Power based algorithm to provide loss of grid protection for embedded generation

The paper introduces a new protection algorithm designed to detect when the connection between an embedded generator operating and the utility grid is lost. Once loss of grid is detected, the intertie circuit breaker connecting the embedded generator to the utility should be opened to allow the orderly restoration of supply to other utility consumers. Failure to detect the loss of grid and subsequently open the intertie breaker could result in utility consumers receiving a low quality supply and could expose the embedded generator to severe damage should the utility grid be reconnected while out of synchronism with the embedded generator. The paper describes the basis for the operation of the protection algorithm and the role of the various elements together with the derivation of the tripping criterion. Its response to a series of power system switching scenarios are presented, including loss of grid, independent operation, out-of-phase reclosure, parallel operation together with a selection of fault studies, and for each it is shown to operate as required.