ABB RELION REX640 Technical Manual page 880

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Protection functions

Conversion from element start to monitored data signals

Start of element

1) This applies to near three-phase faults. If voltages are still relatively high, all PP releases are given,

depending on the impedances seen inside the GFC zone.

2) This applies to near three-phase faults with EF indication. If voltages are still relatively high, all or some

PE and PP releases (except ABC Fault) are given, depending on the impedances seen inside the GFC

In case of a high-impedance earthed network, a phase preference logic can be added

to complement the phase selection in case of a cross-country fault. This can affect the

RELEASE_PE signals.

In case of a low-impedance earthed network, a faulted loop selection logic can be

added to complement the phase selection in case of a two-phase-to-earth fault. This

can affect the RELEASE_PE and RELEASE_PP monitored data signals.

Cross-country fault detection function for high-impedance earthed

In isolated and high-impedance earthed networks, the overvoltages produced by a

single-phase earth fault may lead to a cross-country fault, where two simultaneous

single-phase earth faults are present in the system but in different locations and

phases. The cross-country fault is hazardous because the magnitude of the fault

current through earth can be as high as in the case of a two-phase short circuit fault.

The protection must therefore remove the cross-country fault quickly without

sacrificing the selectivity. This can be done with a phase preference logic which is

activated by the cross-country fault detection function. The phase preference logic

1MRS759142 C

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