Ageing Evaluation of the Distribution Transformer under Varying Load due to Electric Vehicle Charging

Abstract

Electric vehicles are expected to offer many benefits over conventional vehicles, such as reduction of carbon emission and fuel costs. However, the adoption of electric vehicles would bring great challenges to the distribution transformer, as their charging behavior would make the transformer operate under the varying load and therefore submit to overload risk. Hence, the insulation aging which shortens the transformer lifetime would be accelerated. In this research, we study the impacts of electric vehicle charging on the aging of the distribution transformer with conventional and high-temperature insulations. The number of households, base load and charging habits of a district in Jiaxing city are collected, and then a Monte Carlo simulation model is proposed to evaluate the additional load demand due to the electric vehicle charging. Furthermore, the simulated load demand is input to a model, which is modified based on the algorithm stipulated in IEEE C57.91, to calculate the thermal rise and the aging of the distribution transformer. The results imply that the electric vehicle charging would exacerbate the swing of the load demand. Particularly, the lifetime of the conventional distribution transformer would be significantly reduced. In comparison, the high-temperature insulation could mitigate the negative impacts of the electric vehicle charging on the transformer ageing.