GE T60 Instruction Manual page 444

GROUPED ELEMENTS
5
NEUTRAL DIR OC1 POLARIZING
• 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
(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
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
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. In addition, the
zero-sequence current (I_0) must be greater than the
setting value.
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, ensure that a reversal of the ground current does not occur for a high-side fault. Assume that the
low-side system impedance is minimal when checking for this condition. A similar situation arises for a wye/delta/wye
transformer, where current in one transformer winding neutral can reverse when faults on both sides of the
transformer are considered.
5-262
Figure 5-146: Neutral directional voltage-polarized characteristics
— This setting selects the polarizing mode for the directional unit.
is set to "Vn" and the auxiliary voltage is connected to a zero-sequence voltage source
PRODUCT SETUP  DISPLAY PROPERTIES
for polarization. The ground CT must be connected between the ground and neutral point
.
NEUTRAL DIR OC1 SOURCE
SYSTEM SETUP  AC INPUTS  VOLTAGE BANK 
menu to be validated for use as a polarizing signal. If
PRODUCT SETUP  DISPLAY PROPERTIES  CURRENT CUT-OFF
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
VOLTAGE CUTOFF LEVEL