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Motor Rewind Question

Motor Rewind Question

Motor Rewind Question

(OP)
Had a 2000 HP 2300V 3600 RPM WP2 motor rewound say 4 months ago. Motor age is approximately 40 years old. The motor ran for 4 months after the rewind before it tripped due to a stator fault. Found that that the fault occurred from a finger that was holding the stator laminations had come loose. Is it unreasonable to consider that the rewind shop should have checked all fingers during the rewind? Considering that there are say maybe 1500 fingers on the stator holding the laminations together, is that reasonable?.

RE: Motor Rewind Question

As a rewinder, we check all electrical and mechanical aspects of stator (and rotor core) before rewind. The rewind shop is responsible for this.

Muthu
www.edison.co.in

RE: Motor Rewind Question

Did you perform the PI test before to start the motor?

RE: Motor Rewind Question

Yes, it is reasonable. I agree that the shop is responsible for the failure.

RE: Motor Rewind Question

40 years is no age! Do not understand "Finger" What came loose? I don't think that I have ever seen 1500 "Fingers" in a motor. Not one of the lamination teeth?

What guarantee does the winder shop have? A minimum of 12 months is common. Many have more.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Motor Rewind Question

Gunnar - Fingers are the I-shaped ventilation duct pieces which are spot welded to the teeth of the core lamination.

Muthu
www.edison.co.in

RE: Motor Rewind Question

Photos.

Pictures of the failure tell a story the written word cannot compete with.

Share some photos.

John

RE: Motor Rewind Question

Yes! Please

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Motor Rewind Question

(OP)
Close up pic of the missing finger

RE: Motor Rewind Question

Thanks a lot! We call them wings. Entirely my fault - lack of imagination...

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Motor Rewind Question

BTW are they really needed on a WRIM? Seem to impede air flow more than helping.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Motor Rewind Question

Are those through bars to hold the laminations tight together?
It looks as if there are spring clips to exert some pressure on the laminations.
I suspect that during the rewind this may have been used as a fulcrum for a prying tool and bent and damaged.
I see that one of the other fingers has been bent.

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

RE: Motor Rewind Question

We call them end pressure plate fingers which keep the cantilevered teeth compressed axially and prevents them from vibration due to magnetostriction and other forces. These pressure fingers are welded to solid annular end plates (we call them end pressure plates) located at both ends of the core stack and just below the slot/teeth bottom, which are axially pressed and locked during core building. A broken pressure finger will allow that tooth to vibrate and chafe the coil ground insulation leading to earth fault eventually.

Muthu
www.edison.co.in

RE: Motor Rewind Question

Is it okay if I'm a bit “nit picky” regarding the photo? (I know beggars can’t be choosy ; )

The picture fails to show the area of failure. Smoke charred coils are a result of a failure, but the photo
does not show where the so called “finger’ penetrated or caused the winding damage.
That's what the audience here needs to see.

I’m somewhat skeptical of a stator tooth support coming loose. I’ve seen lost screws in stators playing havoc,
and pieces from the rotating member coming apart causing a big mess, but stator teeth and their associated
components are very robust stationary items. They are hard enough to separate/fix during “hot spot” repairs.

Additionally, a stator that has been previously repaired more than once over its entire service life can be minus
all kinds of minute details that play little to no roll in their effective operation.
How does one know the so called loose part was even there to begin with?

It’s of course highly suspect that something occurred during the repair process that may have contributed
to the short lived winding repair. “But”, so far I don’t see the evidence to authenticate the theory.

Do you actually have the broken or separated tooth component in hand? What does that look like?

John

RE: Motor Rewind Question

I seem to remember a previous picture that showed the damaged finger but not the damaged winding.
As a suggestion:
The pre-wound coil was a little to narrow.
A tool was used to spread the coil slightly to place it in the slot.
The finger was used as a fulcrum for the prying tool.
The finger was bent or broken at that time.
Because the coil was slightly too narrow, there was more than normal pressure against the side of the slot.
A combination of the vibration of the unrestrained end lamination and the side pressure of the coil led to the failure of the coil.
Near the edge of the picture we see a bent finger, bent in a direction consistent with being used as a fulcrum. I believe that this supports my theory of narrow coils and pressure applied to the fingers during assembly.

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

RE: Motor Rewind Question

I think that repair shop after rewinding *forgot* to additionally pour the coils with insulating varnish,VPI process and furnace treatment.
It seems a very bad work if after only 4 months the winding head looks like this .
Good luck

RE: Motor Rewind Question

Not all motors are necessarily VPI processed. Non-VPI resin rich process, which predates VPI, is still widely used. The old winding was most likely non-VPI and it worked fine for 40 years.

Muthu
www.edison.co.in

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