Neutral Overcurrent - GE 750 Instruction Manual

Protection Schemes

Neutral Overcurrent

GE Multilin
3. Continue to increase the lagging angle until the alarm is again raised. The Phase
A current should be lagging the polarizing voltage by an angle of 270° ±2°.
4. Continue to increase the angle until the Phase A current is once again in phase
with the polarizing voltage. The alarm should remain.
5. Repeat the above Steps 1 through 4 for current angle adjusted in each of
Phases B and C.
a) Neutral TOC 1
The procedure to test this element is identical to that outlined in Phase TOC 1 on
page 7–18, except that current is injected into any one phase, and the element is
not subject to the "phases required for operation" and "voltage restrained time
overcurrent" tests.
The blocking from logic inputs check is different from that for Phase TOC 1 and is
performed as follows:
1. Inject current to cause a pickup.
2. Assert logic input to provide a "Block Neutral Time 1". The Pickup LED should
immediately turn off.
3. Repeat Steps 1 and 2 for logic inputs "Block Neutral O/C", "Block All O/C" and
"Block 1 Trip Relay" as required.
b) Neutral TOC 2
The procedure to test this element is identical to that outlined in Phase TOC 1 on
page 7–18, except that current is injected into any one phase, and the element is
not subject to the "phases required for operation" and "voltage restrained time
overcurrent" checks.
The blocking from logic inputs check is different from that for Phase TOC 1 and is
performed as follows:
1. Inject current to cause a pickup.
2. Assert logic input to provide a "Block Neutral Time 2". The Pickup LED should
immediately go out.
3. Repeat Steps 1 and 2 for logic inputs "Block Neutral O/C", "Block All O/C" and
"Block 1 Trip Relay" as required.
c) Neutral IOC 1
The procedure to test this element is identical to that outlined in Phase TOC 1 on
page 7–18, except that current is injected into any one phase, and the element is
not subject to the "phases required for operation", "linear reset timing", and
"voltage restrained time overcurrent" tests.
The blocking from logic inputs check is different from that for Phase TOC 1 and is
performed as follows:
1. Inject current to cause a pickup.
2. Assert a logic input to provide a "Block Neutral Inst 1". The Pickup LED should
immediately go out.
3. Repeat 1 and 2 for logic inputs "Block Neutral O/C", "Block All O/C" and "Block 1
Trip Relay" as required.
d) Neutral IOC 2
The procedure to test this element is identical to that outlined in Phase TOC 1 on
page 7–18, except that current is injected into any one phase, and the element is
not subject to the "phases required for operation", "linear reset timing", and
"voltage restrained time overcurrent" checks.
The blocking from logic inputs check is different from that for Phase TOC 1 and is
performed as follows:
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750/760
Feeder Management Relay
7–23