Redesign of 60 Hz motor

[edison123]

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.

 

[electricpete]

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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[DickDV]

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.

 

[edison123]

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.

 

[DickDV]

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.