Low-cost under-frequency relay for distributed load shedding

An under-frequency load shedding relay utilizing a single-chip microcomputer is described. The device may be used to shed off-peak load, thus replacing expensive emergency reserve over the corresponding periods. Economic analysis shows that the device is cost-effective when controlling loads with an installed capacity greater than about 20 kW. Use of an existing contactor, associated with a radio teleswitch for example, would reduce the cost of the relay and further improve the economic case for this application. The savings which accrue from the proposed approach increase with the installed capacity of the controlled load. Application to a limited number of large off-peak installations could replace a significant amount of emergency reserve in an isolated supply system at modest cost