GE LPS-D, Instruction Manual, Page: 78 / 436

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LPS-D Line Protection System GE Power Management
2.3 PROTECTION SETTINGS 2 CALCULATION OF SETTINGS
2
108: Z1GROUNDK0 - Z1GROUND Zero Sequence Compensation Factor
Z1GROUNDK0 determines the amount of zero-sequence current used in the Zone 1 ground-distance func-
tions to provide “self-compensation.” This permits the reach setting to be based on the positive-sequence
impedance to a ground fault. It should be set to the following:
Z1GROUNDK0 =
where: = zero-sequence impedance of line
= positive-sequence impedance of line
109, 110: NOT USED
111: Z1GCHARANG - Zone 1 Ground Characteristic Timer Angle (Revision B models only)
Z1GCHARANG can be set from 80 to 155° in increments of 1°. This setting determines the “tilt” of the reac-
tance portion of the quadrilateral ground distance characteristic.
A ground distance function employing a reactance/quadrilateral characteristic provides excellent protection on
a homogeneous system where the fault current at the relay location is essentially in phase with the total fault
current for a single line to ground fault at the remote end of the line (or if the fault current at the relay location is
more lagging than the total fault current for a single line to ground fault at the remote end of the line). On a non-
homogeneous system where the fault current at the relay location is more leading than the total fault current for
a single line to ground fault at the remote end of the line, a conventional reactance/quadrilateral characteristic
will tend to overreach, especially when fault resistance is present. In this situation, the “tent” characteristic
shown below should be used.
Figure 2–3: TENT CHARACTERISTIC
112: Z1RGREACH - Zone 1 Resistive Ground Reach (Revision B models only)
Z1RGREACH can be set from 0.01 to 100.00
Ω
for a 5 A rated relay (0.05 to 500
Ω
for a 1 A rated relay). It
determines the position of the right resistive blinder for the ground distance quadrilateral characteristic to pro-
vide coverage for resistive ground faults. If Zone 2 is also set to Quad mode, this setting should be calculated
as 0.8 or less of the Zone 2 Resistive Ground Reach (Protection Setting 211: Z2RGREACH). If Zone 2 is not
set to Quad mode, the setting should be calculated at 0.8 (if “tent” characteristics are used) or less (0.6 to 0.7 if
“tent” characterstics are not used) of the positive-sequence resistance seen by the relay under maximum load
conditions and unity power factor. Also, to maintain zone accuracy, it is recommended that the resistive reach
is not greater than 10 times the Ground Distance Reach (Protection Setting 105: Z1GRDREACH) for this zone.
0.95 Z
0 L
Z
1 L
⁄ ( ) ×
Z
0 L
Z
1 L
R
X
1
3
2
4
“TENT” CHARACTERISTIC
TENTCHAR.CDR