10.6
SEL-749M Relay Instruction Manual Date Code 20080918
Testing and Troubleshooting
Commissioning Tests
Make sure that each contact closure does what you
want it to do in the annunciation, control, or trip circuit
associated with that contact closure.
Step 19. Perform any desired protection element tests. Perform only
enough tests to prove that the relay operates as intended;
exhaustive element performance testing is not necessary for
commissioning.
Step 20. Connect the relay for tripping duty.
Step 21. Verify that any settings changed during the tests performed in
Step 18 and Step 19 are changed back to the correct values for
your application.
Step 22. Use the serial port commands in Table 10.2 to clear the relay
data buffers and prepare the relay for operation.
This prevents data generated during commissioning testing
from being confused with operational data collected later.
Step 23. When it is safe to do so, start the motor.
Step 24. Verify the following ac quantities by using the front-panel
METER or serial port METER command.
➢ Phase current magnitudes should be nearly equal.
➢ Phase current angles should be balanced, have proper
phase rotation, and have the appropriate phase
relationship to the phase voltages.
Step 25. If your relay is equipped with voltage inputs, check the
following:
➢ Phase voltage magnitudes should be nearly equal.
➢ Phase voltage phase angles should be balanced and
have proper phase rotation.
The SEL-749M is now ready for continuous service.
Functional Tests
Phase Current Measuring Accuracy
Step 1. Connect the current source to the relay, as shown in
Figure 10.4.
Step 2. Using the front-panel or the serial port SHOW command,
record the CTR1 and PHROT setting values.
Step 3. Set the phase current angles to apply balanced three-phase
currents in accordance with the PHROT setting. Refer to
Figure 10.2.
Table 10.2 Serial Port Commands That Clear Relay Data Buffers
Serial Port
Command
Ta s k Per fo r m e d
MOT R Clears Motor Statistics buffers.
SUM R Resets Event Report and Summary Command buffers.
SER R Resets Sequential Events Record buffer.
Courtesy of NationalSwitchgear.com
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