during transients. Computer models are employed for predetermination of these stresses. This paper develops a detailed transformer model and solution method which represent the nonlinear, saturable characteristic of the magnetic core during transients. The resulting set of stiff nonlinear differential algebraic equations are solved by application of Gear´s method. This paper describes the transformer model and the necessary set of equations based on linearization of the iron core´s saturable magnetic characteristic at each time interval