ABB RELION 620 Series Technical Manual page 498

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Protection functions

Angle load area GFC

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Circular (mho) characteristics with load discrimination logic enabled

Before releasing the phase-to-phase or three-phase fault measuring impedance elements

of zones, the measured load impedance is evaluated with the load discrimination logic. If

the load impedance is detected inside the sector reserved for load impedance, the zone

release is blocked. The activation of the load discrimination requires all phase-to-phase

voltages to exceed the Load Dsr Ena V GFC setting. The activation of the load

discrimination logic is indicated by the LODDSR_GFC output signal.

Impedance measurement

21P provides three independent phase-to-phase measuring elements per zone and the

three-phase fault is measured with a dedicated measurement element.

Impedance measurement module measures the impedance of a particular faulty loop when

GFC module releases the loop. The measurement is based on the full-cycle DFT-filtered

current and voltage phasors. This gives a typical operating time of less than two cycles.

21P operation is based on the impedance-mapping approach, where the fault loop

impedance is calculated and compared to the zone boundaries. If the impedance is

recognized inside the operation zone, the corresponding trip output TRIP_Zx (x = 1...5)

is activated after the Time delay Znx, x = 1...5 setting is elapsed.

The calculated fault loop impedance of zone 1 can be read from the FLTLOOP_RPP and

FLTLOOP_XPP settings in the monitored data. It can also be seen in the fault record.

Phase-to-phase impedance measurement

The phase-to-phase impedance measurement for a particular loop is performed on the

receipt of the phase-to-phase release signal from the GFC module. Phase-to-phase

Ris reach load GFC

1MAC504801-IB E

Angle load area GFC

620 series ANSI

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