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 chargin g on a substation transformer that supplies commercial, residential, i ndustrial, and EV load on a peak summer day. The analysis begins by mo deling non-EV load with typical utility load shapes. EV load is modele d using the results from an analytical solution technique that predict s the net power and harmonic currents generated by a group of EV batte ry chargers. We evaluate the amount of transformer derating by maintai ning constant daily transformer loss-of-life, with and without EV char ging. This analysis shows that the time of day and the length of time during which the EVs begin charging are critical in determining the am ount of transformer derating required. Our results show that with prop er control, EV charging may have very little effect on power system co mponents at the substation level.