8.8
SEL-551 Relay Instruction Manual Date Code 20110408
Testing and Troubleshooting
Acceptance Testing
b. Apply the appropriate control voltage to each input and
make sure the corresponding target LED turns on.
Note that the control voltage required to assert an input
is jumper selectable.
If you suspect the jumpers to be different from the
factory default, refer to Section 2: Installation for the
jumper locations.
Metering
Step 1. Purpose:
Connect simulated power system secondary current sources to
the relay.
Method:
a. Turn power off to the relay and connect current sources.
If three current sources are available, connect them to
the relay as shown in Figure 8.3. If only two current
sources are available, connect the sources as shown in
Figure 8.4 to generate balanced positive-sequence
currents.
b. Set the current sources to deliver 1 A secondary.
c. Set the current angles (e.g., B-phase lags A-phase by
120°) according to the phase rotation setting PHROT
(i.e., PHROT = ABC or ACB).
Step 2. Purpose:
Verify correct current levels.
Method:
a. Turn relay power on, and use the METER command to
display the currents applied in Step 1.
With applied currents of 1 A secondary per phase and a
current transformer ratio of 120:1 (assuming setting
CTR = 120), the displayed line currents should be close
to 120 amperes primary.
Step 3. Purpose:
Verify phase rotation.
Method:
a. Verify that residual (IG) and negative-sequence (3I2)
quantities are approximately zero (or much less than the
approximately 120 A primary displayed for the phases).
If IG equals approximately 3 times the applied current,
then all three phases have the same angle. If 3I2 equals
approximately 3 times the applied current, then the
phase rotation is reversed.
b. Turn the current sources off.
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