ABB RELION REX640 Technical Manual page 872

Section 4
Protection functions
866
Min phase angle GFC
Max phase angle GFC
GUID-41EFE5E8-E6CA-47E7-877E-6F4952B6F155 V2 EN
Figure 468: Characteristic of the directional function for earth faults
The Chr angle GFC setting, also known as relay characteristic angle or basic angle, is
used to turn the directional characteristic. It has a positive value when the operating
quantity lags the polarizing quantity and a negative value when the operating quantity
leads the polarizing quantity. For low-impedance earthed networks, Chr angle GFC
equals the angle of the fault loop impedance and is typically positive.
The Min phase angle GFC and Max phase angle GFC settings define the width of the
operating sector. These settings are mirror-symmetric to the origin for reverse
(backward).
The directional function for earth faults must operate at fault current values below the
magnitude of the load currents. The use of sequence quantities is preferred for
polarizing quantity as phase quantities are affected by the load currents. Four
possibilities are available and defined by the Pol quantity GFC setting.
Table 829: Polarizing quantities for optional directional function for earth faults in low-impedance
earthed networks
Pol quantity GFC Polarizing quantity
Zero seq. volt. -U
Neg. seq. volt. -U
Zero seq. cur. I
oref
Zro vol.OR cur. -U
Pol. quantity
Chr angle GFC = +45 deg.
Min phase angle GFC
Operating quantity
I
0 0
I
2 2
I
0
OR I I
0 oref 0
1MRS759142 C
maximum torque line
Max phase angle GFC
Description
Zero-sequence voltage
polarization
Negative-sequence
voltage polarization
Zero-sequence current
polarization
Dual polarization
REX640
Technical Manual