Loss of mains detection for embedded generation by system impedance monitoring

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