GE D90 Plus Instruction Manual page 260

GROUPED PROTECTION ELEMENTS
250
Figure 214: 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 greater than the
Voltage Cutoff Level of the general voltage inputs (found under the Protection > Power
System > AC Inputs - Voltage settings) to be validated for use as a polarizing signal. If
the polarizing signal is invalid, neither forward nor reverse indication is given. In addition,
the zero-sequence current (I_0) must be greater than the
value specified in the Protection > Power System > AC Inputs – Current menu.
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 greater 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.
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
Current Cutoff Level
Source setting for polarization.