GE L60 Instruction Manual page 223

5 SETTINGS
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 5–74: 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 Vx, both from the
The calculated V_0 can be used as polarizing voltage only if the voltage transformers are connected in Wye. The
auxiliary voltage can be used as the polarizing voltage provided
AUXILIARY VT CONNECTION
source (such as open delta connected secondary of VTs).
The zero-sequence (V_0) or auxiliary voltage (Vx), accordingly, must be higher than 0.02 pu nominal voltage to be
validated as a polarizing signal. If the polarizing signal is invalid, neither forward nor reverse indication is given.
– If "Current" polarizing is selected, the element uses the ground current angle connected externally and configured
under
NEUTRAL OC1 SOURCE
point of an adequate local source of ground current. The ground current must be higher than 0.05 pu to be vali-
dated as a polarizing signal. If the polarizing signal is not valid, neither forward nor reverse indication is given.
For a choice of current polarizing, it is recommended that the polarizing signal be analyzed to ensure that a known
direction is maintained irrespective of the fault location. For example, if using an autotransformer neutral current
as a polarizing source, it should be ensured that a reversal of the ground current does not occur for a high-side
fault. The low-side system impedance should be assumed minimal when checking for this condition. A similar sit-
uation arises for a Wye/Delta/Wye transformer, where current in one transformer winding neutral may reverse
when faults on both sides of the transformer are considered.
– If "Dual" polarizing is selected, the element performs both directional comparisons as described above. A given
direction is confirmed if either voltage or current comparators indicate so. If a conflicting (simultaneous forward
and reverse) indication occurs, the forward direction overrides the reverse direction.
• NEUTRAL DIR OC1 POL VOLT: Selects the polarizing voltage used by the directional unit when "Voltage" or "Dual"
polarizing mode is set. The polarizing voltage can be programmed to be either the zero-sequence voltage calculated
from the phase voltages ("Calculated V0") or supplied externally as an auxiliary voltage ("Measured VX").
GE Multilin
REV LA
–3V_0 line
line
VAG
(reference)
LA
ECA
LA
FWD LA
REV LA
3V_0 line
line
is set to "Vn" and the auxiliary voltage is connected to a zero-sequence voltage
for polarization. The Ground CT must be connected between the ground and neutral
L60 Line Phase Comparison Relay
5.5 GROUPED ELEMENTS
FWD LA
line
FWD Operating
Region
LA
3I_0 line
ECA line
LA
VBG
line
827805A1.CDR
.
NEUTRAL DIR OC1 SOURCE
SYSTEM SETUP AC INPUTS
5
VOLTAGE BANK
5-131