drying transformers

[bb55fixr]

Hello all. I work on a World War 2 era battleship memorial. We had a sizable leak and on of our general lighting transformer banks got wet about 2 inches up. They are three individual single phase 440/120 20 KW transformers wired in a delta configuration. It blew the A and C phase 100 amp primary fuses, the B didn't blow. We are drying them out with heaters and the megger readings from phase to ground are all over 275 on the 1000 VDC scale and rising. The phase to phase readings are 1.2 on A, 0.1 on B, and 1.3 on C, all on the 250 VDC scale for more accuracy. Has anyone ever dealt with such a circumstance? Does it just take a lot of time and heat to dry out water trapped between the windings? Is there anything we should do other than applying heat? Any other suggestions would be welcome.

Thank you very much.
Terry Kuhn
Maintenance Supervisor
USS North Carolina Memorial

 

[Jraef]

I posted this in another forum after Katrina, most of the links still work.

 

[broadgage]

If enough fault current passed to blow 100 amp fuses on the primary side, then this may suggest that significant damage has been done and that replacement/rewinding may be the only option.
To promptly blow a 100 amp fuse takes several hundred amps, which can easily melt winding wire or burn away insulation.
If the fault current was only about 150 amps, then the fuses would have passed this for some time, likely resulting in burnt insulation.

The traditional way to dry out a transformer is to short circuit the LV windings, whilst energising the HV windings at a very much reduced voltage.
The reduced voltage should be adjusted such that about the normall full load current flows. The resistance losses in the windings will heat them, and dry from within, more effective than heat supplied externaly.
The voltage on the HV windings will be a few % of the normall.
(I have used 440 volts applied to an 11KV transformer)

This technique is however normally applied to transformers that have become damp in transit or storeage, not immeresed in water.

There is a lot to be said for replacement, even if it works after drying, I would not trust it not to go bang, probably at some inconvieient time.

 

[bb55fixr]

Thanks for the advice. I think we will continue drying and use the idea of putting low voltage to the primaries/shorting the secondaries. We thought of doing it but were afraid there might be something that we were overlooking by doing that. We hope that since they built these for the Navy and they built them 70 years ago when everything was built quality and overkill that they might dry out okay. All of the links pretty much say to replace them, that a dry air transformer should be replaced after immersion. So,we are also looking for an unused bank on the ship we can swap if they don't make it. I'll write back sometime next year to let you know how it goes.

Once again, thanks for the good advice and quick replies.
Terry

 

[LarryFine]

The traditional way to dry out a transformer is to short circuit the LV windings, whilst energising the HV windings at a very much reduced voltage ... adjusted such that about the normall full load current flows.

I suggest a Variac as the source, adjusting the voltage while measuring the current with a clamp-on ammeter.

 

[iceworm]

The traditional way to dry out a transformer is to short circuit the LV windings, whilst energising the HV windings at a very much reduced voltage.

The reduced voltage should be adjusted such that about the normall full load current flows. .

This is a method I have used as well. For the size xfm you are dealing with (Primary FLA of 40A or so), I'd suggest using an AC welding machine. Get a big enough machine that you are not exceding the duty cycle. You will be several hours.

ice

 

[BJ Conner]

Transformers

Transformers

Are these original BB55 transformers?
You can apply dc current to the windings with a welder. It has to be on that allows good current control at low currents. Don't get the one off the farm.

Heat is good but a vacuume is better. IF you can find or build a vaccume chamber and keep the internal heat on it may be the best you can do.
If you can get a TTR test set it can tell you if you have a shorter winding ( I think - I have never done it to a transformer that small)

 

[iceworm]

You can apply dc current to the windings with a welder. It has to be on that allows good current control at low currents. Don't get the one off the farm.

One can use DC, but that doesn't put current through both windings. An AC welder will hit both windings.

ice

 

[bb55fixr]

Thanks, didn't think of the welder. Pretty cool. We have a very nice Hobart we can use. Yes, these are some of the original transformers installed around 1939. Would really like to save them.

Terry

 

[jumper]

Hello all. I work on a World War 2 era battleship memorial.

Wow. That is totally cool.

 

[skeshesh]

Yea sounds cool. Can we see some pictures please?

