Approaches to Network Protection for Inverter Dominated Electrical Distribution Systems

The use of the micro-grid paradigm with extensive inverter interfaced generation raises the problem of severely restricted fault levels when operating in a power island. This paper presents a review of the conventional distribution network protection practices and then discusses their limitations when applied to inverter dominated micro-grids. The use of voltage measurement based fault detection is considered and is followed by consideration of how to apply this technique in conjunction with an adaptive form of protection. A potential solution for small micro-grids is presented in the form of voltage controlled overcurrent devices to enable the use of lower current threshold settings. Key issues for the design of network protection within micro-grids are summarised.