Testing Recloser Logic: More Than Just “Did It Close?”
Once a recloser logic failed on a 33kV line during a storm. First trip was good. Second trip was good. Then it tried to reclose into a still-faulted line — and didn’t lock out.
You know what happened next.
Recloser that did not operate properly
And on the photo above you can see a result of a battle between a an advanced technology and… a squirrel.
Winfall Substation lost power due to equipment failure. A squirrel caused a fault on a down-line transformer, and a recloser that was supposed to disconnect power to the transformer failed to operate. The transformer and the recloser quickly overheated and were destroyed in electrical fires
So yeah, let’s talk about testing autoreclose functions — because it’s one of the most misunderstood, most under-tested parts of modern protection.
What’s usually tested?
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Inject fault current, make sure the relay trips.
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Wait X seconds, check that it recloses.
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Inject fault again, check second trip and final lockout.
Cool. That’s about 30% of what you should be doing.
What’s usually missed?
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Dead time coordination: Is it giving the line enough time to deionize, or are you reclosing into an arc?
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Reclose blocking under live bus: Is the relay smart enough to not reclose when bus voltage is present? It should be.
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Conditional reclosing: Some schemes only allow reclose under specific conditions (like voltage recovery). You testing that?
And if you’re using IEC 61850, guess what: reclose logic is often in the logic blocks, not the protection element. If you’re only injecting current, you’re not even touching the logic paths that matter.
How do we test it properly?
You have to simulate the entire sequence:
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Inject fault current — relay trips.
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Drop voltage to simulate dead line.
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Inject zero current + 0V for dead time — check that reclose command is issued.
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Inject fault again — check if lockout timer starts.
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Reset — make sure it’s not reclosing again.
With something like ROOTS and Quasar, this is a breeze — set up the sequence, define delays, and automate. No more stopwatch testing.
Nobody ever gets blamed when a relay doesn’t reclose — until one does when it shouldn’t. Test the full logic. Test failure cases. Don’t stop at “it tripped.”
Because real protection isn’t just about reacting. It’s about reacting correctly — every single time.
