Underfrequency Protection of Power Systems for System Relief Load Shedding-System Splitting

1. It appears that regardless of the characteristics of an actual load, the dumping of appreciable overload on a generating station is likely to cause the frequency to drop too rapidly to permit manual switching to be effective, and automatic relays are necessary to prevent swamping of generators and to permit rapid restoration of even limited service. 2. Unnecessary line and generating station switching should be avoided. A combination of frequency and reverse power relays may be of assistance in reducing the probability of unnecessary switching, as the arrangement prevents breaker operation unless the load carried by the breaker is at least partially responsible for the underfrequency. 3. Selected loads may be dropped by frequency-sensitive relays. Loads that are likely to stall, causing damage to equipment such as ore crushers, rolling mills, etc., should be prevented from being recharged during the period of serious underfrequency. 4. An analysis is presented which permits consideration of both the normal and rotational power of both generators and loads. This may be useful in establishing settings for under frequency protection equipment.