5.5 GROUPED ELEMENTS
The forward-looking function is designed to be more secure as compared to the reverse-looking function, and therefore,
should be used for the tripping direction. The reverse-looking function is designed to be faster as compared to the forward-
looking function and should be used for the blocking direction. This allows for better protection coordination.
The above bias should be taken into account when using the neutral directional overcurrent element to directionalize other
Figure 5–91: NEUTRAL DIRECTIONAL VOLTAGE-POLARIZED CHARACTERISTICS
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
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
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.
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
L60 Line Phase Comparison System
NEUTRAL DIR OC1 SOURCE
menu to be validated for use as a polariz-