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Reliance DC Flexpak 3000 drives causing motor bearing failures

We have been using Reliance Flexpak 3000 DC drives to supply the conveyance drives on our machines for about 7 years now and have experienced frequent motor bearing failures due to voltages being induced into the rotor and discharging through the tail bearing. I realize this is a common problem in the drive industry but we also use many other types of drives AC PWM, AC Sensorless Vector Drives, And Minpak DC drives from many other manufacturers including Allen Bradley, Lancer, Toshiba and we have not seen the bearing failures with these other drive systems. Does anyone have any suggestions to prevent these effects and limit the voltages induced. We have run tests by isolating motors and found 70 VAC on the motor casing to ground. In talking with Reliance support they suggested building a filter on the output of the drive to smooth out the waveform but they couldn't spec out capacitor and inductor values because each filter application would be speed, load dependant. Thanks in advance for any help

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Hiya. Yes, you have a problem. When motors started failing around 1997, VVVF drive manufacturers finally did something about it. In a Technical Paper I have from PDL Electronics, dated 13 August 1999, it states "the coupling mechanisms are usually attributed to dissymmetry effects and homopolar flux effects within the motor design or electrostatically induced rotor charge accumulation coupled from the load.". Cute.

There are a couple of ways to get around this:

  1. Fit a filter, as you say.
  2. Change the motor drive-end bearing to an insulated one.
  3. Replace the drive.

For the drive to be showing these sort of problems it must be getting on 10 years old and you probably can't get parts for it any more.

My advice - just replace the entire drive with a "modern" one and be done with it. Building a filter is a waste of time and money.

Good luck, Cameron:-)

Reply to
Cameron Dorrough

Yaskawa is just introducing a G7 drive that is supposed to get rid of this problem. I sell Yaskawa and I just received a flyer for a seminar about them. I haven't seen one yet, but from the info I received, they are the next hottest thing to hit the market. They have a lot of other features you may find helpful. I don't think the G7 is on the Yaskawa web site yet.... but it should be soon.

Craig

Reply to
C What I Mean

I don't know of any drives currently on the market that DO have this problem. Is Yasakawa one of them, perchance? Personally, I've not heard of them..

Cameron:-)

Reply to
Cameron Dorrough

This phenomena of bearing pitting is indicative of VFDs with PWM output sections... which is just about all of them. Filters, grounding brush kits, or things like conductive grease or isolated bearings will help. It shows up with some motors and not with others. It is hard to predict in all cases. But, when the problem comes up, it is a combination of the PWM and the motor as well as other factors. We use lots of VFDs and have never had that problem with our systems that I know of..... But a few people we do service for have the pitting regardless of what drive they use.

I don't believe it is a 100% predictable behavior given field wiring and conduits and so on... But I may be wrong.. I haven't paid a lot of attention to it because it has not been an issue for us to date.

Yaskawa is the manufacturer of many private labeled drives. They made EMS, Magnetek, IDM, and Saftronics until recently. They are a very large manufacturer of VFDs. Good drives as well. Anyway.. the reason I bring it up at all is because of the seminar about their new drive. It has a different type of output configuration supposedly. It might be worth checking out. I will know more in a few weeks.

Reply to
C What I Mean

I must apologize. I didn't read your post very well. I was talking about pitting problems with respect to VFDs. You were asking about a DC drive.

I was half asleep... sorry about that.

Reply to
C What I Mean

To sum up: DC Drives started life as PWM and then became VVVF in line with their AC counterparts. Initially, drive manufacturers didn't fit output filtering (smoothing) for simple cost reasons and, in truth, on some of the older motor designs you probably didn't need it. Going from PWM to VVVF just made the problem more complex.

But, as time passed and more and more customers reported problems, they fitted finally filters to the output as a matter of course. I repeat my statement that I don't know of any drives currently on the market that have this problem.

Cameron:-)

Reply to
Cameron Dorrough

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