Automatic local state detection for synchronous distributed generators

In order to avoid unnecessary loss of supply especially for high priority loads, distributed generators (DGs) stand-alone operation is getting more attention. However, to ensure more reliability, the islanded distribution network must reconnect to the grid as soon as the quality of supply from grid is refined. As the circuit breaker (CB) which had been opened for unintentional/intentional islanding operation is often kilometers far from the DG, introducing a reliable method for localized reconnection detection and proper DG control mode activation will be an interesting issue. Such a method could be implemented via a micro-processor based relay as a low cost alternate for the expensive communication means required between all of the CBs that may initiate the islanding and the DG. In this paper a suitable procedure to provide reconnection detection signal for synchronous type DGs is presented. The procedure is based on governor signal processing.