GE 750 Instruction Manual page 278

750/760
Feeder Management Relay
NOTE
7–24
1. Inject current to cause a pickup.
2. Assert a logic input to provide a "Block Neutral Inst 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.
e) Neutral Directional OC
If dual polarizing is required, check the operation of the voltage and current
polarized elements individually as outlined below, then check the overall dual
polarized response as outlined at the end of this section.
A plot of the operating characteristic of the voltage polarized neutral directional
feature for various settings of MTA is shown below. Other characteristics for specific
MTA settings can be deduced from this diagram. Note that the diagram is plotted for
the residual current referred to the system faulted-phase phase-to-neutral voltage.
30°
0°
60°
120°
180°
240°
300°
FIGURE 7–4: Neutral Directional Voltage Polarized Fwd Operating Regions
The following descriptions present angles with reference to the faulted
phase voltage and assume an MTA setting of 180°. For an MTA setting other
than 180° alter the noted angles to those established by the programmed
MTA.
To test forward tripping with voltage polarization, use the test connections specified
in FIGURE 7–1: Relay Test Wiring – Wye Connection on page 7–4 and follow the
procedure below:
1. Set V = V = V = nominal voltage at 0°, 120°, and 240° respectively. Set a
an bn cn
current of 0.2 of nominal to lag V
into Phase A. Note that –V
2. Reduce V until –V is greater than the
an 0
3. Slowly increase the angle of the Phase A current in the lagging direction. At an
angle lagging Van by 270° ±2°, any output relays programmed for this
condition should operate if the function is set to "Control". If the function is set
to "Alarm", check that the Alarm and Message LEDs are flashing, the Neutral
Directional Reverse alarm message is displayed, and any output relays
programmed for this condition are operated.
4. Continue to increase the lagging angle through 0°, until the block message
disappears at an angle lagging V
5. If desired, repeat the above Steps 1 through 4 for Phases B and C using I
faulted phase voltage V
To test forward tripping with current polarization, use the test connections specified
and procedure specified below:
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Residual Current Lags Faulted Phase Voltage
90° 150° 210° 270° 330°
= PERMITTED TRIPPING REGION
by 180° (in the tripping direction) and inject
an
is less than the
MIN POLARIZING VOLTAGE
0
MIN POLARIZING VOLTAGE
by 90° ±2°. Turn the current off.
an
and I with faulted phase voltage V
bn c
Protection Schemes
30° 90°
.
.
with
b
.
cn
GE Multilin