A simplified method for estimating voltage dips due to transformer inrush

This paper describes a simplified method for the calculation of the voltage dips based around good engineering practice, and the typical data available from small transformer manufacturers. The simplified method is implemented within the transient stability module of an industry standard power system analysis program. The paper also shows an approximate rule of thumb that can be used to estimate the maximum transformer capacity that can be connected at a specified fault level without exceeding a specified voltage dip. The simplified inrush model is validated against site measurements for a single 1.6MVA wind turbine transformer being energised on a weak 33kV network. The validation shows that although there are some quite general assumptions made within the simplified model, it still provides sufficient levels of accuracy for the required purpose.