A method for modeling nonlinear core characteristics of transformers during transients

An EHV transformer´s insulation system must be designed to withstand stresses generated during transient events. Computer models are employed for predetermination of these stresses. The lack of accurate and consistent computer models for use by both utilities and manufacturers, is felt to contribute to the relatively high failure rate of EHV transformers. This paper develops a detailed nonlinear transformer model and a solution method that improves the accuracy with which the effect of the nonlinear characteristic of the magnetic core during transients can be predicted. This model is based on linearization of the core´s saturable characteristic during solution time intervals. This paper describes a nonlinear, single phase, detailed transformer model and its verification against measured data