OT - Rewinding Motors

Sorry this is OT. I have a vendor (in Germany) who is telling us that the motors they have ordered (as per the original contract) are rated at 60HZ, 440VAC +5%/-10%. The facility power is nominally 60HZ, 480VAC.

The vendor is asking for a substantial amount to replace motors for new ones rated for 480VAC or, they suggest, we could possibly rewind the originals to run at 480.

I have had no luck getting true motor specifications for the original motors, so I am working blind at the moment.

My questions are these:
1) What is the "reality" of running 440VAC +5%/-10% motors at 480VAC - Will they be damaged? If not, will there likely be any issue at all?
2) If I can't use them as is, is it reasonable to think that they can be rewound to run at 480V?

This equipment is very-long lead and I only have the three options - Use the originals as-is, rewind, agree to pay for new.

Anybody know about this?

Thanks,

Steve

Hiya Steve,

How many motors per machine? What is the total horsepower?
You might be able just to put in an isolation transformer to feed the entire thing, and tap it down to 440VAC out.

A 480V/440V auto-transformer will be cheaper than a 'real' transformer.

edit: Found one that custom makes them in the US:
http://www.marcustransformer.com/uploads/marcus_product.pdf1/Type%20MAT0001.pdf
They dont have 480/440 in the selection chart. But they could make one special for you.

My understanding is that it is not economical to rewind small drives - cheaper to buy new motors - unless they are "Special" i.e. non standard.

Perhaps the supplier is being a bit akward and views this change as a way of getting some more profit from the project. Maybe I'm too jaded!!

Think the transformer would be the way to go.

I have used Sola Hevi-Duty buck-boost transformers in this situation before. Depending on the full load current required by the motors, this may work for you. Basically the motor current runs thru the secondary winding which is sized to drop the 9% or so required to achieve 440V. But, if you are using a VFD just set the limits to 440V and be done with it. Good luck!

Thanks for the quick replies.

This is a very large machine with a combined total of about 290HP (or 216KW) in motors.

Given the size of the drives- now I would try to get the full motor specs from the manufacturer as they may well work on a wide range of voltages.

Steve
I think I would talk with the motor builder.

The 40 volt difference is around 9%. I would be tempted to try running them on 480. I am kinda suprised at +5 and - 10% specs on voltage. I thought over voltage would be better tolerated than undervoltage ASSUMING full loaded motors.

How are they started - across line?
How often started?
What is load pattern -- steady full load or like that of a press medium then high load every 30 second?
What is largest motor size?

A soft start would reduce problems when starting ie lights dimming and power bill demand factor. Also would reduce wear and tear on couplings and driven components from fast speed change on startup.

VFD would also give you soft start and as mentioned you can set upper voltage to 440. If motors are inverter rated you are completely in business.

Dan Bentler

And there be the rub.

This manufacturer is, shall we say, less than giving. Theis machine has been on order for better than a 1-1/2 years (not unusual for this equipment, believe it or not) and not many alternatives are available.

I have been requesting the motor specs now for well over a month (through the Project Manager) with little or no response. The only thing we are getting is that the machine builder is SAYING "440 +5/-10. No more". But then they want the money. So who knows.

Anyway, regardless of that reality, I need to be prepared with possible alternatives such as cost to rewind, probability of damage if run @ 480, transformers, etc.

Steve

Dan - Once again, I am up against a manufacturer who is holding most all the cards and not showing. I don't even have schematics at this time. We all "feel" that 480 will "probably" be OK, but they are German motors and I don't know what the reality is.

I checked a couple of suppliers, Brook Hansen and SEW eurodrive. 460v seems to be the "Standard" for USA and Canada.
SEW even say the "Supply" is 480 but the motor is rated at 460!

440v seems a "Special" voltage!!!

I agree completely. 480 is standard in the US and Canada, no doubt, but I don't know about Germany. What I do know is that the vendor's quote does state 440. Why nobody caught this back then, I have no idea - I didn't work here then, but that's really not a point. No use crying over split milk and all that.

Now I need to learn about German-built 440V motors, their real capabilities, and rewinding.

Steve

The company I work for manufactures motors, I know that for upto & including 440V motors we use grade "1BS" copper winding wire, for 480V and above we move to grade "2BS" and further phase insulation paper between the stator poles.
You could find that 480V is fine for your motor just that the insulation breaks down sooner than expected.

EDIT - this is self bonding copper wire

The odds are strongly in favor of the motors being just fine on 480V. This is even more true if the motors are not continuously loaded right at their maximum rating.

Asking a motor rewinder to rewind a 440v motor to 480v would, in most cases, get you an incredulous stare and, hopefully, a polite question "why?"

Older 440v motors are running all over the US on 480v power successfully everyday.

Now, if somehow, these motors are very tightly designed and 440 + 5% is absolutely all they are good for, I would think that a small buck transformer in the motor leads would be cheaper than any other option.