Assessment and Mitigation of Temporary Overvoltages on Distribution Feeders with High Penetration of Distributed Energy Resources

Distributed Energy Resources (DERs) are proliferating in distribution systems across most jurisdictions. As distribution system operators work towards interconnecting DERs, they experience new issues that require thorough assessment and mitigation. Among these issues, one such example is coping with intensified Temporary Overvoltage (TOV) on un-faulted phases that results from a system reconfiguration that causes the distribution system to no longer be effectively grounded. In particular, inverter-based DERs and/or certain preferred step-up transformer configurations lead to worse TOV levels than those experienced in typical distribution systems pre-DER connection. TOVs pose insulators and surge arrestors at risk. Currently, there remains a gap in distribution planning of most jurisdictions in formulating the aspects of performance grounding and adopting simple and practical measures to overcome the challenge. This paper provides an overview and analytical evaluation of TOVs in modern distribution systems with high DER penetration and introduces mitigation options, including assessment and design procedures of effective ground sources. Two real distribution systems of a Canadian electric utility are presented as case studies to illustrate the problem definition and proposed mitigation strategies adopted in the project execution.