Underfrequency load-shedding scheme for co-generators connected to an unreliable utility system

The authors describe a load shedding scheme for an existing cogeneration system interconnected to an unreliable utility. The various considerations involved in the design are presented. A full-scale transient stability program was used as a design tool. Extensive studies were carried out to select three-stage load shedding scheme that optimized overall performance. Many factors related to the load shedding scheme, including frequency settings, underfrequency limits, tripping of neighboring utility generation, directional power flow, and antimotoring, were examined. Since the overload could exceed 100%, an exceptionally fast load shedding scheme was developed