GE L60 Instruction Manual page 320

5.5 GROUPED ELEMENTS
• 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
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 broken delta connected secondary of VTs).
The zero-sequence (V_0) or auxiliary voltage (V_X), accordingly, must be greater than the
setting specified in the
LEVEL
ing 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 greater 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. In
addition, the zero-sequence current (I_0) must be greater than the
CURRENT CUT-OFF LEVEL
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.
5
– 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").
• NEUTRAL DIR OC1 OP CURR: This setting indicates whether the 3I_0 current calculated from the phase currents, or
the ground current shall be used by this protection. This setting acts as a switch between the neutral and ground
modes of operation (67N and 67G). If set to "Calculated 3I0" the element uses the phase currents and applies the pos-
itive-sequence restraint; if set to "Measured IG" the element uses ground current supplied to the ground CT of the CT
bank configured as
setting must be "Voltage", as it is not possible to use the ground current as an operating and polarizing signal simulta-
neously. IG current has to be above 0.05 ps to be used as operate quantity.
• NEUTRAL DIR OC1 POS-SEQ RESTRAINT: This setting controls the amount of the positive-sequence restraint. Set
to 0.063 for backward compatibility with firmware revision 3.40 and older. Set to zero to remove the restraint. Set
higher if large system unbalances or poor CT performance are expected.
• NEUTRAL DIR OC1 OFFSET: This setting specifies the offset impedance used by this protection. The primary appli-
cation for the offset impedance is to guarantee correct identification of fault direction on series compensated lines. In
regular applications, the offset impedance ensures proper operation even if the zero-sequence voltage at the relaying
point is very small. If this is the intent, the offset impedance shall not be larger than the zero-sequence impedance of
the protected circuit. Practically, it shall be several times smaller. The offset impedance shall be entered in secondary
ohms.
See chapter 8 for additional details and chapter 9 for information on how to calculate this setting
• NEUTRAL DIR OC1 FWD ECA: This setting defines the characteristic angle (ECA) for the forward direction in the
"Voltage" polarizing mode. The "Current" polarizing mode uses a fixed ECA of 0°. The ECA in the reverse direction is
the angle set for the forward direction shifted by 180°.
• NEUTRAL DIR OC1 FWD LIMIT ANGLE: This setting defines a symmetrical (in both directions from the ECA) limit
angle for the forward direction.
5-192
is set to "Vn" and the auxiliary voltage is connected to a zero-sequence voltage
PRODUCT SETUP
for polarization. The ground CT must be connected between the ground and neutral
setting value.
. If this setting is "Measured IG", then the
NEUTRAL DIR OC1 SOURCE
L60 Line Phase Comparison System
NEUTRAL DIR OC1 SOURCE
SYSTEM SETUP
 menu to be validated for use as a polariz-
DISPLAY PROPERTIES
PRODUCT SETUP
5 SETTINGS
.
 
AC INPUTS VOLTAGE BANK
VOLTAGE CUTOFF
 
DISPLAY PROPERTIES
NEUTRAL DIR OC1 POLARIZING
GE Multilin