Technical Guide
Testing self-powered relays with SVERKER 900
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the “switch onto fault” situation, but it may happen when the circuit breaker is closed on an energized but
unloaded feeder.
This test aims to compare the operate time of the relay in two conditions:
1) Pre-fault of 500 mA present for 1 second, fault current of 8 A (above I>> threshold of 5A)
2) No pre-fault, fault current of 8 A (above I>> threshold of 5A)
It is enough to run 5 tests
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with the pre-fault current of 0,5 A (Figure 37) to get an idea of the operate time, then
set the pre-fault current to 0 A and run 5 tests again (Figure 38).
For repeating the tests, MTT in pre-fault and fault instrument has been used. Different approaches are of course
possible.
Figure 37. MTT Pre-fault and fault sequence for the presence of load before the fault and test results.
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“One shot is not enough”. Repeating the tests 5 times, gives an idea of the spread of the values, and helps to be
comfortable with the test results. We are evaluating the operate time! Note that we have not repeated the tests for the
inverse characteristics, as many shots are anyway generated. However, it could have been easily done, and we would have
seen a sort of distribution of time measurements around the mean value, probably near the theoretical value. In case of
doubts, use the statistical approach, especially if you need to report some doubtful performances.
