Communication assisted protection selectivity for reconfigurable and islanded power networks

Distribution power system islanding will involve significant grid reconfiguration, especially if maximum flexibility of operation is to be achieved. Protection selectivity will be a challenge because of the associated changes in fault conditions, and is further complicated by distributed generator fault characteristics. This paper proposes a three-stage communication assisted protection selectivity strategy for reconfigurable distribution networks. Level-1 provides fault detection and protection based on local measurements; Level-2 employs inter-breaker communications; and Level-3 adapts relay settings by communicating with a supervisory controller. Protection selectivity is improved by the adoption of each successive level. Fundamental to this strategy is that it must be designed to operate over, and be tolerant to the inherent deficiencies of, cost-effective Internet Protocol communications.