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Old 05-23-2014, 03:20 PM   #1
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Default I'm a roller, A high roller baby.

This is the third time I have rolled phases to balance a motor
Brand new Baldor 480v 60 hp, driving a centrifugal pump. FLA 72 SF 1.15. Tripping the conservative 75a O/L's. I bumped em to 80.
When I got there 78, 78, 66
First roll 72, 72, 81
Second and final roll 74.5, 75, 75.5
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Old 05-23-2014, 05:18 PM   #2
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Quote:
Originally Posted by farlsincharge View Post
This is the third time I have rolled phases to balance a motor
Brand new Baldor 480v 60 hp, driving a centrifugal pump. FLA 72 SF 1.15. Tripping the conservative 75a O/L's. I bumped em to 80.
When I got there 78, 78, 66
First roll 72, 72, 81
Second and final roll 74.5, 75, 75.5
I can honestly say I have no idea what you are talking about.

What is "rolling phases"? I have never heard this term.

Also, if your motor FLA is 72, and you are drawing 75+, you have a problem. You didn't fix it by "rolling phases" (whatever that means). Time to do a little more digging. Maybe the motor is too small for the application, or there is some other kind of mechanical issue with the system, but you shouldn't be drawing FLA under normal circumstances.
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Old 05-23-2014, 05:33 PM   #3
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Rolling is moving A to B, B to C, C to A, etc
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Old 05-23-2014, 06:42 PM   #4
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This may be a stupid question, but doesn't that reverse the direction of the motor?
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Old 05-23-2014, 06:50 PM   #5
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A-B or B-C would. I'm hoping to learn something in this thread very soon
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Old 05-23-2014, 06:55 PM   #6
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The motor rotation is not changed.
ABC=BCA=CAB as far as rotation goes.
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Old 05-23-2014, 07:05 PM   #7
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The motor rotation is not changed.
ABC=BCA=CAB as far as rotation goes.
Cool, thanks! I didn't know that. Learned something new today! It's a good day with a 3 day weekend ta boot!
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Old 05-23-2014, 07:19 PM   #8
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Interesting. Jraef mentioned using the same solution when getting intermittent overcurrents on Y/Δ starters. If your voltages are the same, I'd be hard pressed to explain what was going on to balance current like that, but I'll keep that trick in my hat.
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Old 05-23-2014, 07:34 PM   #9
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here's a paper on dealing with motor current imbalance, referencing rolling phases...

~CS~
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Old 05-23-2014, 07:37 PM   #10
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Current looks good,What is the voltage reading. i think the o/l s too low.
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Old 05-23-2014, 07:38 PM   #11
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Interesting. Jraef mentioned using the same solution when getting intermittent overcurrents on Y/Δ starters. If your voltages are the same, I'd be hard pressed to explain what was going on to balance current like that, but I'll keep that trick in my hat.
It's because there are always imperfections in the motor, and there are always differences in phase voltages. So "rolling" helps to line up the two sets of conditions to hopefully compliment each other to achieve better current balance (i.e. motor nirvana...). You have 3 chances, hooking it up once and getting it right is, statistically, unlikely.

Doesn't always work, but it's free (other than time).
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Old 05-23-2014, 07:52 PM   #12
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The imperfections in the motor are likely constant, but are the differences in the phase voltages? I would think not.

So the "fix" would be temporary, no?
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Old 05-23-2014, 08:25 PM   #13
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Submersible pump motors and hermetically sealed refrigeration compressors are notorious for needing to be rolled. It almost always helps, at least to some degree.

I've come back to some of these months or years later, rolled them again, and the original roll was still best.

In my experience, motors supplied by wye connected systems will benefit more from rolling that ∆ systems. It doesn't seem to matter much what internal connection the motor is.
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Old 05-23-2014, 08:40 PM   #14
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It's because there are always imperfections in the motor, and there are always differences in phase voltages...
We don't test impedance, but there are tests we do that are directly dependent on impedance, and the expected deviation between phases we see is usually less than 1% for large (100HP+) motors. Most system voltages seem to be balanced within about the same range of 1%.

I don't doubt that it works, but I just can't figure how that solves current imbalances of 18%, which seems wicked high.

Farls, is there a chance you can get actual voltage measurements to go with those currents?
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Old 05-23-2014, 08:48 PM   #15
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Could it also be freq/waveform slight imperfections? I'm really struggling with this concept.
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Old 05-23-2014, 08:49 PM   #16
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Not doubting. Just trying to wrap my mind around it.
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Old 05-23-2014, 10:44 PM   #17
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Voltage was perfectly stable at about 476 - 478. The impeller is improperly desiged and needs to be modified or changed. The people who built it have been made aware and agree.

In the mean time I have shut the pump in as much as I dare to get the current that low and I am comfortable with it.

When I first got there it was actually 94 94 78.

A little unrelated to this story but, I have found rolling can make a HUGE difference when using a rotophase.
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Old 05-24-2014, 06:50 AM   #18
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Quote:
Originally Posted by farlsincharge View Post
This is the third time I have rolled phases to balance a motor
Brand new Baldor 480v 60 hp, driving a centrifugal pump. FLA 72 SF 1.15. Tripping the conservative 75a O/L's. I bumped em to 80.
When I got there 78, 78, 66
First roll 72, 72, 81
Second and final roll 74.5, 75, 75.5


I never heard of rolling phases before.
I just assumed by moving phases you would reverse motor.
But it makes sense now by moving all 3.
Thanks for the info,
Have to put that in the vault could come in handy latter.


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Old 05-24-2014, 07:31 AM   #19
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Rolling rolling rolling keep that phase rotation going.


OMG I've become Chicken Steve.
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Old 05-24-2014, 08:17 AM   #20
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Quote:
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Rolling rolling rolling keep that phase rotation going.


OMG I've become Chicken Steve.
No you didn't, I didn't have to look up anything you wrote in the dictionary, or google it.
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