Abstract: Sales of privately-owned plug-in electric vehicles (PEVs) are projected to increase dramatically in coming years and their charging will impact residential service transformer loads. Transformer life expectancy is strongly related to the cumulative effects of internal winding temperatures, which are a function of loading. Thermal models exist (e.g., IEEE Standard C57.91) for predicting these internal temperatures, the most sophisticated being the Annex G model. While this model has been validated with measurements from large power transformers, small residential service transformers have been given less attention. Given increasing PEV loads, a better understanding of service transformer aging could be useful in replacement planning processes. Empirical data from this paper indicate that the Annex G model over-estimates internal temperatures in small 25 kVA 65 °C rise mineral-oil-immersed transformers. This paper presents an alternative model to Annex G by using a genetic program. Empirical results using a thermally-instrumented transformer suggest that this model is both simpler and more accurate at tracking empirical transformer data. We conclude that one can use a simple thermal model in combination with data from advanced metering infrastructure to more accurately estimate service transformer lifetimes, and thus better plan for transformer replacement.
Abstract: While there are a number of useful studies on the greenhouse gas impacts of transportation electrification, only recently have researchers begun to understand the impacts of electricity on electric power infrastructure. Thus, the primary goals of this research project were to understand these impacts in detail and to develop new methods for reducing the impact of transportation electrification on the electricity transmission and distribution infrastructure. In particular, this report focuses on understanding and mitigating the impact of transportation electrification on the medium and low voltage distribution infrastructure, through which electricity is transported from the bulk power grid, through neighborhoods, to individual homes and businesses. This project focused specifically on the impacts of electric vehicles on two key components of power distribution systems: residential service transformers, and underground cables. This project also studied new methods to dynamically adjust the number of electric vehicles that are charging simultaneously, in order to mitigate the risk of electricity infrastructure damage from electric vehicle charging.