Impacts of substation transformer backfeed at high PV penetrations

Increasing amounts of photovoltaic penetration (PV) on the electric distribution system have given rise to a number of challenges for electric utility companies. One of the more frequent issues utilities will have to address is the potential for a large amount of substation transformer backfeed stemming from reverse power flow on distribution circuits. Excess PV output on the distribution system during periods of minimum daytime loading causes a number of issues for utility planning and operation, such as temporary overvoltage conditions, the need for protection schemes modifications, and equipment failure from an increase in voltage regulation operations. The aim of this paper is to summarize the considerations related to substation transformer backfeed, how it affects common distribution system configurations, and to also touch on opportunities for mitigating the impact of these issues.