5.5 GROUPED ELEMENTS
Figure 5–44: NEUTRAL DIRECTIONAL VOLTAGE-POLARIZED CHARACTERISTICS
The above figure shows the voltage-polarized phase angle comparator characteristics for a phase-A to ground fault, with:
= 90° (Element Characteristic Angle = centerline of operating characteristic)
= 80° (Forward Limit Angle = the ± angular limit with the ECA for operation)
= 80° (Reverse Limit Angle = the ± angular limit with the ECA for operation)
The element incorporates a current reversal logic: if the reverse direction is indicated for at least 1.25 of a power system
cycle, the prospective forward indication will be delayed by 1.5 of a power system cycle. The element is designed to emu-
late an electromechanical directional device. Larger operating and polarizing signals will result in faster directional discrimi-
nation bringing more security to the element operation.
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 protection elements.
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 Vx, both from the
The calculated V_0 can be used as polarizing voltage only if the voltage transformers are connected in Wye. The aux-
iliary voltage can be used as the polarizing voltage provided
ILIARY VT CONNECTION
open delta connected secondary of VTs).
The zero-sequence voltage (V_0) or auxiliary voltage (Vx), accordingly, must be higher than 1 V secondary to be vali-
dated for use as a polarizing signal. If the polarizing signal is not valid, 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
and neutral point of an adequate local source of ground current. The ground current must be higher than 0.05 pu to be
is set to "Vn" and the auxiliary voltage is connected to a zero-sequence voltage source (such as
for polarization. The ground current transformer must be connected between the ground
L90 Line Differential Relay
NEUTRAL DIR OC1 SOURCE
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