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Redesign of 60 Hz motor

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edison123

Electrical
Oct 23, 2002
4,506
The client has imported a Baldor 60 Hz, 7.5 HP, 460 V, 1170 RPM into a 415 V, 50 Hz environment along with the connected equipment. The connected equipment (a clutch) is asking for the original 1170 RPM. He is using a VFD to run this motor. Given the drive input voltage is only 415 V, he is not able to run the motor at 1170 RPM and the motor has already failed within a few hours of running. The drive was tripping on current limit.

I am thinking of redesigning the stator for 415 V, 60 Hz so that he can get his 1170 RPM.

Any opinions ?

The Baldor motor original spec sheet is attached.
 
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Keith

I thought about the boost trafos too. But now that the motors (2nd one too failed today) have failed, it would be cheaper to rewind for 415 V, 60 Hz.
 
I guess I'd agree with the exception that I thought the cost to re-wind was more than the cost of new motors up to maybe 15+hp. But I'm not sure. But then a new motor and tafos would probably still be more than a rewind so... Yeah, I guess I agree with you.

Keith Cress
kcress -
 
I advised the client to ask OEM's to supply 415 V, 60 Hz but no dice.

Yes, it will be cheaper to rewind where I am.
 
On 600 V is it connected in wye or delta? A change from wye to delta would solve the problem.

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

It's 460 V, 60 Hz. Anyway, now it is all a moot point since the motoes have failed.

Do you any problem in rewinding it for 415 V, 60 Hz ?
 
Hi,
I can't think of any problems with the voltage change.
T2 = T1 X E2/E1, where: T2 is new turns per coil, T1 is original turns per coil, E2 is new rated voltage and E1 is original rated voltage.

Thanks
 
Thanks starkopete. Yes, A rough back of envelop calculation gives a 10% reduced turns.
 
Might I point out a littel tiny problem with this?

How are you planning to get to 1170 RPM even with the 415V input voltage? You STILL have 50 Hz. If you wind it for 6 poles, it's still going to spin at 975RPM (assuming 2.5% slip from the 1170 RPM value). So to goose that to 1170 you are still going to need to run at 60Hz.

Unless; are you planning to wind it as a 346V motor and then over speed it to 60Hz with a 415V supply?


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Hi,
If I understand the original post correctly the frequency will be the same, only the voltage needs to change. Currently a 460 volt, 60 Hz motor, he wants to go to a 415 volt, 60 Hz motor. The speed should stay the same. (It is a strange voltage/frequency combination).

Thanks
 
Yeah you're right, 415V 60Hz / 346V 50Hz; same thing. Derrrr.... never mind. [morning]
 
Frame 256U - doesn't that mean U frame old style? Maybe that is why a replacement isn't readily available. But there might be adapters available to mount a new T frame motor in place of an old U frame.

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epete

Yes, it is a very old and very used motor. Changing to a T frame motor would not solve the issue.

The clutch needs 1170 RPM. The drive can output 60 Hz but not the 460 V to go with it since the supply voltage is only 415 V.
 
Here is 256T 10hp 1200rpm 460vac 60hz

If it could be mounted with 256U adapter (I have heard of some type of U to T frame adapters... not sure how they work), then I think it should be able to provide 7.5hp at voltages down in the range 400vac that you are talking about.

But it sounds like you have a solution that works.

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jeff - a question for you.

After the motor is rewound for 415 V, 60 Hz, how should I input the drive parameters ?

a. 415 V/60 Hz/1170 RPM or

b. 345 V/50 hz/ 975 RPM

Will the setting (b) affect the torque limit (because running above base speed will reduce torque, at least as the drive sees it) ?

The output speed will be set at 1170 RPM.
 
If you will forgive me - carrying on my own little discussion. The adapters are only relevant for putting smaller size motor in place of bigger motor - not relevant here.

It looks to me that 256U is indeed mechanically interchangeable with 256T.

256U first line here:

256T first line here:

The only difference I could see was term box dimensions which I doubt would make a difference for interchangeability.

So I think you could buy an off the shelf 256T 10hp 1200rpm 460vac 60hz that would do the job and be mechanically interchangeable. (If I am looking at it wrong, anyone please correct me).

Sorry again for the tangent.

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pete

Thanks for all the info. I have saved them for future.

The issue here is 460 V is not available to get the 1170 RPM needed by the clutch. The VFD can output only 415 V and to maintain the V/F (and hence the torque), we need 460 V. So any 460 V motor, regardless of HP, isn't going to work. Hence my decision to rewind to 415 V, 60 Hz.
 
Pete, check the shaft sizes.

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