Application of a Probabilistic Approach to Distribution Transformer Derating Calculation

A probabilistic model is used to estimate the fundamental and harmonic contents ofbattery charging load of Electric Vehicles (EV). Regarding this estimated harmonic-rich load,charging station transformer’s K-factor, current THD and the consequent derating is evaluated.The approach considers battery charging start time, state of charge and a worst-case scenariowhich is, uncontrolled charging at the peak load time. Since the employed model is more realisticthan deterministic models, a better understanding of the negative impact of harmonic-richchargers will be provided. Test results demonstrate that EV penetration causes a noticeablechange in the K-factor of the transformer, emerging the need for load management programs incase of high penetration of plug-in electric vehicles.

Keywords:

Electric vehicle , battery chargers , probabilistic modeling , transformer derating , power quality