Tsunami hit generators' refurbishment 9

[edison123]

In the recent havoc wreaked by tsunami in a remote island off Indian Ocean, 4 nos. 11 KV, 5 MW diesel generators were submerged under water up to the bearing level. The generators are semi-open (with ventilation filters fixed to the end plates) and have VPI windings.

I have been asked to visit the site and advise the course of action to bring the units back to service since this is the main power plant in that island, which needs the power badly for the relief operations. I am doing this pro bono.

Any quick & dirty remedial measures/suggestions/tests will be much appreciated.

 

[karlbamforth]

Hi,
I am an aircraft engineer rather than an electrician.
Strangely I have come across a number of electrical motors that had been submerged in water, one for over 2 weeks.
I flushed them with clear water, sprayed water repellent on any circuit boards, ensured the brushes and comutator were clean. Made sure it was completely dry and clean, lubed the bearings if they were not sealed, then run them up.
Never had a problem with them. The one that had been submereged for two weeks was still running at least two years later.
As I say I'm an aircraft engineer so this info should only be used for emergency measures not a long term guarranteed fix.
Hope it helps.
Karl.

 

[Marke]

Hi Edison

The major problem that you are going to have is that the water was not clean and would have been very salty.
I likewise have serviced quite a lot of equipment that has been under water for days due to river flooding, and the secret has been to thoroughly dry out and then used compressed air to remove the silt deposits. Any metal parts that are not treated, coated or protected need to be cleaned and coated to prevent corrosion.

I suspect that in this case, you will have salt deposits all through the machines and the difficulty will be to get these out.

My personal approach would be to thoroughly flush out with clean water to remove all the salt deposits and this will be a major challenge. Once you are confident that any salt deposits are removed, it would be a case of thoroughly drying out and coating all uncoated surfaces after carefully looking for visible signs of corosion. Strictly speaking, the windings should be varnished etc and should be relatively impervious to moisture, but we no that is never the case. The biggest problem I see is where corosion has already begun in critical regions.
The first thing to do when electrical/electronic items get immersted in salt water is to put them into clean fresh water and keep them immersed until you can dismantle wash and dry.
Sounds like a real challenge.
Good luck

Mark Empson

http://www.lmphotonics.com

 

[busbar]

 
For ancillary equipment, there is a US-NEMA guide PDF available for download regarding restoration of water-damaged gear [free with qualification.]

http://www.nema.org/stds/water-damaged.cfm

Best to you, edison123.

 

[Skogsgurra]

I admire your undertaking. It is good to know that there's energy and willingness left in the world.

I have had electrical equipment that was flooded with dirty water from the room above when the sprinkler system went berserk. There was dirt and concrete dust and what have you mixed with the water.

The equipment was cleaned by a professional company and operation resumed. Then, during spring, there were several failures. The equipment exploded more or less. I knew nothing about the water damage and was asked to find out if there were any transients on the grid. I found nothing, but I found flash-overs that indicated high voltage. At last, someone told me about the water and I started to look for damages. I finally found dirt inside insulating sleeves and there were traces of flash-overs which had propagated outside the insulator.

This rather long story is to tell that even professional companies with the best equipment and ideal working conditions can fail if done in a hurry. Be prepared that the work will take long time. And good luck!

 

[busbar]

 
edison123 — terse {4½ page ~30KB} excerpts of the NEMA “water damage” text…

http://www.6L6.net/waterdamaged-electricgear.nema.doc

http://www.6L6.net/waterdamaged-electricgear.nema.htm

http://www.6L6.net/waterdamaged-electricgear.nema.rtf

 

[electricpete]

busbar contacted me about a reference from IEEE-1974 which discusses drying of motors/generators (was deleted in IEEE43-2000). I direct emailed a relevant excerpt from IEEE43-1974. Let me know if you didn't get it.

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[MikeHalloran]

Bring your own food and drinking water.

You cannot assume availability of clean fresh water for rinsing. Inquire if they need you to bring a well point and a jet pump, or whatever else they'll need to get rinse water.

Also inquire if they have a few gallons of Brakleen or similar no-residue solvent, for cleaning insulators.












Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[edison123]

Thank you guys. I knew this is the right place for the right solutions.

I have been told that there is limited crane (5t) capacity as well as space. My first (& probably biggest challenge) is to disassemble and reassemble. And then, the corrosion of laminations due to salt water. Time (as always) is the no. one enemy.

I am leaving to site shortly and will keep you posted on how it goes. In my absence, I have asked my brother to keep tab in this thread. He will pass on the further posts to me by mobile (which is indeed a god send in a situation like this).

Thx again for your time & advice.

Kumar

 

[electricpete]

I'm not sure if you got it so I'll recap the highlights from IEEE43-1974:

Heat by current or external heaters. [Note I have done drying by current before and you need far less KVA to heat by dc welding machine than by ac welding machine. The reason of course it requires a lot of voltage to force the ac current through the winding inductance, but not so for the dc.]

Heat to no more than 90C by winding RTD or 80C by thermometer. Higher temperatures will accelerate drying, but should be made with caution and consultation with machine manufacturer.

Avoid increasing temp by more than 5C per hour to avoid damage to insulation by gas or vapor formation.

Monitor dryout by P.I. Stable high P.I. indicates dryout is complete. If monitoring by resistance, the effect of temperature correction error is large. Uncorrected temperature will initially decrease upon heating due to increase in temperutare, than increase as winding dries out.

One decision you have to make is to dry immediately or remove for steam clean, then dry. For max reliability the first option but obviously your situation time may dictate the 2nd option. Since you have VPI probably it is less risky than it would be for B-stage windings.

