Loss of mains detection for embedded generation by system impedance monitoring

Abstract

Embedded generators operating in parallel with the electricity supply network are required by law to fit 'loss of mains' protection. This paper presents a new technique for detecting loss of mains based on the measurement of power system impedance and overcomes the deficiencies of more popular relays. The unit's decision to trip is based on the identification of the change in impedance that occurs at a private generator's site when it becomes disconnected from the mains supply.