KUC755AE105 3BHB005243R0105 ABB Control DCS system module to stabilize inventory
KUC755AE105 3BHB005243R0105 ABB Control DCS system module to stabilize inventory

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The undervoltage protection based on calculated positive phase-sequence voltage

can be applied to disconnecting a smaller power plant from the outside network, for

instance in situations where there is a fault in the network which can be critical for

the power plant, such as a short circuit either at the transmission or distribution

network level.

A situation of this kind can be critical for different reasons. The power plant can be

left to feed an isolated network due to a trip caused by a fault. In this case, there is a

risk that the isolated network, which is in asynchronous state compared to the rest of

the network, is reconnected to the network as a result of an autoreclosure, for

instance. In addition, the power plant can also fall into an asynchronous state in a

fault situation. These critical situations can be prevented by disconnecting the power

plant from the network fast enough by tripping the connecting circuit breaker.

The benefit of this function is that the voltage value measured during or after a

network fault is a good measure of how critical the fault is for a smaller power plant.

When the positive phase-sequence voltage value falls below the critical limit, the

power plant has to be disconnected from the network.

REU610 measuring the positive phase-sequence voltage complements other

methods used to disconnect smaller power plants. The application of these methods

is based on frequency and voltage measurement. The undervoltage protection based

on calculated positive phase-sequence voltage requires that the relay is in threephase use.