A new power transformer model over wide frequency rang for EMTP

A new method for power-transformer modelling over a wide range of frequency up to 1 MHz is presented in this paper. The goal is to develop an appropriate model for transient investigations and insulation-coordination studies in power systems. The Model provides suitable facilities for power system operators and is based on the measurement results in the frequency-domain from 10 Hz up to 1 MHz. The work focuses firstly on a new explanation of the power transformers behavior in the frequency domain and finding a structure in a RLC network form which can easily be applied in EMTP. In order to understand the transformer behavior in frequency domain, the transformers frequency response is analyzed in detail. According to the electromagnetic properties of the materials used in transformers, a structure of the RLC network is determined. The structure contains several elements presenting the electrical phenomena in transformers (e.g. the iron core ferromagnetic property and capacitive coupling between windings). In the next step, the parameters of the chosen RLC structure are estimated with the aim of achieving a proper coincidence with the measurement results. For this purpose, EMTP is linked to MATLAB using a new procedure with an appropriate performance. To prove validity of the proposed model in transient studies, the transformer response for low impulse voltage is measured and compared with the simulation results. A good accordance with the transient measurements is demonstrated.