A multi-function relay for loss of mains protection

Loss of mains refers to the situation where an embedded generator´s site is isolated from the main source of the public electricity supplier (PES) due to a switching operation. In this case, the site could be left connected to part of the PES customer load and operate as an independent power island. The inter-tie circuit breaker should be tripped at the coupling point between the embedded generator´s site and the PES system so that orderly restoration of the supply can be achieved. It is also essential to trip the inter-tie circuit breaker to ensure that the local PES loads are not supplied with power whilst the network is unearthed. With numerical relay technology, it is possible to produce a multi-functional relay that includes comprehensive protection functions for loss of mains, basic protection functions for the feeder and protection for the embedded generator. Ancillary functions, such as circuit breaker control and monitoring, measurements, recording, remote communications and self-checking can also be provided as expected from a modem numerical relay. This paper details how GEC Alsthom has extensive knowledge regarding the design and manufacture of such multi-function numerical protection such as the LGPG111, K series and LFZR relays