ABB RELION REX640 Technical Manual page 871

1MRS759142 C
REX640
Technical Manual
3I /I
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Gnd Op current 2 GFC
Gnd Op current GFC
GUID-7404A72D-C37B-4480-9829-8166C3C48167 V2 EN
Figure 467: Stabilized residual current measurement for earth-fault detection
The residual voltage can also be used as a complementary criterion for earth-fault
detection. This is valid when the setting EF detection Mod GFC is "Io OR Uo" or EF
detection Mod GFC is "Io AND Uo". The threshold setting for the residual voltage is
Gnd Str voltage GFC.
Directional function for earth faults
In low-impedance earthed networks, when the System grounding GFC setting is set to
"Low impedance", the earth-fault detection function can be optionally supervised by
a directional function which can be enabled with the Dir mode EF GFC setting. If Dir
mode EF GFC is set to "Forward" or "Reverse", the earth-fault direction is also
detected. The calculated direction for the earth fault is indicated in the DIR_E_FLT
monitored data ("unknown", "forward", "backward" (reverse), "both"). Direction
criteria do not directly affect earth-fault detection, but the earth-fault direction
information is used for zone starting, when only those directional zones that are set to
the indicated earth-fault direction can be started.
The operation characteristic of the directional function is defined by three settings:
Chr angle GFC, Min phase angle GFC and Max phase angle GFC.
Stab slope 2 GFC
Stab slope 1 GFC
Blocking due
to CT errors
1.0
A Ph Stab value GFC
Section 4
Protection functions
Blocking
due to CT
saturation
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