Underfrequency and Undervoltage Load Shedding in an Industrial Plant with Cogeneration Facilities

Underfrequency load shedding is commonly used in the utility systems when AGC (Automatic Generation Control) cannot keep pace with the load demand and the stability of the generators can be jeopardized-undue stresses can be imposed on steam turbine blades. For an industrial system the underfrequency load shedding may have to be resorted to on loss of a source, to restore load-generation balance and prevent Undervoltages in the distribution system. It is documented that as long as the utility source is connected, there may not be any significant change in the frequency. This is because the plant generators, which are relatively small, cannot dictate the system frequency when operating in synchronism. Undervoltage load shedding can be resorted to. In both case the stability and frequency recovery characteristics of the generators must be studied.