Power Balance Requirements for Sustained Islanding of Inverter Based Distributed Generation

Active and reactive power must be balanced between generation and load when there is a section of the area electric power system that has been disconnected, or islanded, for there to be a possibility of creating a sustained island lasting two seconds or more. The degree to which this power balance must be achieved can be expressed using several equations. These equations can be used to estimate the island voltage and frequency based upon the generation and load conditions that existed just prior to formation of the island. These equations apply to inverter based current source generation and are fundamentally different than if the island were formed using synchronous voltage source generation. Qualitative consideration of advanced inverter functions such as Volt-Var, Frequency-Watt or Volt-Watt are provided. It is proposed that Volt-Var operation will significantly reduce the possibility of sustained island operation.