GE t60 Instruction Manual page 174

5.5 GROUPED ELEMENTS
Figure 5–51: NEUTRAL DIRECTIONAL VOLTAGE-POLARIZED CHARACTERISTICS
• NEUTRAL DIR OC1 POLARIZING: This setting selects the polarizing mode for the directional unit.
5
– 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").
• 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
5-96
REV LA
line
REV Operating
Region
LA
–ECA line
–3I_0 line
VCG
LA
REV LA
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
. Naturally, it is not possible to use the ground current as an operating
NEUTRAL DIR OC1 SOURCE
T60 Transformer Management Relay
FWD LA
–3V_0 line
line
VAG
(reference)
FWD Operating
LA
ECA
LA
VBG
FWD LA
line
3V_0 line
NEUTRAL DIR OC1 SOURCE
SYSTEM SETUP
5 SETTINGS
Region
3I_0 line
ECA line
827805A1.CDR
.
AC INPUTS VOLTAGE BANK
GE Multilin