Determination of distribution function of inrush current in three phase transformer using Monte Carlo method

Inrush current encountered during the switching of transformers, are non-sinusoidal, high magnitude currents generated due to flux saturation in the core of transformers during energization. In this paper, distribution function for inrush current in three phase transformers (transformer bank) is obtained using Monte Carlo method. The transient simulation and switching (by statistical switches) of transformer is done using EMTP and MATLAB. Exact types of saturation (anhysteretic) curves with three different amount of residual flux, are taken into account for the cores and the closing time of switching is considered variable with both uniform and normal distribution functions. As a result, the histograms for inrush currents are achieved and a distribution function is fitted to each histogram. These functions can be useful in transformers protection systems.