ABB RELION REX640 Technical Manual page 951

Protection and control

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1MRS759142 F

Start of element

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 signals.

Faulted phase selection, the voltage-dependent overcurrent method

The "Voltdep overcur" method combines the overcurrent and undervoltage

conditions. The phase current amplitude is compared to the

threshold setting but a lower current

an undervoltage condition. This increases the sensitivity of the fault detection. The

amplitude of phase-to-earth and phase-to-phase voltages is compared to the

Ph Sel GFC and PP V Ph Sel GFC settings. In case of a three-phase fault, the phase-

to-phase voltages are monitored and compared to the

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

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

and PP releases (except ABC Fault) are given.

Technical Manual

Earth-fault recognition is always required to release a phase-to-earth

impedance-measuring element.

Lo A Ph Sel GFC threshold is valid during

PP V Ph Sel GFC setting.

Protection functions

Str A Ph Sel GFC