GE 750 Instruction Manual page 361

CHAPTER 7: COMMISSIONING
Note
NOTE
750 FEEDER MANAGEMENT RELAY – INSTRUCTION MANUAL
Neutral IOC 2
The procedure to test this element is identical to that outlined in Phase TOC 1 on page 7–
25, 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:
 Inject current to cause a pickup.
 Assert a logic input to provide a "Block Neutral Inst 2".
The Pickup LED should immediately go out.
 Repeat last 2 steps for logic inputs "Block Neutral O/C", "Block All O/
C" and "Block 1 Trip Relay" as required.
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.
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:
 Set V
Set a current of 0.2 of nominal to lag V
direction) and inject into Phase A. Note that –V
POLARIZING VOLTAGE
 Reduce V
Residual Current Lags Faulted Phase Voltage
30° 90° 150° 210° 270°
= PERMITTED TRIPPING REGION
= V = V = nominal voltage at 0°, 120°, and 240° respectively.
an bn cn
.
until –V is greater than the
an 0
PROTECTION SCHEMES
330° 30° 90°
by 180° (in the tripping
an
is less than the
MIN
0
MIN POLARIZING VOLTAGE
.
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