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Motor Has No Power


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#1 Darren

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Posted 24 January 2009 - 03:07 AM

I have a lathe with a Fuji VFD that appears to be suffering from a loss of power. If I remove all the mechanicalaspects of this problem I am left with the fact that I can significantly slow down a 37KW Spindle motor with a short(30") 2x4. Firstly the owner of the machine sent the drive out for test/repair to the Fuji distributor in California. They said the drive is fine and it ran on load without problem. Then they installed a new PLG on the motor. Then they called me, I should have stayed home. I checked the motor with the megger, no problems. Then I checked the current to the motor when the motor was under load. I had the motor running at 3000rpm, 4800 is max, and measured 80 - 90amps each leg. So I removed all the belts so it was just the motor. Itstarted fine and got up to speed as expected. Then with the 2x4 on nthe pulley I was reading 90 amps on all legs and was able to slow the motor by 1000rpm. I removed the motor and off to the motor shop I strode. The motor guy duly opened the motor and tested. ohmemeter says windings OK growler says rotor ok.

Where do I go now?? What can be wrong with the motor to allow this to happen?
How does torque limitation work? does it limit the current ?

thanks in advance
Darren

#2 jraef

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Posted 26 January 2009 - 03:50 AM

QUOTE (Darren @ Jan 23 2009, 07:07 PM) <{POST_SNAPBACK}>
I have a lathe with a Fuji VFD that appears to be suffering from a loss of power. If I remove all the mechanicalaspects of this problem I am left with the fact that I can significantly slow down a 37KW Spindle motor with a short(30") 2x4. Firstly the owner of the machine sent the drive out for test/repair to the Fuji distributor in California. They said the drive is fine and it ran on load without problem. Then they installed a new PLG on the motor. Then they called me, I should have stayed home. I checked the motor with the megger, no problems. Then I checked the current to the motor when the motor was under load. I had the motor running at 3000rpm, 4800 is max, and measured 80 - 90amps each leg. So I removed all the belts so it was just the motor. Itstarted fine and got up to speed as expected. Then with the 2x4 on nthe pulley I was reading 90 amps on all legs and was able to slow the motor by 1000rpm. I removed the motor and off to the motor shop I strode. The motor guy duly opened the motor and tested. ohmemeter says windings OK growler says rotor ok.

Where do I go now?? What can be wrong with the motor to allow this to happen?
How does torque limitation work? does it limit the current ?

thanks in advance
Darren

Most likely you have inadvertently connected the motor incorrectly. You have not described what voltage your power source and drive is or what the motor nameplate says, but I would expect that you have connected it in Star when it should have been connected in Delta or vice versa.
"He's not dead, he's just pinin' for the fjords!"

#3 Darren

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Posted 26 January 2009 - 01:18 PM

The motor has only 3 leads. It is a 220V motor 37KW. There was no changes to the drive or the motor before the problem started. One day everything is hunky dory the next .....!

Thanks
Darren

#4 marke

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Posted 26 January 2009 - 06:05 PM

Hello Darren

When you load the motor and it slows down, either the VFD is reducing it's output frequency, or the motor is slipping.
What does the frequency/speed display on the drive indicate when the motor slows down?

If the frequency stays constant and the motor slows down, then it sounds like there is either a rotor problem, or the motor is underfluxed. I would suggest that you try running the motor directly off the incoming supply without the VFD and see it it then produces full power at full speed. If it does not, and slows down under load without the VFD, then there is a problem with the motor.

If the VFD slows down with the motor, it is probably a setting on the VFD that is not correct and it sounds like current or torque limiting is set incorrectly.

Best regards,
Mark.




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