GE 750, Instruction Manual

Page: 436 / 504

17-
30
750/760 Feeder Management Relay GE Power Management
17.7 PROTECTION SCHEMES 17 COMMISSIONING
17
c) FORWARD TRIPPING WITH DUAL POLARIZATION
Test Connections per Figure 17–5: NEUTRAL DIRECTIONAL TEST CONNECTION WITH POLARIZING
CURRENT.
As operations of each neutral directional sensing element have been checked under voltage and current polar-
ization, it is only necessary to check that both directional elements are operational, and that either element can
block tripping for reverse faults.
1. Set V
an
to 60%, and V
bn
= V
cn
to 100% nominal voltage at phase angles of 0
°
, 120
°
, and 240
°
, respec-
tively.
2. Inject a current of 0.2 x nominal into the phase current input of the relay (3 I
o
) at an angle outside the trip-
ping region of the set MTA, as compared to faulted phase voltage V
an
. The Neutral Directional Reverse
alarm should appear.
3. Inject a current of 0.2 x nominal, lagging the 3 I
o
current by 180
°
, into the ground current input. The block
alarm should remain.
4. Increase the angle of the ground current lagging 3 I
o
current through a complete 360
°
rotation back to the
original angle of lagging by 180
°
. The block alarm should remain throughout the rotation as the voltage
polarized element is still blocking.
5. Maintaining the ground current angle lagging 3 I
o
by 180
°
increase the angle of 3 I
o
lagging the V
an
voltage
through a complete 360
°
rotation back to the original angle. The block alarm should remain throughout the
rotation as the current polarized element is still blocking.
6. Increase the angle of the ground current lagging 3 I
o
current until the currents are in-phase. The block alarm
should remain.
7. Maintaining the ground current angle in-phase with 3 I
o
increase the angle of 3 I
o
lagging the V
an
voltage
until into the permitted region. The block alarm should disappear when the angle reaches the tripping
region.
17.7.13 GROUND TIME OVERCURRENT
The procedure to test this element is identical to that outlined for Section 17.7.3: PHASE TIME OVERCUR-
RENT 1 on page 17–21, with the following exceptions.
Current is injected into the ground input terminals, and the element is not subject to the "phases required for
operation" and “voltage restrained time overcurrent” tests.
Blocking From Logic Inputs
1. Inject current to cause a pickup.
2. Assert a logic input to provide a "Block Ground Time". The PICKUP indicator should immediately go out.
3. Repeat steps 1 and 2 for logic inputs "Block Ground O/C", "Block All O/C" and “Block 1 TRIP Relay” as
required.