GE C70 Instruction Manual page 295

5 SETTINGS
Table 5–28: QUANTITIES FOR "MEASURED IG" CONFIGURATION
POLARIZING MODE DIRECTION
Voltage
1
-- - VAG (
where: V_0 VBG
= +
3
1 1
I_0 -- - IN -- - IA (
= = +
3 3
ECA = element characteristic angle and IG = ground current
When
NEUTRAL DIR OC1 POL VOLT
figure explains the usage of the voltage polarized directional unit of the element.
The figure below shows the voltage-polarized phase angle comparator characteristics for a phase A to ground fault, with:
• ECA = 90° (element characteristic angle = centerline of operating characteristic)
• FWD LA = 80° (forward limit angle = the ± angular limit with the ECA for operation)
• REV LA = 80° (reverse limit angle = the ± angular limit with the ECA for operation)
The above bias should be taken into account when using the neutral directional overcurrent element to directionalize other
protection elements.
REV Operating
Region
–ECA line
–3I_0 line
VCG
Figure 5–67: NEUTRAL DIRECTIONAL VOLTAGE-POLARIZED CHARACTERISTICS
• NEUTRAL DIR OC1 POLARIZING: This setting selects the polarizing mode for the directional unit.
– If "Voltage" polarizing is selected, the element uses the zero-sequence voltage angle for polarization. The user
can use either the zero-sequence voltage V_0 calculated from the phase voltages, or the zero-sequence voltage
supplied externally as the auxiliary voltage V_X, both from the
GE Multilin
DIRECTIONAL UNIT
COMPARED PHASORS
–V_0 + Z_offset × IG/3
Forward
–V_0 + Z_offset × IG/3
Reverse
)
VCG zero sequence voltage
+ =
IB IC ) zero sequence current
+ =
is set to "Measured VX", one-third of this voltage is used in place of V_0. The following
REV LA
–3V_0 line
line
LA
LA
REV LA
3V_0 line
line
C70 Capacitor Bank Protection and Control System
IG × 1∠ECA
–IG × 1∠ECA
,
,
FWD LA
line
VAG
(reference)
FWD Operating
LA
ECA
LA
VBG
FWD LA
line
NEUTRAL DIR OC1 SOURCE
5.6 GROUPED ELEMENTS
OVERCURRENT UNIT
I = |IG|
op
Region
3I_0 line
ECA line
827805A1.CDR
.
5-171
5