Unintentional islanding in distribution grids with a high penetration of inverter-based DG: Probability for islanding and protection methods

Abstract

Unintentional islanding in distribution networks due to the presence of DG is one of the major safety concerns for the grid interconnection of generators. The present paper looks at the current protection and safety requirements and new activities in selected European countries with a focus on inverter based generation. By means of a field study carried out in a real LV network with a high DG penetration, occurrence and persistence of balanced load/generation conditions - which are the basic prerequisite for islanding - are analyzed and the according probability is calculated based on different penetration scenarios protection settings and load characteristics. The results show that under realistic conditions the probability to encounter an island is not negligible. Thus additional protection methods to the standard voltage and frequency monitoring are required in order to detect a loss of mains at the generator and ensure the safety of customers and maintenance personnel.