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Date Code 20000421
Maintenance and Testing
7-1
SEL-251, -2, -3 Instruction Manual
SECTION 7: MAINTENANCE AND TESTING
T
EST
P
ROCEDURES
Test Aids Provided by the Relay
The following features assist you during relay testing and calibration:
METER
Command
The METER command shows the voltages and currents presented to the
relay in primary values. The relay calculates megawatts (MW) and
megavars (MVAR) from these voltages and currents. These quantities are
useful for comparing relay calibration against other meters of known
accuracy.
When testing the relay, first verify relay calibration. Consider all tests
invalid if you determine that the relay is out of calibration. Each relay is
calibrated at the factory prior to shipment and should not require further
adjustment. If calibration is necessary, refer to
Calibration
in this section.
TARGET
Command
The relay allows you to reassign front panel targets to indicate elements and
intermediate logic results in the Relay Word as well as input and output
contact status. Use the TARGET command to reassign the front panel
LEDs. Once target LEDs are reassigned from the default targets, the front
panel targets are no longer latching. This means the targets follow the
pickup and dropout condition in much the same manner as an output
contact. See
Section 3: Communications
for more information about the
TARGET command.
By employing the target LEDs for testing, you need not change the relay
settings for testing purposes.
Event Reporting
The relay generates an eleven-cycle event report in response to a trip
condition or other user selected conditions. Each event report contains
voltage and current information, relay element states, and input/output
contact information in quarter-cycle resolution. If you question the relay
response or your test method, use the event report for assistance.
Each event report is date and time tagged relative to the 16th quarter-cycle
of the event report. Each report is triggered upon assertion of designated
relay elements and/or contact inputs and outputs. If the timeout of a
protective element results in TRIP output contact closure, the trip generates
a second event report. Thus, the relay generates two event reports: the first
when the designated instantaneous element asserts, the second when the
TRIP output contact closes. Where time delayed pickup (TDPU) timers are
concerned, use the event report time tag to determine the validity of a TDPU
timer setting. Simply subtract the latest event report time tag from the
previous event report time tag.
Section 2: Specifications
has further details
concerning event report generation.