Phase Comparison Islanding Detection For Distributed Energy Resources

A power system island is a part of the power system grid that becomes separated from the larger power system and, depending on the actual load and local DER output, may continue to function. Islands may occur as substation breakers and Automatic Circuit Reclosers (ACR) are opened, and power system faults are cleared, separating local demand and generation from the utility’s power system. Unintended islanding detection and prevention is an important part of interconnecting Distributed Energy Resources to an Area EPS. IEEE 1547 – Standard for Interconnecting Distributed Resources with Electric Power Systems, recommends that an unintended island be detected and removed within two seconds of an occurrence. Islanding prevention has several benefits, some of which are worker and public safety, utility and consumer equipment protection, power system reliability and stability. Mitigation of out-of-phase reclosing and unintended islanding is a challenging part of power system protection. There are several methods that are used to detect an island condition. Localized active and passive methods are beneficial but become less effective in certain circumstances, for example on highly penetrated circuits with multiple types of DER sources. Communications assisted methods are effective at mitigating this risk but require reliable communications infrastructure. For the purpose of this paper we will focus on communications-assisted detection. Communications-assisted detection has some advantages over localized active and passive detection methods. There are several different types of active and passive detection but typically each may have a significant Non-Detection Zone (NDZ) or hysteresis in order to compensate for false positives. With communications-assisted schemes, the NDZ can be significantly reduced while still keeping false positives at a minimum. There are different types of communications-assisted unintended islanding mitigation techniques, most common is conventional Direct Transfer Trip (DTT), but also Phase Comparison detection. This paper focuses on the Phase Comparison detection method. The Phase Comparison detection method offers some unique advantages over conventional Direct Transfer Trip especially when used with complex DER interconnections that include combinations of rotating machine generation and inverter-based DER, or when multiple sources of islanding exist. The main benefit of the Phase Comparison detection method is the reduction of the number of communications channels required. This greatly reduces cost and complexity while still providing the benefits of a communications-assisted scheme.