Impacts of High Penetration of Single-Phase PV Inverters on Protection of Distribution Systems

In line with global efforts to achieve 100% renewable energy targets, it is expected to see significantly higher ratio of inverter-based resources (IBRs) integrated into distribution systems. The impacts of high penetration of IBRs on distribution systems has become a critical consideration for utilities to further investigate. Currently, a large percentage of IBRs are distributed roof-top behind-the-meter PV installations which utilize single-phase PV inverters.The existing PV inverters connected to distribution feeders are a combination of legacy and smart inverters. Legacy inverters are the traditional inverter technology with settings and capabilities that follow RULE 21–2003 version. However, the latter generation as called Smart Inverters incorporates specific functions (following the latest version of Rule 21 (after September 2017)) that are intended to support grid and achieve higher penetration.This paper presents a summary of observations from a series of studies with focus on analyzing the impact of high penetration of single-phase smart and legacy PV systems on the existing feeder protection systems. A representative SCE’s distribution feeder was modeled in the PSCAD/EMTDC software and used as a benchmark to perform different scenarios. The remarkable increase in the penetration of solar PV systems, exceeding annual peak load of the feeder was shown to create several protection challenges due to bi-directional power flow and change in fault current level seen by protective elements. A comparative analysis of fault current seen by the feeder protection system with a mix of Distributed Energy Resources (DERs) at different penetration levels is done in this study. Key takeaways from various simulation studies are described.