A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Energy, School of Environment, Resources and Development

Thesis (M. Sc.) - Asian Institute of Technology, 2012

The variety advantages of electric vehicles (EV) in cooperate with the support from the government will stimulate the electric vehicles to penetrate into Thai mobile market. However, all EV s require connecting with the national grid for recharging their batteries, the impact of their charging have to be assessed in order to prevent the power system problem. The distribution transformers are the prior infrastructures that will confront with the critical risk of being overload. The ultimate objective of this thesis, therefore, was to assess the potential overloading impact of the electric vehicles charging on the distribution transformers of Provincial Electricity Authority (PEA), the main distribution utility of Thailand. Chiang Mai metropolitan, the center of northern region of Thailand that has potential to adopt EV, was selected to be the study area. The te1m overloading in this thesis refers to the load that go beyond 80% of rated capacity, namely the 80% trigger threshold set by PEA. The utilization factor and the number of houses per transformer are the main parameters to identify the permit level EV adoption and the critical transformers that will be overload at each adoption level. From the simple statically methodology, the thesis reveals that in case of charging during peak hour, at 15% adoption level, the proportion of critical transf01mers are fifty-two percent and f01ty-eight percent for 160 kVA and of 250 kVA distribution transformers respectively. However, if the trigger threshold was increased to be 100%, the critical transformers could be reduced to be six percent and ten percent respectively. Besides, in case of charging during off-peak hour strategy, it was found that at 15% adoption level; no transformers would be overloaded. At 25% EV adoption level, less than ten percent of total distribution transformer would be overloaded. This result will acknowledge the distribution utility to plan the asset management due to the coming of electric vehicles in near future.