AIR circuit breaker
AIR circuit breaker
(OP)
Hi All,
Air circuit breaker How to check contact resistance using current injection method feed back appriciated.
Air circuit breaker How to check contact resistance using current injection method feed back appriciated.






RE: AIR circuit breaker
The "DC" thing is to make sure you're measuring just the resistive component of the circuit impedance. Using AC, the voltage drop contains both resistive and reactive components, and a significant change in resistance could be masked by a large reactive component.
Or use a DLRO (digital low resistance ohmmeter). Several companies manufacture them and they're made for this type of measurement.
Or call your friendly local testing company and have them drag their equipment out and test the circuit for you.
I'm not being flippant here, but there are a few tricks to determining exactly what's going on with a questionable reading.
old field guy
RE: AIR circuit breaker
RE: AIR circuit breaker
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If we learn from our mistakes I'm getting a great education!
RE: AIR circuit breaker
http://www.aemc.com/products/pdf/2129.80.pdf
Readings depend on frame size but should never be higher than 50% of the lowest phase.
Or go here to find a tetsing company in your area
www.netaworld.org
RE: AIR circuit breaker
There was a pretty extensive article a few issues back in NETA World, the technical magazine of the interNational Electrical Testing Association concerning the use of AC in testing contact resistance.
It's an interesting read. The basic thrust of the article is the errors to which I referred.
That said, the AC millivolt drop test is better than no test at all.
DC high current sources are actually fairly common around industrial facilities, cleverly disguised as arc welding machines.
old field guy
RE: AIR circuit breaker
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If we learn from our mistakes I'm getting a great education!
RE: AIR circuit breaker
http://www.netaworld.org/files/ItemFileA1335.pdf
RE: AIR circuit breaker
As a documented test the article has some large gaps and certainly doesn't "say it all", but it raises some questions which are worth pursuing. I have access to a high current DC source (>500A), a PCITS and an accurate voltmeter but am somewhat pressed for time at present because of generator outages. I will try to carry out a more clearly documented test, including equipment types etc and connection details and note of any additional components such as CTs one the bar, and will post the results. Perhaps your colleague could do the same and we can compare results?
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If we learn from our mistakes I'm getting a great education!
RE: AIR circuit breaker