Dynamics of high penetration photovoltaic systems in distribution circuits with legacy voltage regulation devices

Abstract

Concerns for criteria pollutant emissions and air quality, as well as greenhouse gas emissions, have resulted in stringent energy and environmental rules and regulations mandating deployment of renewable resources. Moreover, increased frequency of extreme weather events highlighted the need for increased reliability and resiliency of the grid further encouraging deployment of distributed energy resources. This has resulted in an increasing deployment of solar PV in the distribution system. While many studies focus on analyzing the impact of increased penetration of PV on smart circuits or systems with upgraded infrastructure, it is necessary to assess impacts on existing circuits with legacy devices. In this study, the impacts of high penetration of PV are investigated for two distribution circuits (one residential and one commercial) located in northern California, equipped with legacy voltage regulation devices including on-load tap changer (OLTC) transformers and switched capacitor banks.The dynamics of circuit operation and bus voltage profiles are studied by developing time-resolved three-phase balanced feeder models of the two circuits. Using connectivity and load demand measurements provided by the utility, the models are validated and calibrated to the point of the substation. In order to help generalize the results associated with the two circuits, a set of circuit design metrics are developed to characterize the distribution of the load demand and generation, load center (LC) and generation center (GC). The load center and generation center metrics are weighted averages of the total consumed and total produced bus energy relative to the distance from the substation.Various scenarios are simulated in order to quantify generation limits necessary to conform to various standards including ANSI C84.1 voltage standards while maintaining reliable circuit operations. In these scenarios, location of the PV installation as well as PV penetration (from baseline to 100%) are varied. Simulation results indicate that high PV penetrations have a direct impact on OLTC transformer operation but only marginal impact on capacitor switching. Tap operation is found to increase approximately linearly with PV penetration for both of the circuits and specific Load Drop Compensation (LDC) controller settings greatly affect the sensitivity of OLTC operation to PV penetration. It is also concluded that not only the location of PV installation relative to loads and substation affects the performance, the metrics developed are a powerful tool to describe high PV circuits and to help utilities better plan for deployment of PV in their distribution network.