GE 750 Instruction Manual page 358

PROTECTION SCHEMES
Note
NOTE
7 - 30
 Inject the preset current into the required number of phases and note the
delay time, then reset the timer.
 Repeat the last step four more times and obtain an average of the time
intervals.
 Reset the relay and disconnect the "Stop Trigger."
Phase IOC 2
The procedures to test this element are identical to those outlined for Phase IOC 1 above,
with the exception of the blocking from logic inputs check, which is performed as follows:
 Inject current into the required number of phases to cause a pickup.
 Assert a logic input to provide a "Block Phase Inst 2" and verify the
Pickup LED immediately turns off.
 Repeat last 2 steps for logic inputs "Block Phase O/C", "Block All O/C"
and "Block 1 TRIP Relay" as required.
Phase Directional OC
A plot of the operating characteristic of the phase directional feature for various settings of
MTA for Phase A is shown below. Other characteristics for specific MTA settings can be
deduced from this diagram. Note that the diagram is plotted for the phase current referred
to both the system phase-neutral voltage and the polarizing voltage used for Phase A (the
polarizing voltages for Phases B and C are Vca and Vab respectively).
270° 300° 330°
90°
60°
30°
0°
330°
300°
270°
180° 210° 240°
FIGURE 7–3: Phase Directional – Phase A Forward Operating Regions
The following descriptions present angles with reference to the polarizing 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.
For forward tripping and Wye connected VTs, use the test connections specified in FIGURE
7–1: Relay Test Wiring – Wye Connection on page 7–4 and use the following procedure:
 Set V
and 240°, respectively.
Ia LAGS Van PHASE VOLTAGE
0° 30° 60° 90°
270° 300° 330° 0°
Ia LAGS Vbc PHASE VOLTAGE
= PERMITTED TRIPPING REGION
= V = V >
MIN POLARIZING VOLTAGE
an bn cn
750 FEEDER MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 7: COMMISSIONING
120° 150° 180° 210° 240°
30° 60° 90° 120° 150°
setpoint at 0°, 120°,
270°
180°