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Load Shedding - By Frequency Relay

The Load Shedding function provides under-frequency protection at the main distribution substation. As system frequency decreases, load is disconnected in discrete steps according to frequency thresholds. Protective relays are used for automatic gradually under-frequency load shedding. Under and over-frequency relays are specified by frequency settings and delays. The frequency must remain above/below the specified frequency for the specified delay for the relay to operate. Zero delays are permitted. This procedure describes what activities are performed by an operator after the function load shedding by frequency opened a corresponding set of circuit breakers which resulted in the loads being disconnected from the power system. When the emergency situation is over, the operator has to restore the power. Load Shedding (by order) is described in [UC27]. It is possible to create and execute certain jobs in order to restore power [UC24], [UC25] and [UC26].

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