Utility Distribution and Power Transformer Planning Practices Surveys and Proposed Planning Guidance Considering Future EV Adoptions

Transformers are important components of power grids and valuable assets of utilities. Good planning practices help utilities to properly size, rate, and fully utilize the capacity of transformers and prolong the life of transformers. Projected increasing adoption of electric vehicles and the charging demand may have significant impacts on transformers. Tennessee Valley Authority (TVA), Tennessee Valley Public Power Association (TVPPA), West Kentucky Rural Electric Cooperative Corporation (WKRECC), and University of Kentucky (UK) have performed a study looking at the impact of increasing EV adoption on transformers and proposing possible guidelines on transformer planning practices considering future EV adoptions. We have prepared and conducted two surveys on transformer planning practices in 2023, one for distribution transformers and one for substation transformers, building upon (Electric Power Research Institute) EPRI's surveys. The survey questions include current practices for sizing, rating, and loading, replacement, overcurrent protection practices, Electric Vehicle (EV) and program affecting diversity, use of load and ambient temperature profiles when determining rating, use of advanced monitoring techniques for inspection and replacement, etc. The survey attendees are local power companies of TVA. The survey results will help utilities better understand the current transformer planning practices and develop sound guidelines considering future EV charging needs. This paper presents the aggregated survey results and proposed guidelines for transformer planning considering EV adoptions.