Stator Winding of Generator Burn Out

These might not apply to your case, but long-idled electrical equipment can be infested with insects, cobwebs, animals or their nests, fungi, etc. These can create conductive paths resulting in arcing, which can in turn escalate into serious damage.

thats a short! any of the things Tornado mentioned or an impact to the windings, anything that gave a pathway for current to travel

Looks, to me, like impact damage caused a short circuit.

Forensic analysis of any failure can be a tedious process. Very often initial conclusions are found to be wrong once a complete tear down and methodical analysis is performed.

Generally speaking putting outside influences aside, this is caused from degradation of the winding coating, which is caused by environmental influences and everyday wear and tear.....that is why the maintenance on these includes a megohmmeter test at regular intervals, and the occasional tear town and redip of the windings...

Based on my half vast experience with coatings and the effect of heat degradation, I agree with you.

All insulating coatings get old and brittle over time. Heat speeds the process. Excess heat speeds the process up excessively.

Insulation resistance testing - Test Equipment Depot

This machine was be rewinded the stator winding one year ago.

we used VPI (vacuum pressure impregnation) for this machine.

Perhaps a mistake made during rewinding? Or too much load on that winding part- If phase controlled equipment is used as load, it might compromise that part. We have here a monster machine (stepping dragline) that "clips" part of the phase when overloaded. We can see that all over the grid. It is like a certain angle shortcut.

If the picture is orientated correctly I would suspect a build up of debris weakening the insulation.

Is the generator used as a standby? Neglect becomes a big problem.

it's not used as standby.

it's used all the time.

one year after rewinding. it's burn out

Get back to the re-winder, and get a repair done under the warranty arrangements.

**below picture is rotor**

The machine is Frequency converter (50hz to 60hz) which have 2 synchronous machine coupling together (mono-shaft).

one machine is the motor

and another one is generator which burn out.

Perhaps it was struck by lightning....more likely an oversight during rewinding process though....What triggered the original rewinding? Perhaps there are harsh environmental forces at work here? Any corrosive use in the area? What was the thickness of the winding coating? and what type of coating was used? Is it protected from rain and wind?

All of the answers are valid and lightning is a potential candidate. There is a newer type starting to be recognized as "ground lightening". That type originates miles away from a conventional strike, but may travel to another point at several feet above the ground for a distance of several miles. If you decide to investigate lightening as a potential cause, check for surrounding strikes as much as a week before that could have caused damage to the controls.

lightening ≠ lightning

The actual cause which triggered the failure is open to conjecture as many factors could have been present.

What concerns me is now that the machine has suffered two failures some twelve months apart then I would suspect that the "iron" or laminations of the unit may also now be damaged which would cause degradation of the magnetic flux paths, which in turn will cause localised hot spots exacerbated if unit is overloaded.

Your repairer should be able to perform electro magnetic tests to confirm that the lamination stacks are OK

The first issue I would inspect is why or where is the isolation Barrier between the windings. This is suspect to me, because it seems to have started between where the windings are closest.

Another question I need to ask; Is there a mid-ship bearing between the two sets of windings?

No, it's not have.

it is single shaft.

Is this not a classic case of unbalanced loading resulting in negative phase sequence currents and resultant damage to rotor and stator, I wonder.

Well, to state the obvious, more current was demanded than the windings were capable of carrying without overheating. Have you checked your over current protection devices?

Martin

If it's close to the ocean, salt in the air can accumulate on surfaces and draw moisture out of the air forming a conductive path.

Looks like it was over loaded, which would have caused the amperage to rise. Was a heavier load installed this year? Was it made to to heavier work than usual? Please check the circuit breakers and if any, the fuse links. Often, during re-winding, they sort of forget to install fuse links.

This would be very expensive to rewind, my heart goes out to you!

-----------my final comment on this thread--------------

I still think the windings took an impact, at least a good chance of it. the comments about degraded varnish/insulation are valid points for an aged motor but all that would have be disregarded when the unit was rewound. I don't think age and heat accelerated insulation this rapidly.

the quality of the rewind is certainly in question as well as the quality control of the testing procedure performed (I'm assuming it was completely tested before being returned to online service) a motor this size typically has some type of over-current protection. clearly it failed. if the overloads test as good and there is no information that supports an impact (like a dropped wrench or endbell against the windings, and after all voltage checks have been performed(imbalances, phasing etc) I would be contacting my rewinder and seeking warranty. good luck

Hello Cr4 people

Mister Soolloos

most of the replies are helpful.

I think,by installing the rewound rotor or stator, you should check the balancing of the rotor and the bolts that fastened well.

During the continuous working, vibration and heat, and the bolts might elongate.

there is a device which measure the vibration, it should be performed every period after the rewound.

Long ago, I was testing a generator that was coming back from a rent offshore. I hooked the unit up to the load bank and started the engine. let the engine warm up and flipped the exciter switch BOOM. The engine was brought down to its knees and the end of my finger was black from the fire that came out of the switch. After I cleaned my pants, I inspected the generator for what happened. It looked about as bad as yours. Turns out, the generator had salt in it.

Look at the rest of the stator winding and see if there is any small green areas. The copper while turn green when exposed to the air.