GE D90 Plus Instruction Manual page 216

GROUPED PROTECTION ELEMENTS
208
Figure 162: Neutral directional overcurrent configuration settings
The following settings are available for each neutral directional overcurrent element.
Function
Default: Enabled, Disabled
Default: Disabled
This setting enables and disables the neutral directional overcurrent protection element.
Source
Range: LINE (SRC 1), BKR 1 (SRC 2), BKR 2 (SRC 3)
Default: LINE (SRC 1)
This setting selects the signal source for the neutral directional overcurrent protection
element.
Polarizing
Range: Voltage, Current, Dual
Default: Voltage
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 neutral directional
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
the
Auxiliary VT Connection
zero-sequence voltage source (such as open delta connected secondary of VTs).
The zero-sequence (V_0) or auxiliary voltage (Vx), accordingly, must be higher than the
Voltage Cut-Off Level value to be validated for use 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 the neutral directional
The ground CT must be connected between the ground and neutral point of an
adequate local source of ground current. The ground current must be higher than
0.05 pu to be validated 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,
setting.
Source
setting is "Vn" and the auxiliary voltage is connected to a
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: PROTECTION
setting for polarization.
Source