Modelling of the impedance frequency response of transformers at no load and under nominal conditions

The need for models that represent the behaviour of transformers operating in steady state or submitted to transient events is of great importance in studies involving power systems. In this context, this study presents a model used to represent the impedance frequency response of transformers at no load and under nominal conditions. In the model, networks of parameters with RLC cells are employed to reproduce the resonances present in the frequency responses and also RL network sections are used to represent the frequency-dependent effects in the core, which aid in the current damping during transient events. The parameter values of these networks are determined with the least-squares numerical method. To evaluate the model as well as the methodology to determine the parameter values, data originating from measurements of the frequency responses with frequency range from 10 Hz to 2 MHz of two single-phase transformers (16 kVA and 55 MVA) are used. Validations of the model are carried out in the frequency and time domains. The model can be used to simulate transformer operation under nominal conditions of voltage and frequency and also for a broad frequency spectrum.