A/C Induction Motor Run-in 1

[jdogg05]

I understand that it is necessary to perform a run-in on brushed D/C motors because the brushes have direct contact with the shafts and this could affect alignment. Is it necessary to perform run-ins on A/C induction motors? The stator and windings don't actually touch the shaft. The only thing it might affect is how the bearings are seated... But could this really change that much (enough to affect the alignment)? I am discussing this in the context of industrial plants where the pump drivers are almost always A/C induction motors. In essence, how important is it to perform a run-in on an induction motor prior to final alignment?

Thanks for any help!

 

[desertfox]

Hi
I have never known a run in on a pump motor set, what you need is to get hold of the suppliers installation manual, then if there is a requirement to run in it will be detailed in there.

 

[jdogg05]

Would you not do a run-in to find magnetic center?

 

[desertfox]

Hi

Have a read of this alignment installation

http://www.plantservices.com/assets...sets/A_Practical_Guide_to_Shaft_Alignment.pdf

 

[LionelHutz]

I've never heard of performing a run-in (break-in) on any motor. Running it to determine the magnetic center isn't the same thing and really only applies to motors which require the coupler to maintain runout.

 

[jdogg05]

OK thank you for your input. I am red-lining a rotating equipment installation procedure and the previous person put a comment in the "Final Alignment" section:

"Motor run-ins shall be performed prior to the start of final alignment activities. If final alignment precedes the motor run in, the alignment shall be rechecked after the motor run-in has been completed."

The comment made no sense to me because the manufacturer would already have run the motor during Factory Acceptance Tests...

I was just wondering what they could possibly mean by this. After doing some reading it seems that a motor run-in is only really done on a brushed D/C motor that has never been run before...

 

[jraef]

Most likely a remnant of an older DC motor spec. That's the only place I have ever seen it mentioned, and even then not for a looooong time.

Then again, it's been a long time since I've looked at any new DC motor installation...

"Will work for (the memory of) salami"

 

[electricpete]

I understand that it is necessary to perform a run-in on brushed D/C motors because the brushes have direct contact with the shafts and this could affect alignment.

A small detour for my benefit.
Can you explain what you mean by that?
I've heard of run-in of dc motors to help the brushes to conform to the radius-of-curvature of the commutator (see another current thread on dc motors). But I don't see how it relates to alignment.

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(2B)+(2B)' ?

 

[electricpete]

Maybe I got alittle confused in my last post... garnet paper with manual rotation to help set the brushes. Run-in to help with the film followed by inspection. But still no connection to alignment that I can see.

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(2B)+(2B)' ?

 

[MikeHalloran]

An AC motor needs a rotation direction check, then a smoke check.
Then just run it.

Checking (and recording) the bearing temperatures occasionally during the first days of service is probably a good idea, more so for very expensive motors. ... but then for very expensive motors you'd have bearing temperature monitors installed and connected to alarms or shutdowns, wouldn't you?







Mike Halloran
Pembroke Pines, FL, USA

 

[Skogsgurra]

Rather OT, but still pertaining to AC motors and brushes:

I visited a plant with large screw compressors some time ago. EDM problems. The motor manufacturer had put a shaft grounding brush on NDE and placed it close to the bearing. So close that the grease migrated along the shaft and eventually isolated the brush from the steel surface.

There, the same discussion regarding run-in of the motor was going on and the shop was divided into two "parties" - the run-in-sympathizers and the anti-run-inners. They were ridiculing each other and nothing had been done to remedy the problem. They created a mind-block from a misconception and while they were discussing that non-issue, the bearing failed.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[jdogg05]

API 686 has this paragraph:

"5.4.1.2.3 Axial alignment shall be done after the motor magnetic center is marked during field or factory run-in. The motor shaft shall be located on magnetic center. If the motor cannot be run for magnetic center due to an end fan, the motor manufacturer must specify the shaft position."

Which is implying that mag center is found by doing a "run-in"... Maybe the ppl who wrote that paragraph had a little screw up?

 

[LionelHutz]

"Motor run-ins shall be performed prior to the start of final alignment activities. If final alignment precedes the motor run in, the alignment shall be rechecked after the motor run-in has been completed."

Sounds like the customer just wants to see some hours on it without anything bad happening. It sounds like you are to align the motor and load, run it for a certain length of time (is the time specified?) and then align it again.

 

[JadeYork]

The brushes do make contact with the commutator on a DC motor which is usually pressed onto the armature shaft. The run in is not necessarily for alignment purposes but to make sure the brushes are correctly seated against the commutator. If the brushes are not seated correctly, arcing will occur causing pits on the copper segments of the comm.

In most AC motors you will have a bearing that is locked in an endbell (PE or OPE) and the opposite may have a spring washer to take up the endplay slop. If you are not using a rigid coupling you have to be sure to check and make sure there is enough clearance between the coupling halves. You do not want the halves to touch or you will run into issues with vibration and could possibly lead to axial pressure bearing damage.

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