Random solid state overload failures

[topgrind]

Recently have had random solid state overload failures on various sized 480 volt motor applications ranging from 10Hp up to 200Hp. Most have been while running at a constant load within proper limits.

Not common to swtichboard or transformer feeds to the MCC's

All have been Furnas Solid State Overload Relay with Phase Loss Circuit. I would like to get some input on what may cause the failures and also if there is any predictive technologies or trip tests that would show a possible impending failure.

 

[jraef]

You did not really provide enough nformation.

What kind of failures do you mean? Not tripping when there was an overload? Nuisance trips? In which case, what kinds? Tripping on OL when there wasn't one? Phase Loss?

How did you determine that the "failure" condition did or did not happen, as the case may be from the above questions.

Which Furnas SSOL relay are you refering to? There are several styles. I can guess it is the ESP100, but that would be an assumtion.

Please try to be more thorough.

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[electricpete]

I assume you are talking about a spurious trip (we have had a few with our solid state ITE circuit shield relays).

If you have an SCR on the output of your relay, a good test is to measure the leakage current with a fixed dc voltage with the device off. Or a little bit easier just measure the resistnace but use the same instrument and scale.

You can compare it to sister units or trend over time or sometimes get acceptance values from the manufacturer.

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