A method for evaluating the impact of electric vehicle charging on transformer hotspot temperature

The expected increasing market share of electric vehicles is a response to the combination of new technological developments, governmental financial control, and an attitude shift of residents to a more environmentally friendly lifestyle. The expected capacity required for charging, imposes changes in the load to the already existing components in the electric power grid. In order to continue managing these existing assets efficiently during this load change, it is important to evaluate the impact imposed by the battery charging. The transformer is considered as one of the most important components in the grid due to the potential severe and economic consequences upon failure; hence it is reasonable to begin an impact evaluation with this component. In areas where the grid is dimensioned close to the load limit, which often is set by transformer capacity limitations; an additional load from electric vehicles could force investments in the grid infrastructure. This paper presents a method to model electric vehicle charging load, based on uncontrolled and controlled charging scenarios, and furthermore, evaluate the impact caused by these charging scenarios on the distribution transformer hotspot temperature and loss of life using a thermal model.