GE L30 Instruction Manual page 322

5.6 GROUPED ELEMENTS
Table 5–30: QUANTITIES FOR "MEASURED IG" CONFIGURATION
POLARIZING MODE
Voltage
1
-- - VAG (
where: V_0
=
3
1
I_0 -- - IN
= =
3
ECA = element characteristic angle
IG = ground current
Z_offset is the offset impedance, for which magnitude is the OFFSET setting and angle is the FWD ECA
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
5 protection elements.
Figure 5–71: 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
5-182
DIRECTIONAL UNIT
DIRECTION
–V_0 + Z_offset × IG/3
Forward
–V_0 + Z_offset × IG/3
Reverse
)
VBG VCG zero sequence voltage
+ + =
1
-- - IA ( IB IC ) zero sequence current
+ + =
3
is set to "Measured VX", one-third of this voltage is used in place of V_0. The following
REV LA
line
REV Operating
Region
LA
–ECA line
–3I_0 line
VCG
LA
REV LA
line
L30 Line Current Differential System
COMPARED PHASORS
IG × 1∠ECA
–IG × 1∠ECA
,
,
FWD LA
–3V_0 line
line
VAG
(reference)
LA
ECA
LA
FWD LA
line
3V_0 line
NEUTRAL DIR OC1 SOURCE
5 SETTINGS
OVERCURRENT UNIT
I = |IG|
op
FWD Operating
Region
3I_0 line
ECA line
VBG
827805A1.CDR
.
GE Multilin