Motor reversing

[neal5105]

Good day all,

I have a 2.2KW motor installed in a milling plant.The motor is 400v 3 phase 4 pole.
The motor starts and stops by means of a level switch that contols a contactor. The switching is frequent ie evey 2 seconds.

Now heres the problem. The motor will run fine for a few day and the the direction will sudenly change. When this happens there is no problems and it will run in reverse as long as we leave it. I then have to change phases to get it to run in the correct direction. All if fine for a few day and then the direction will change again.

There are about 10 other motors on the main board but only the one motor has the problem.

Now please feel free to tell me this cant happen because that is what i told the customer the first time he told me.

 

[electricpete]

Personally, I don't see how difference in timing of contact closing can possibly have anything to do with this.

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[rbulsara]

Pete:
Probably not, that is why my fingers are crossed. But stranger things have happened to me while "solving" apparent mysterious issues.


Rafiq Bulsara

http://www.srengineersct.com

 

[electricpete]

Intermittent failure-to-close of one phase could be the problem (not millisecond timing differences). So replacing the contactor may address the problem from that standpoint. Let us know.

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[OperaHouse]

A random bad contact on a MC could cause it to reverse, BUT think what happens when a generated phase reconnects with the out of phase power. Find it hard to believe this problem is so polite as to only do it at startup.

 

[waross]

What are the other loads on the MCC?

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

 

[mns15451]

Measure the current on each phase while operating in either direction. It will give the clear picture of the happenings.