Digital inputs and outputs are failure points in modern relaying that cannot be tested via the relay’s self-tests. An output contact can be fused closed or be frozen open. We can test the outputs by pulsing the relay contacts to make sure that they change state.
Digital inputs are often damaged by incorrect connections, so it is important to use as much of the installed wiring as we can. Always try to operate the end-device connected to a relay whenever possible. Applying your own circuit to test in-service inputs should be a last resort.
It is important that we test all the inputs and outputs during an acceptance test to prove that the manufacturer sent us a functioning relay. Better to find out now that there is a problem, instead of later when the relay is in service.
Watch these videos to see how to test the digital inputs and outputs of protective relays from these manufacturers:
Schweitzer Engineering Laboratories, Inc.
Beckwith Electric Co., Inc.
General Electric / Multilin
Don’t see your relay in this series? Leave a comment below and we’ll see if we can get a demonstration unit and add a video for that test-set.
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