Introducing saturation characteristic fitting techniques for power transformers in the Costa Rican Electrical Network

Many electromagnetic transient studies (i.e. overvoltages caused by ferroresonance) require an appropriate modelling of the transformer iron core saturation characteristic. In the Costa Rican Electrical Network (SEN), an important amount of installed power transformers do not provide the nonlinear flux-current curve, according to their datasheets, making very hard to simulate the impact of the transformer core representation in the electromagnetic phenomenon under study. This paper explores the representation of the magnetization characteristic by a sum of exponentials, a rational function approximation and by arctangent functions in order to evaluate which technique can be implemented in the SEN. In addition, with the support of the Costa Rican Institute of Electricity (ICE) High Voltage Laboratory (LIMAT), the approach for fitting saturation characteristic using arctangent functions is validated in a 1500 kVA three-phase transformer.