Modified method for transformer magnetizing characteristic computation and point-on-wave control switching for inrush current mitigation

This paper proposes a new model for the low-frequency transient analysis of a transformer, with a modified equation for calculation of the flux-current characteristic representing the saturation inductance of the transformer. The model is based on the V-I (voltage-current) no-load curves and uses the no-load reactive power losses. To validate the model, it was used to simulate the no-load magnetizing current in steady-state condition, as well as the transient inrush current at network frequency. Evaluation was done both by comparing the simulation results obtained with the proposed model and those available in the relevant literature, and by practical measurements. The experimental results presented in this paper were obtained via a laboratory setup and a data acquisition system based on the dSPACE board 1104. Moreover, a control switching to mitigate the transient inrush current in a transformer was developed and applied experimentally in the laboratory and also in the simulations. This control strategy was performed by taking into account the residual flux at the opening instant of the related circuit breaker. A comparative study was carried out showing the validity of the proposed model and the mitigation technique.