Bearing Damage on VFD motor 9

[everest]

We have had the bearings on three centifugal pump motors on three different jobs fail. The pumps have been in service ranging 1 year to three months. We had the bearigs on one motor analyzed, they said the races were fluted (I think thats the right word) due to electric discharge. I know this can be a problem with VFDs but was told it was rarely a problem.

Is there any thing in a particular motor design that can increase the potential for this to occur

 

[Skogsgurra]

You are probably right regarding the du/dt filters. I was thinking of those monsters with diodes, capacitors and feed back to the DC link. They cost a lot.

I also agree that most small motors are just thrown away. But since there are so many, users have to start thinking about why they are thrown away. I had hoped that Gambica had started thinking about that by now.

I see quite a lot of them "throwaways" now. And I try to tell people that there are (relatively) simple ways of extending their lives beyond one or two years. Some do listen, some do not.

 

[mc5w]

This kind of bearing damage also occurs in the wheel bearings of streetcars (trams) and electric locomotives because the traction current returns through the rails. If the bearing was not designed for this service using metal or carbon brushes to bypass current or if the brushes went bad the current would destroy the bearing.

What you have is a high-tech version of a century old problem.

Skogsgurra, thanks for the tip that static electricity from a belt or fan blade could be the culprit. One of my stepbrothers was in a hekicopter transport unit in Vietnam and he would tell me about the he!!atiuos amount of static charge that builds up on a helicopter or airplane when it is flying. When hooking up a sling load to a helicopter the people with experience would throw the nylon ring onto the hook on the bottom of the helicopter and then throw the sling load hook onto the ring and jump off the sling load just before the load hook contacted the helicopter hook. Every newbie would reach up and grab the hook on the bottom of the helicopter with their hand, then his eyes would pop out, and then HE woudl go flying about 20 to 100 feet.

The Human Voltmeter Method never feels good.

Mike Cole, mc5w@earthlink.net

 

[Skogsgurra]

"HarrierHQ"

I received you mail and I have answered it. But it bounced. Postmaster saying that you do not receive mail from my computer. How do we proceed?

Gunnar Englund
GKE Elektronik AB

 

[Hewlett]

Very interesting reading!
skogsgurra: re. your "bearing predictor" circuit. This sounds very interesting. Do you know....is this/ will this "go/no-go functionality" be available in any commercial diagnostic product..?