Motor Failure 4

[VTer]

All,
Please see attached photo and let me know if you can identify the root cause of the failure.
Motor data is: 10HP, 460V 3-ph RPM 1755 with Class F insulation


"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[electricpete]

Also, I don't know if it's typical to burn out the winding for random wound, but obviously you don't want to burn the winding out if you hope to recover useful info from the slot section.

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(2B)+(2B)' ?

 

[dArsonval]

jraef (Electrical) Hits it on the Mark!

"Looks like you had the rotor crash into the stator, then you have winding damage."

This is a Rolled Steel-Frame Motor Winding Failure due to undo mechanical stress.

The rotor clearly rubbed the stator winding... causing heat, and an inevitable insulation failure.

A motor like this is typically thrown away... and a new one is installed in-place of it.

John

 

[electricpete]

People look at things different ways. That’s why it’s always a good benefit to have a lot of people chiming in different ideas.

My thoughts: You can see huge depth of the liner below the bore. Looks like at least 1 / 4” and maybe more. I think if there was a rub, it definitely didn’t wear through that distance all the way to the coil (the depth difference between bore and liner still looks visible all around the top and bottom even after the fault).

Maybe you’re saying the rub caused stator core eddy current heating... leading to coil failure... wouldn’t that cause ground fault (which would deprive the ability of the coil to cook)?

To me it seems much more likely the fault started as turn to turn fault. It heated the whole coil between the time the turn fault initiated and became ground fault. The slot liner for both slots of that coil deformed from the heat (crinkled, buckled, whatever) and went into the gap producing debris downstream of those slots. The rest is soot. That’s my guess (along with Ray and Mark similar comments).

But you never know. The guy standing there looking at rotor and stator has a lot better view than us. It shouldn’t be hard for him to check if it’s a rub or not. Eventually as the focus shifts to rewind options there may be a core loss test which would give additional info about presence/severity of any rub.


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(2B)+(2B)' ?

 

[VTer]

The rotor did not hit the stator. The marks are from melted insulation coming through the slots onto the rotor. There could have been some minor vibration due to bearings but my best guess would be that this was a turn-to-turn fault that escalated very quickly. I also did notice some rusting on the shaft, and I think this is because the motor drove a blower which was part of the cooling unit with humidification system built-in. I think a combination of age, belt dust preventing proper air circulation, and humidity exposure finally took its toll on this stator. I do not think that we could have done much as far as electrical protection to minimize the extent of the damage on this failure. The overloads were sized correctly and I do not think that even GFP would have caught this type of failure much sooner than the overload? My other question to the manufacturer of the cooling unit is to find out why they did not use a totally enclosed motor to help with belt dust contamination.

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[KllrWolf]

I would agree with the turn to turn fault. The pictures of the stator do not show any signs of rotor contacting the stator enough to overload a winding. With rotor to stator contact that great, you would expect to see deformation in the teeth, if not parts of the teeth broken off. The majority of the marks on the stator appear to be material smearing. With a single phase fault, you would see the opposite (in this winding configuration) coils burned as well, which without pictures of, would assume they are not.

 

[Sparweb]

VTer,
Have you done any tests, even just with a multimeter? Resistance from wire to case, phase to phase? I figure there's a short somewhere, too, but of course finding it is important if you think the motor is worth saving. In the end, if it's cheaper to re-wind than buy a new motor, then re-wind everything with new wire. If so, there isn't much practical need for a root cause analysis (IMHO). In fact, the process of removing the wire (before re-winding) is the only way I can think of to actually see the insulation fault (if there is one). The re-wind shop may try a few tests of their own (growler) if you ask them to, but it won't change the fact that the motor is either scrap or needs repair.

PS If your company opts to buy a new motor, ask if you can keep that one (if you're looking for a hobby )


STF

 

[Motorwinder]

I still say a grounded coil. When you strip it look for copper melted in the slot.

 

[dArsonval]

What information relates to the mechanical aspects of this failure?
(I realize the motor in this topic has likely been replaced/re-installed and is hopefully back in service.)

Questions continue to stir the pot. And they should.

What do/did the bearing "fits" reveal after inspection?

What are the actual dimensions of the end bracket housings?

And the rotor journals... as well?

Look how "BROWN" the bearing pocket/housing "is" in the photo submitted at:

http://files.engineering.com/downlo...508-4ddd-9c32-a1cc8459a3cc&file=close-up1.JPG

This motor had excessive mechanical stresses upon it contributing to its electrical failure.

John

Always enjoying this forum.