Impacts of Electric Vehicle Charging on Electric Power Distribution Systems

Robert Bass, Portland State University


Electric Avenue, located on the PSU campus along SW Montgomery Street, is a joint project between Portland General Electric, Portland State University (PSU) and the City of Portland. Launched in August 2011, Electric Avenue is intended as a research platform for understanding the impact electric vehicles have within the larger context of the city. For this research, we used Electric Avenue to investigate the impacts electric vehicles (EVs) may have on electric power distribution systems. Nonlinear loads, such as EV chargers, will often introduce power quality (PQ) issues within distribution circuits, which can have detrimental effects on system components. PQ encompasses several specific concepts such as harmonic distortion, DC offset, phase imbalance, and voltage deviations, among others, and these are quantified in myriad ways. For this study, we focus on harmonic currents since these have the potential to affect the lifetime of magnetic assets such as distribution transformers and instrument transformers. Utilities plan asset management by anticipating the nature of loads and selecting assets designed to handle those loads. A deeper understanding of these matters specific to EVs will aid utilities in the design of distribution systems and provide guidance for asset planning. A load's PQ affects magnetic assets because of the potential for insulation failure and core saturation. Understanding the PQ of nonlinear loads assists distribution engineers with the selection of k-factor ratings for distribution transformers, selection of CTs and VTs, protection settings and decisions regarding conductor ampacity. For this study, we measured the PQ of EV chargers, paying specific attention to total harmonic distortion (THD) of individual EV chargers and total demand distortion (TDD) of the Electric Avenue service. We also noted phase imbalance, phantom loading and other PQ issues observed during the course of our study. Our objective is to expand the electric utility industry’s understanding that EVs have on these issues.

Project Details

Project Type:
Project Status:
End Date:
September 30,2013
UTC Grant Cycle:
OTREC Small Starts
UTC Funding: