440V Motor On A 480V Supply?

[ThePunisher]

One of our clients specified 480Vac, 60Hz, nominal system voltage to feed their 440Vac, 60Hz motors.

Is there any concerns on this since the motors may be subjected to an almost 110% of nameplate voltage (assuming system is lightly loaded).

 

[dpc]

This was the standard motor rating for 480 V systems back in olden times. The difference in voltage was to account for the voltage drop between the source and the motor. With larger 480 V systems, the voltage drop became generally lower and the nominal motor voltage was increased to 460 V.

A standard NEMA motor should be good for continuous operation at 110% of nameplate. Even if the voltage at the MCC is 480V, the voltage at the motor will be less.

If these are old 440 V motors, they will probably be OK. They seem nearly indestructible sometimes.

David Castor

http://www.cvoes.com

 

[ThePunisher]

Thanks David!

 

[waross]

How old are these motors? In Canada supply voltages were standardized as multiples of 120V (120V, 240V, 480V and 600V) in the fifties. I may be wrong but I was under the impression that motor voltages were standardized as multiples of 115V (115V, 230V, 460V and 575V) at about the same time.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Bill,
The old standard (or I should say an old standard) for equipment voltages here in the US was 110 / 220 / 440, but was changed some time ago in an effort to standardize. Now the official equipment voltages are 115 / 200 / 230 / 460 and the distribution voltages are 120 / 208 / 240 / 480.

I laugh when I see new cheap motors come in from China with nameplates that say 220/440V, because it probably means they found some old design documents and built to them, without even bothering to find out that we don't use those values any longer.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[magoo2]

Keep in mind that the nominal 480 V is probably +/-5% if they follow ANSI C84.1. This gives you a high end of 504 V which is almost 15% higher than the motor nameplate and would present a problem.

 

[jraef]

It is for the newer motors with 440V labels as I described above for sure, but in my experience the older 440V labeled motors had much wider voltage tolerances, whether by purposeful design or by "fudge factor" engineering that was more common back then. I haven't seen any problems with them running on 480V nominal systems.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

I second jraef's comments. I asked the age of the motors.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

By the way, by "old" I meant pre-1965, the old "U Frame" motors, which is primarily where I have seen the 220/440 nameplate voltage.

But certainly, anything 1965 and up is not "old" from my perspective...


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[ThePunisher]

This might be a shocker guys but then motors are NEW and was specified by our client in their respective datsheets. The application is for a mining company in Brazil.

I am still at limbo as to where this rating came from as far 480V nominal voltage application is concerned. I might raise this as a TQ later. I am wondering if these motors will work fine on 480Vac system consdering that their are near their maximum voltage threshold.

 

[LionelHutz]

Hook one up, loaded or unloaded. If the no-load current is high, say >60% of the FLA, or the loaded current is > FLA then they likely won't work.

Sounds like the customer has specified them and now already has them so they are likely stuck with them either used or still new.

 

[dpc]

You probably have some control of the 480 V system voltage via transformer taps.

David Castor

http://www.cvoes.com

 

[ThePunisher]

My warm thanks to all your contributions. I looked deeper into their motor datasheets and there is an item there that requires the capability of the motor to be operated continuously at 10% overvoltage.

This will figure why they allow 440V Motors on 480V system nominal. The next thing to do then is to keep an EYE on the vendor specifications to ensure this requirement is met.