RCM-2009 Reliability Centered Maintenance Managers' Forum - March 23-26 - Daytona Hilton Ocean Walk Village - Daytona Beach Florida Join or Manage Your Profile Posting Boards Machinery Condition Monitoring and Predictive Maintenance Posts About vibration/alignment/balance Twin motor problem
Join or Manage Your Profile Posting Boards Machinery Condition Monitoring and Predictive Maintenance Posts About vibration/alignment/balance Twin motor problemPage 1 2
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Ron,
Thanks for the info. I can't think of a reason for 2 inverters either except the possibility that the OEM's inverter supplier (probably the one with the lowest cost) doesn't make large enough drives and they wanted to be price competitive. Danny |
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Ron, Can you tell me where I can find some documentation on this? I am dealing with a similar problem now. My motor has 1 insulated bearing that appears to work good for a while but eventually gets taken out by shaft currents. Any information you can provide on this subject would be appreciated. Travis Hudson |
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Thud,
See my response on the first page concerning inverter duty cable. Ron Is this an AC or DC motor? |
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Ron,
It's a 2000 hp, 1800 rpm, AC motor made Teco Westinghouse. We measured shaft voltage at 3.2 volts while test running it in the shop. I was hoping you could tell me where to find more information on the subject before I approach our in-house electrical guys. Travis Hudson |
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Thud,
Was it operating on a VFD? If not, it sounds like you have a prime candidate for insulating the NDE to prevent internal circulating currents. If you are on a VFD, how do you cable the motor to your test stand? Ron |
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Ron,
No, the motor does not operate on a VFD drive. It has a "soft start" installed and it does have an ceramic coated, insulated bearing on the NDE. I was hoping you had some more information on the European wiring practices and codes that you spoke of in your earlier post. Travis |
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Another piece of the puzzle of the ongoing saga.... The couplings were pulled on the motors and the coupling on the east motor was worn pretty good. It was full of iron fillings and rust. Now when I look at the machine machine speed though on the PI system there always seems to be a mismatch of motor speeds. At times 4 rpm difference. Even when one motor is holding steady for 10 minutes the other motor will flucuate speed.
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Aubrey,
Everything points to an improper setup of the drives. The results point to torque pulsations. Have the drives folks back in or better yet horse whip the design engineer! |
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Thud,
The paper that really opened my eyes was authored by Mr. Patrick Link of ABB. I believe it was published by IEEE in 1995. Sorry, it is copyrighted, so you will need to approach them for a copy. It has resolved ALMOST every EDM issue I have faced. Ron Brook |
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An update on the motor situation here. They did not change out the east motor, just the coupling. Since then they have run it up a few times over 500 rpm with no problems. At least not yet. It could be the coupling is holding the motors together. We will see.
I asked another person about the quad varible drives. He said in the late 80's when this arraingment was made it was all they had. This fellow has worked on drives out here a looong time and I really would take his word. Thanks for all the help guys, Aubrey |
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Aubrey,
As I recall, in the late 80's 200 hp was about the maximum for an inverter. You may have mentioned it and I couldn't find it, but what kind of coupling is in use? Has alignment been verified? Have the coupling seals and lubrication been properly maintained? Danny |
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Hey Danny,
They realigned the motors to the pump when they changed out the coupling. No one can tell me how bad it was out of alignment. The geared coupling they pulled out was shot. Lubrication was probably an issue. The o-rings on the coupling were questionable. Aubrey |
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If nobody can tell you what the alignment was before, it was probably pretty bad. That will almost always lead to o-ring failure and lube loss in a Falk or other gear coupling that uses o rings for seals.
A few years ago, Falk guaranteed that if their alignment tolerances (very loose) were met and you used their Long Term Grease (coupling grease) the coupling would last at least 5 years without relubrication. Was the bearing that failed adjacent to the worn coupling? Danny |
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Actually, no. It was the opposite bearing that failed. I had not even thought much about that.
Aubrey |
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