A procedure for derating a substation transformer in the presence of widespread electric vehicle battery charging

This paper studies the effect of electric vehicle (EV) battery charging on a substation transformer that supplies commercial, residential, industrial, and EV load on a peak summer day. The analysis begins by modeling non-EV load with typical utility load shapes. EV load is modeled using the results from an analytical solution technique that predicts the net power and harmonic currents generated by a group of EV battery chargers. We evaluate the amount of transformer derating by maintaining constant daily transformer loss-of-life, with and without EV charging. This analysis shows that the time of day and the length of time during which the EVs begin charging are critical in determining the amount of transformer derating required. Our results show that with proper control, EV charging may have very little effect on power system components at the substation level.