Have you given thought to the bearings? I would not be surprised if they have been flooded even a short time to see rust. My gut feel is that rusting of the stator is not as big a concern. Our motor repair shop actually puts stators in salt water on purpose to improve core lamination perforamcne. So I don't think it causes hot spot but might possibly lead to longer term loosening of the core.





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[electricpete]

"My gut feel is that rusting of the stator is not as big a concern. Our motor repair shop actually puts stators in salt water on purpose to improve core lamination perforamcne."

I was talking there about stator core, not stator.

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[electricpete]

Two more references on winding drying which I also sent by email:

1 -

http://www.usbr.gov/power/data/fist/fist3_4/vol3-4.pdf

pages 8-10.

2 - Doble Proceedings 1999 "DRYING METHODS FOR ROTATING MACHINE WINDINGS"

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[Laplacian]

You can flow compressed nitrogen across the windings also to dry them out.

 

[edison123]

Feedback on my inspection of the station :

Sea water had entered into all four generators up to the bearing level. Inspection of the insides revealed mud and oily slime on the end windings. Back iron of the core (OD) has started rusting. Though the insides of core is not visible, I am sure core also has mud and grime.

This is a non-vpi machine. What would be your advice to refurbish them (especially the salt deposit inside the core between the coils and the slot walls) ? If I use clean water to hose down the core + windings, will the salt deposit go away ? How will water hosing affect the stress grading paints on the coils ? How will the core be affected by wash down ? What would be the recommended tests to ensure the integrity of the stator and rotor windings ?

The government needs these machines urgently since this station used to meet 90% of the island’s load. All the relief operations are affected due to power shortage. Now, they have revived a very old station (not hit by tsunami) and are meeting about 30% of power requirement. Black outs and load shedding are quite common.

Your valued suggestions to bring the units back on line will be highly appreciated in these critical times.

Control and protection panels are also damaged and they are being revived by OEM's on war footing. Strutural damages are also being attended to.

 

[electricpete]

One philosophical comment: I would say clean as best as you can and then DON'T do a hi-pot or surge test. The purpose of a hi-pot might be viewed as forcing a failure since it is in most cases better to fail during test than to fail later during operation. But in your case desperate for power, failing now or failing later equally bad since both require rewind. BUT we can minimize probability of failure by not doing any hi-pot.

It may be likely your stress grading paint at the slot exit will be damaged from mechanical or chemical action and you can therefore expect high partial discharge when you put the machine in service. But partial discharge at slot exit is a long-term degradation mechanism (years for 13.2kv machine) and probably not a concern here (plan for possible rewind down the road when generator is not critical).

One of the biggest concern for short term machine reliability would seem to be if the salt deposits have penetrated into the groundwall insulation. I don't think any amount of cleaning could remove if it it's there. But all the more important to perform very complete drying (salt with moisture probably many times worse than salt alone) and avoid hipot at all costs.

The core rust once again I think you clean what you can but remember rust is an insulator and shouldn't cause a hot spot.

Your options for cleaning:
1 - leave rotor in place and clean what is accessible.
2 - pull rotor and clean stator in place.
3 - pull the whole machine rotor and stator out for shop cleaning.

1 probably not good enough and 2 would seem to be minimum. 3 obviously the best if time allows.

I am quick to throw around my opinion but I don't have nearly as much experience as yourself so take it with a grain of.... salt.

Good luck. We all wish you success and I'm sure many people are thankful for your efforts.

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[edison123]

Thx pete. I have also ruled out any HV/surge/tan delta test. Given the circumstances, I would rahter take the risk of m/c failing in service than during test.

I plan to dismantle the generators at site. But special rigging have to be made since in the EPC contractor's wisdom, to cut costs in a multi million dollar plant, they have provided a 5 ton crane when these beasts weigh 30 tons.

A grain of salt - that's a good one.

Kumar

 

[Laplacian]

If you use water to clean the mineral deposits out of the windings; use distilled water or demineralized water. It will absorb the contamination better.

 

[electricpete]

I'm sure you are also familiar with cleaning by Walnut shells, corn cob blast etc which provide mild abrasive. Also lately here we have heard that dry ice blasting is a very effective stator cleaning method (with the exception of oil which it does not remove very well). Dry ice provides the same mild abrasive as the others but the particles disappear when they turn from solid into vapor, leaving no contaminants introduced by the cleaning.

The service is provided here in US by a truck that comes to your facility for in-place cleaning. I don't know about the logistics of getting that service onto that Island... I'm sure it would be challenging.

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[BJC]

edison123

Here's one from Square-D.

http://ecatalog.squared.com/pubs/Automation Products/0110DB0401.pdf

I have been looking for some papers I had from an old GE course on maintence. It may have had something on flooded equipment.
I suspect some of the answers your getting here may assume you have equipment and facilites that you could only wish for. I suspect your stuck with "Stone knives and Bearskins" so to speak.

There are two forums here that you should post your question to.
They are the
"Marine/Ocean engineering other topics Forum" and
"Dock & marine facilities engineering Forum".
You need someone with navy and merchant marine experience. There is more than one old electrican's mate out there who has done what you need to do. I worked with a guy who could fix your generators ( he in fact did a similar job once on board a submarine, however he's not with us any longer).
There is also a google news group "sci.military.naval" where I sure you will get some response.

 

[ruggedscot]

Best of luck with this one and my thoughts are with you.

This disaster has been so bad and well you can see peoples desire to help and assist. Good on you and hope that you manage to get the units up and running.

If you do then Ill raise a glass to you.

Rugged