Date Code 20000421 Maintenance and Testing 7-3
SEL-251, -2, -3 Instruction Manual
Testing Via Target LED Illumination
During testing you can use target lamp illumination to determine relay element status. Using the
TARGET command, set the front panel targets to display the element under test. For example,
the overcurrent element pickups appear in Relay Word row 1. When you type the command
TARGET 1 <ENTER>, the LEDs display the status of the elements in Relay Word row 1.
Thus, with Target 1 displayed, if the phase time-overcurrent element pickup (51P) asserts, the
left most LED illuminates. Using LED illumination as an indicator, you can measure the element
operating characteristics.
When the TARGET command sets target LED output to a level other than 0 (Relay Targets), the
front panel target markings no longer correspond to illuminated LEDs and the LEDs do not latch.
If you place the relay in service with a target level other than Level 0, it automatically returns to
Level 0 when an automatic message transmits to a timed out port. While this feature prevents
confusion among station operators and readers, it can be inconvenient if the relay tester does not
want targets to revert to Level 0.
To simplify testing using targets, set the relay AUTO setting equal to the port which you intend
to use. Also, set that port TIME setting equal to zero. This prevents automatic message
transmission to a port which may be timed out. Remember to reset these settings and the target
level before returning the relay to service following tests.
Testing Via Output Contact Assertion
To test using this method, set one programmable output contact to assert when the element under
test picks up. With the SET n p command, set an output contact equal to the element under test.
For an "a" contact, when the condition asserts, the output contact closes; when the condition
deasserts, the output contact opens.
For a "b" contact, when the condition asserts, the output contact opens. When the condition
deasserts, the output contact closes. With the Conventional Terminal Block model the program-
mable contacts can be specified at the factory as "a" or "b." Using contact operation as an
indicator, you can measure element operating characteristics, stop timers, etc.
Tests in this section use the output contact method and assume an "a" output contact.
Using a Breaker Simulator
Because much of the relay logic depends on whether the breaker is open or closed, it is important
to use a breaker simulator. The following logic depends on the state of the circuit breaker status
input:
• Reclosing Relay Logic
• Close Function Logic
• Trip Circuit Monitor Logic
• 52AT and 52BT Functions
• Circuit Breaker Monitor Logic
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