3 phase motor help please

[Hotrod56]

I was taking apart this 1940's 3 phase motor and screwed it up. The fan damaged the stator windings and I would like to know if it's fixable. Can I just separate the wires with an Exacto and then add some insulator fluid? I am sure it's not that simple.

not that simple and if it is possible, is there a product that I should use?

Thanks in advance for your help.

 

[itsmoked]

Hotrod, is that all one spot of damage? Or is that three one areas of damage?

I know how I'd fix that but I'm thinking there are more experienced motor doctors here. If they don't show I'll chime back in.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

How deep are the cuts in the wires?
Many years ago,I saw a 40 HP, 3500 RPM motor damaged by a breaking fan.
There were numerous cuts about 30% to about 40% of the way through the wires.
The maintenance chief directed the electricians to do as you suggested.
The windings were coated with Glyptol.
He justified the repair this:
While the damaged portions of the windings will run hotter, the surface of the end turns is much better to disipate the heat than, for instance, the windings in the stator slots.
THere were two similar motors on the machine.
This motor had a lower load factor than the other motor.

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

 

[Hotrod56]

Thanks for the responses. There are several areas (5) of insulation breach.

 

[Hotrod56]

Question - If I attempt to do this - separate the bad wires and coat with Glyptol, and I don't get it right, what will happen when I try to run the motor? Will it just smoke and be done? Thanks

 

[BrianPetersen]

If you have continuity through all windings (should be easy to check with a meter)
and none of the windings show out-of-bounds high resistance (check with meter ...)
and you are careful to not introduce any cross-circuits between windings (be careful, visually inspect)
and the stuff that you use to re-insulate the windings is the right stuff and properly applied so that it doesn't break down with vibration and heat ...

... the motor will work fine. Maybe don't load it all the way up to max rated load or allow excessive starting current from a high-inertia load.

Worst thing that happens is that it says "bang" and the smoke comes out.

What does the application have in terms of circuit and thermal protection?

 

[Palletjack]

One of those wires completely into or do I need new glasses?

 

[jraef]

On an 80 year old motor like that, each individual strand of "magnet wire" has a clear enamel insulation coating, then the strands are "turned" into bundles called "coils" with each bundle forming a coil has a varnish coating overt them, then another varnish coating over the entire assembly. Glyptol is that varnish coating, it is not the actual enamel insulation of the magnet wires. You will have a very difficult time separating the individual strands from their coil bundles without damaging the enamel insulation of the adjacent wires. But if you do manage it without cutting a strand (assuming none are fully cut already), you might be able to get away with repairing it in situ. Worst case scenario there is that some of the turns are shorted together in the process, making the effective turn ratio less than what the motor was designed for and thus causing that coil to draw more current to make the required torque, hastening the demise of the rest of the motor. How much extra heat and how fast that affects the motor is highly variable, from almost no noticeable effect to it burning up in minutes.

But if a strand is broken, you can end up with discontinuity in a coil, which makes the entire coil open circuit and basically dead. That then creates a sever imbalance and the motor will not really function correctly.

But here's the thing; you have it, it's already damaged, you might as well try, because the only alternative is to have it rewound now, which is still an option after you try it too.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[waross]

A megger test is almost useless in determining turn to turn shorts.
Turn to turn shorts are the biggest issue here, but not the only issue.
Another possibility is a turn cut completely through.
Again, not something usually tested for or found during a normal megger test.
A turn to turn short will often lead to rapid escalation and motor burn-out.

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

 

[Hotrod56]

It will be hooked up to a phase converter.

I appreciate everyone's knowledge.

 

[waross]

What will the motor be driving?

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

 

[Hotrod56]

It is from a disc sander. Porter-Cable

D1 Disc Sander.

 

[dArsonval]

The winding can be repaired using a heat gun, tweezers, a screwdriver, sand paper, random lengths of the correct size magnet wire,
a soldering gun, and misc insulation / sleeving.

And anything else required to get the job done.

To make such a repair in today's day-n-age would be what's known as a band-aid approach.

It would also take the knowledge of someone having patience, and a tedious knack for resourcefulness during the job.

How long would it take to repair? As long as it takes.
How much would it cost? As much as it does.

The best way to fix this [problem] is to drop it off at a competent motor repair facility,
and have them completely rewind the stator.

Completely dismount the stator from the mounting plate, disconnect the conduit wiring, etc.

Leaving the connection box fastened to the stator is optional, the winder will end up removing
it anyway.

Among some of the details a competent winder would adhere to is noting the dimensional height
of the windings protruding from the laminations at each end to accommodate clearances for any internal rotating parts.

For what this is, the stator could be completely re-wound in a morning's time, in the oven to bake by afternoon,
and returned to the customer the following morning.

The item could be "quick cured" as well meaning if the job was started by 7 AM, it could be
back to the customer by mid afternoon EASILY!

John

 

[Hotrod56]

dArsonval, thanks for the detailed explanation. Sounds like a lot of work.

 

[electricpete]

John works in a repair shop and has been there for a long time as far as I can tell. Seems like good advice. I'll just add my two cents as the plant motor guy (not the shop motor guy), mostly repeating his theme:

Rewind is sort of a commodity type job which is commonplace and can be done efficiently in a standard manner.

Repairs attempted on random wound coil endturns would be an unusual and non-standard thing to attempt, very skill dependent and you don't really know if you can make it work until you're done. For one thing you have to heat enough to melt / soften enough of that resin hunk to be able to pull out enough length of the strand at each end to splice onto. How much heat will that take... no idea until you get there. Will the nearby strand enamel be damaged by the heat and mechanical movement.... no idea until you get there.

Just thinking through what might be done (which spoiler alert ends up as a dead end): We have on occasion done coil cutout repair on a larger form-wound machine. Basically you take an entire damaged diamond coil out of the circuit, jumper around it and just live with the resulting imbalances and derating. But you have only a few strands to work with on form wound coils, whereas you have a lot more on random wound so I'm not sure that type repair would ever make sense on a random wound machine (maybe John knows). And on this particular machine you'd still have to deal with that thick resin to be able to make coil connections. And on this particular machine you have multiple coils damaged to boot. You're going to need a winder to do it, and it'd probably take him a lot longer to figure all that out than to just rewind the darned thing.


=====================================
(2B)+(2B)' ?

 

[waross]

The only downside to a rewind is the cost.
I expect that a rewind on a motor of that size will be more than a new motor, if a new motor is available.
The motor is not usable as is.
If the wires are not cut more than half way, they will probably carry the current without overheating.
Compare the ability to reject heat from the surface of an end turn with the ability to reject heat from deep within the stator.
I suggest making sure that there is no turn to turn contact and then a coat of glyptol.
It will probably be serviceable for a long time.
A couple of hours and a couple of dollars.
If the quick repair fails, you are left with what you started with, an unserviceable motor.
That is the time to consider rewind or replace.
I have seen similar damage successfully repaired with Glyptal.
That was a 40 HP motor on an industrial planer running 16 hours a day.
The boards went through end to end with no gap between boards.

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

 

[Hotrod56]

Thank you everyone for all the responses. What a great place to go (this website) where there are so many with so much knowledge. I sure appreciate it all.

 

[itsmoked]

I like Bill's thinking. (too bad about him)


LOL

I'd reassemble it as it sits and turn it on. If it runs leave it running for an hour looking for any thermal follow-on issues.

Pull it apart and slather this on the booboos. Works exceptionally well.

Red Goo

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Hotrod56]

Got nothing to lose. Thanks

 

[waross]

(too bad about him)

What?
Did I die and miss the memo?
Is loss of short term memory involved?
Grin.

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