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Loss of mains protection (LOM) is among the most challenging issues related to the integration of distributed generation (DG). This paper presents simulation studies on the effect of multiple DG units on LOM protection. The results reveal an operational risk related to the active LOM detection methods. The effect of voltage droop control of the DG on the form of the NDZ is also studied.

This paper deals with an issue that has not received much attention in literature. The aim of the study is to investigate the influence of doubly fed induction generator (DFIG) reactive current injection during a voltage dip on the operation of a wind turbine circuit breaker. The study is done using a novel hardware-in-theloop test environment constructed using two real time simulators (dSPACE and RTDS) and commercial protection relay. It is found in this study that the reactive current injection enhances the operation of wind turbine protection since the zero crossing of the circuit breaker currents is achieved earlier. This action may prevent from failed auto reclosing and other safety hazards. Index Terms--Circuit breaker, DFIG, Fault RideThrough, reactive current injection.

All distributed generating units need to be equipped with an anti-islanding (AI) protection scheme in order to avoid unintentional islanding. Unfortunately most AI methods fail to detect islanding when the islanded load matches with the production in the island. Another concerning issue is that certain active AI protection schemes may cause power quality problems. This paper proposes an AI protection method which is based on the combination of a specially designed reactive power versus frequency (Q-f) droop, and a constantly injected reactive power variation (RPV) pulse. The method is designed so that the injection of reactive power is of minor scale during normal operating conditions. Yet, the method shows high performance during islanding. Simulations were performed with the help of PSCAD/EMTDC in order to analyze the performance of the method. The results indicate that the method is able to detect islanding within 2 seconds even in a perfectly balanced island.