Over current on motor with no load?

[Wrongboy]

I have a 40hp 3ph motor that is drawing currents at low to no load that are higher than the FLA rating for the motor. The motor is attached to a centrifugal fan. From my understanding this is backwards. Can anyone shed some light on the for me? Is the motor wired wrong perhaps?

 

[BobM3]

Does the shaft seem to be spinning at or near the rated speed?

 

[controlsdude]

any motor at fla at no load would be a motor that is single phasing or its overloaded. This usually says that the wiring is loose. check all your 3 phase leads from your motor starter, vfd, overload and field terms, and at peker head on the motor.

wired bad and probably wired wrong(loose wires)

 

[DanDel]

Does the current then increase when load is applied?

 

[Marke]

Hello Wrongboy

I do not believe that your problems is related to the direction of the rotation, this will not usually affect the current like this.
Is it possible to uncouple the fan? if it is, then try the motor on it's own and see what the current looks like.
It would be very helpful if you can give us some background information.
Is this a new installation? has this operated before?
What is the voltage and frequency of the motor? what is the voltage and frequency of the supply? How is the motor being controlled?

It is possible that there is a problem in how the motor is connected (assuming that it is a new installation) or that there is a fault in the motor (if it has been running for a period and now failed) or a problem with the control equipment. (star delta locked in star)
There are many possibilities and we need a better picture in order to give you guidance.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[aolalde]

If the centrifugal fan is directly coupled to the motor shaft it is not under "no load" condition.

Uncouple the fan, if the high "no load" current persist,and it shows balanced on the three lines; the voltage is to high or the motor winding is wrong, could be the connection, the turns per coil, span, etc.

 

[BJC]

You may have a generator. There may be extraneous air currents turning the motor and generation power.
I have seen the it happen in paired containment ventallation fans. The fans were in parallel ducts. One fan would start and back draft damper in the other fan would let enough air through to spin the other fan backwards. It was generating enought reverse voltage and current that it would start. People were looking a brakes ( mechanical and electrical) VFDs and bigger overload sensors. The only proper fix was to fix the back-draft damper.

 

[badservo]

I agree with all of the above and just want to add that some motor/fan units will overload the motor without flow restriction on the inlet/outlet of the fan

 

[Wrongboy]

Thanks for all the answers. We rechecked some of our calcs and realized that the flow we were getting from the fan was high enough to acount for the amps being pulled. Thanks again for all the answers.