Effects of 50Hz on a 60Hz motors. 2

[mikepz]

I have a numerous 3-phases motors ranging from 220V 60Hz to 480V 60Hz. I understand that these motors would overheat if I run them at 50Hz. What can I do to run these motors at 50Hz ?

Thanks you much for your responses.

 

[edison123]

Marke & aolalde,

I do not for a moment dispute the theory to maintain V/Hz in electrical machines (trafos included).

I recommend to my clients to always try the 60 Hz motors at 50 Hz and watch for the abnormal temperature rises, before deciding on rewinds, which is a costly proposition. The fact that the clients imported these motors second-hand (as part of whole system) speaks for their economic priority.

Except for some 2 pole motors, the recommended motors are working with temperatures well within limits of B class. I based my recommendation on the fact that these were very old (30 odd years) sturdy motors with good factor of safety (unlike the modern motors which are always on death wish) and that a reasonable risk can be taken with them without any major problems.

Believe me, as a rewinder, I would have been happy to rewind them and make some money. My curiosity (whether they will really fail) got the better of me but it has earned the goodwill of my clients.

 

[DougDavis]

Forget the BS about Flux!

Those countries with 50Hz power systems provide that power at "standard" or "nominal" voltages just like the U.S. The most common voltage in 60HZ 3-phase countries is 480VAC (nominal).
The most common voltage in 50Hz 3-phase countries is 400VAC (nominal). Get a good quality VFD that will run on the Canadian systems, which are 60Hz 600VAC nominal. Just like Mikey, they will eat anything.

Configure the VFD to run your 60Hz motors at 60 Hz. I have thousands of times shipped machines in this configuration, from the Philippines to India. Even attaching the input of these drives to 600VDC systems then running 3-phase motors at 60 Hz, or any frequency needed.

 

[Marke]

Hello mikepz

This thread seems to have moved in a number of different directions. Perhaps it is time to go back to your original question "I have a numerous 3-phases motors ranging from 220V 60Hz to 480V 60Hz. I understand that these motors would overheat if I run them at 50Hz. What can I do to run these motors at 50Hz ?"

1. Yes, if you operate these motors at the same voltage, but at 50Hz, there is no coubt that the iron loss will be increased significantly and in many cases this will lead to damage to the motor. While some have experienced no short temr failure from this practice, others have so I would suggest that you take care if you choose this option.
2. The motor will spin at 5/6 speed and this may affect the operation of your machine.
3. You can safely run the motor at 50Hz (lower speed) provided that you reduce the voltage to 5/6 of the 60Hz voltage, and you reduce the load to 5/6 of the 60Hz load.
4. You could rewind the motor for 50Hz 220 volt operation, but you may still need to derate the power output of the motor. 50Hz needs more iron for the same power rating.
5. You could use a variable speed drive to convert the 50Hz to 60Hz and run your motor as normal. (Must be three phase motors)

Mark Empson

http://www.lmphotonics.com

 

[jbartos]

Suggestion to edison123 (Electrical) May 1, 2004 marked ///\\
I recommend to my clients to always try the 60 Hz motors at 50 Hz and watch for the abnormal temperature rises, before deciding on rewinds, which is a costly proposition.
///The "watch" for the abnormal temperature rises may prove to be detrimental to the motor; especially, when it is totally enclosed. Which method do you recommend to "watch" for temperature rises?\\

 

[edison123]

jb,

The same way as you would "monitor" as per your april 8 post in thread237-91817.

 

[jbartos]

Comment: One way to monitor the temperature is to use the motor terminal box access to the motor interior space, if there is any opening available inside the terminal box. Usually, there is one along the leads coming from the motor windings. If this is not possible, the access to the motor internal windings is more difficult. Potentially, a small opening can be created for temperature sensor and after the measurements are done, the opening may be tapped and machine screw used to close the opening.

 

[SteveKW]

Some motors do just fine 50 or 60 hz...

http://www.leeson.com/cgi-bin/fetchpdf.cgi?/literature/bulletins/pdf/1050/AC50Hertz.pdf

See page 68.

 

[jbartos]

Suggestion to the original posting marked ///\\I have a numerous 3-phases motors ranging from 220V 60Hz to 480V 60Hz. I understand that these motors would overheat if I run them at 50Hz. What can I do to run these motors at 50Hz ?
///Beside a lot of good advice in the above postings, the motor manufacturer tech supports might be contacted for recommendations. The manufacturers should know whether the motor has any design constraints preventing one running the motor at 50Hz. What if the linear scaling from 60Hz to 50Hz is not linear; therefore, it may or may not be "very accurate."\\\