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Squirrel Cage Motor


bob

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Hi,

 

I wish to share this with you something whic defeats the very basic understanding of electrical engineering, I just got a call from a customer claiming that he could not reverse the rotation of a three phase electric motor. He did change the phase on the terminals of the motor itself but the motor keep rotating in a clockwise direction. There is nothing connected at the output shaft of the motor, its a 1.5 k W 400 V motor.

I will drive there( 8 hours drive ) and keep the forum informed.

 

Bob

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Hi Bob

 

I recently had a similar experience with an installation using a VFD.

The client insisted on reversing the phases at the input to the VFD rather than the output. Once the output phases were reversed, the problem went away.

 

I have also seen people reversing/swapping three phases rather than just two.

 

Interested to see what you find.

 

Best regards,

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It could also be that he has an IMD unit (Integrated Motor-Drive) which has the VFD built right on to the motor.

 

http://danfossdrives.com/images/fcm.jpg

 

So he may not be aware of the VFD. If he is swapping leads at a remote motor starter or circuit breaker, it will have no effect on the motor rotation as Marke pointed out.

 

 

"He's not dead, he's just pinin' for the fjords!"
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Perhaps he has lost a phase? A three phase motor running on two phases with no load connected will often rotate randomly.

One thing that I am sure about, you will not get the full story over the phone unfortunatly.

Good luck and I hope its a pleasant drive.

Kens

An expert is one who knows more and more about less and less until he knows absolutely everything about nothing
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Very true kens. A 6 SCR soft starter in which 1 SCR has an open gate can also exhibit similar behaviour. There again Bob, if the weather is good and the customer is paying, the drive might present as a well earnt break!

 

Regards,

GGOSS

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