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Redesign of 60 Hz motor

Redesign of 60 Hz motor

Redesign of 60 Hz motor

(OP)
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.

RE: Redesign of 60 Hz motor

Why not get a couple of boost xfrmrs and get the right voltage?  He already has the VFD.

It's what I'd do.  But both would work..

Keith Cress
kcress - http://www.flaminsystems.com

RE: Redesign of 60 Hz motor

(OP)
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.

RE: Redesign of 60 Hz motor

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 - http://www.flaminsystems.com

RE: Redesign of 60 Hz motor

(OP)
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.

RE: Redesign of 60 Hz motor

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

RE: Redesign of 60 Hz motor

(OP)
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 ?

RE: Redesign of 60 Hz motor

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

RE: Redesign of 60 Hz motor

(OP)
Thanks starkopete. Yes, A rough back of envelop calculation gives a 10% reduced turns.

RE: Redesign of 60 Hz motor

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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RE: Redesign of 60 Hz motor

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

RE: Redesign of 60 Hz motor

Yeah you're right, 415V 60Hz / 346V 50Hz; same thing. Derrrr.... never mind. morning

RE: Redesign of 60 Hz motor

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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RE: Redesign of 60 Hz motor

(OP)
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.

RE: Redesign of 60 Hz motor

Here is 256T 10hp 1200rpm 460vac 60hz
http://www.reliance.com/cgi-bin/explode.pl?P25G3206

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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RE: Redesign of 60 Hz motor

(OP)
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.

RE: Redesign of 60 Hz motor

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:
http://www.reliance.com/pdf/pdf/acds/611740-531.pdf

256T first line here:
http://www.reliance.com/pdf/pdf/acds/611740-1.pdf

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.  

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Redesign of 60 Hz motor

(OP)
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.

RE: Redesign of 60 Hz motor

Pete, check the shaft sizes.

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

RE: Redesign of 60 Hz motor

Good point. I only scanned accross the first line of the table and didn't go down to the 2nd table.   Now I know - U frame and T frame do not seem mechanically interchangeable even if they have the same major dimensions (i.e. shaft height and foot width correspondin to 256).

=====================================
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RE: Redesign of 60 Hz motor

At this small size, why not buy two new 10kw IEC motors and adapt them mechanically to the application.  Then use the drive to overspeed them to 60hz.

The problem with rewinding to 415V 60hz is that your available torque over the zero to 1200rpm range would be lower, assuming the same FLA as at 460V.

If you could rewind with larger conductors to raise the FLA to get the torque back to the original level, you would be ok but it is unlikely the slots will accommodate the larger wire.

Some of the motor rewinders on here surely could comment on that.

RE: Redesign of 60 Hz motor

(OP)
DickDV

I am a motor rewinder myself. :0)

Ours is a 415 V world. VFD output voltage is 415 V max. So, how would one get 60 Hz at 415 V ?

Rewinding to 415 V, 60 Hz from 460 V, 60 Hz means a 10% reduction in turns, which will be compensated by increase copper cross section to handle the higher current at 415 V. And the drive too can handle the increased current.

RE: Redesign of 60 Hz motor

Good info, edison123!  I still think buying new metric motors would probably be best but it sounds like the rewind, as long as a higher FLA is acheived, would be a good option too.

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