Monitoring - GE 750 Instruction Manual

CHAPTER 7: COMMISSIONING
7.5.1 Current

Monitoring

7.5.2 Fault Locator
Note
NOTE
750 FEEDER MANAGEMENT RELAY – INSTRUCTION MANUAL
7.5 Monitoring
Phase Current Level
To test Phase Current monitoring, use the test connections specified in FIGURE 7–1: Relay
Test Wiring – Wye Connection or FIGURE 7–2: Relay Test Wiring – Delta Connection on page
7–5. The Indications and Operations are as outlined for Phase TOC 1 on page 7–25, except
that this element has no Trip function.
 Set the Delay time to 0.
 Inject current at a level below the pickup level into Phase A.
 Slowly increase the current until pickup is reached and the element
generates an output.
 Slowly reduce the current until the element resets, which should be 2%
of CT less than pickup when pickup
pickup > CT.
 Repeat Steps 2 to 4 for phase B and C current.
 Set the Delay timer to the required setting.
The following procedure checks the Phase Current Level Timing:
 Set the test source to a current at least 110% of pickup.
Turn off and reset the timer.
 Inject current into the relay and measure the time to operate.
 Repeat Step 2 four more times and obtain an average of the time
intervals
 Disconnect the Stop Trigger.
Neutral Current Level
To test Neutral Current monitoring, use the test connections specified in FIGURE 7–1: Relay
Test Wiring – Wye Connection or FIGURE 7–2: Relay Test Wiring – Delta Connection on page
7–5. The testing for this element is the same as outlined above for Phase Current Level,
except that current is the residual current injected into the phase current inputs.
To test the Fault Locator, use the test connections specified in FIGURE 7–1: Relay Test
Wiring – Wye Connection or FIGURE 7–2: Relay Test Wiring – Delta Connection on page 7–5.
Because of the broad range of variables that can be encountered in actual systems a
representative configuration with a set of impedances and instrument transformers have
been chosen to demonstrate these tests. The model used to calculate the voltage and
current phasors for the tests is a radial, 10 km long, three phase, four wire system of 13.8
kV nominal and 600 A feeder capacity. At the relay location there are wye-connected VTs
rated 14400/120 V and CTs rated 600/5 A. A prefault load of about 8.5 MVA exists on the
feeder. The relay is a 5 A unit.
MONITORING
≤
CT or 97 to 98% of pickup when
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