 

[BJ Conner]

Yea sounds cool. Can we see some pictures please?

Ther's a few pictures here.

http://www.battleshipnc.com/

It's a stop for me the next time I am in that part of the world.

 

[brian john]

Prior to blowing the fuses, you had a chance, I have meggered transformers and had ")" megohm readings after drying had readings exceeding 2000 megohms. One in particular was completly under water and is still in use today 20 years later.

But it takes quite a while to dry one out, most likely not the best idea, but in soome circumstances necessary.

What we usually do, is use a heater, de-humidifier and a variac

 

[K8MHZ]

Ther's a few pictures here.

http://www.battleshipnc.com/

It's a stop for me the next time I am in that part of the world.

There is a ham radio station on that ship. I may have a contact with her in my log as I have worked several battle ship stations.

http://www.ac4rc.org/battleship/battleship.html

We have one on the USS Silversides and the LST 393.

If you go to the LST link you will see a picture of the radio men. I have actually operated amateur radio from the very desk in the picture. Some of the old rados are still there. We are in the process of trying to locate others of the same type to replace the one's that are missing.

If the ship is open to the public, like ours are, I strongly suggest taking extra precautions for safety.

These ships were built to be occupied by military personnel with training and are now public museums that will be crawling with people of all ages at the peak of the season.

The safer, the better so I am definitely opposed to attempting to repair the old transformers. I don't care if there are stories of submerged trannys being dried out and working for 20 years. Would you dry them out and sell them to someone, or would you rather not risk the liability? If you are (as you should) be hesitant to sell them due to liability, you should be just as concerned about using them for the same reason.

 

[Besoeker]

If enough fault current passed to blow 100 amp fuses on the primary side, then this may suggest that significant damage has been done and that replacement/rewinding may be the only option.

I'm inclined to agree.
At 20 kVA, replacement just might be a less costly option.

 

[BJ Conner]

I'm inclined to agree.
At 20 kVA, replacement just might be a less costly option.

True, but who want's a Seimens, or worse yet a chinese transformer on the old lady?
If whover made the transformer is still in business I would approach them to repair or replace the thing.
BB55 use to have Misubishis trying to sink it, it wouldn't be right to have one inside it.

 

[broadgage]

Would a modern transformer fit inside the case of the old one ?
Thereby preserving the original appearance.
Take the entire insides out of a modern transformer, reusing everything except the case. Might need de-rating but you should find that modern transformers are smaller and that a larger rating could be used if needed.
Alternatively keep the old one on view and de-energised whilst a modern one hidden somwhere is used instead.

 

[hurk27]

I had a transformer that was submerged in salt water once, never energized, but we were told that even drying it out would still leave a salt deposit, they said the only way was to flush it out with de-mineralized water a few times then dry it, we did and it worked fine for about a year:roll:

 

[zog]

True, but who want's a Seimens, or worse yet a chinese transformer on the old lady?
If whover made the transformer is still in business I would approach them to repair or replace the thing.
BB55 use to have Misubishis trying to sink it, it wouldn't be right to have one inside it.

Replacement at that size makes economic sense but I agree it would be a shame to put something other than original there. My company reconditions dry type transformers and specialize in this sort of project.

But NEMA recommends replcement
http://www.faecstate.org/Misc/NEMA-WaterDamageGuide.pdf

 

[bb55fixr]

Update

Update

We have been running a salamander kerosene heater in the room with them. They are all slowly coming up to normal. Yesterday's reading were something like: A phases to ground-305Mohms on 1000VDC, A Phase to phase-3.5 on 500 VDC, B phases to ground-1491 and 1520 on 1000VDC, B phase to phase 0.9 on 500VDC, and C phases to ground-276 on 1000VDC, C phase to phase-
5.0 on 500VDC. Thanks for all of the advice so far. I will run down and take some pictures. This bank is off the tour and inaccessable to the public. We only use them for lighting the area when we are up that way for work and inspections. Since switching to CFLs the load on them has dropped a lot. After the holidays we are planning on applying some power to them using the AC welder and eventually putting them under a light load to assist drying.

BTW, I think some of the discrepancy in the readings is from having the heater aimed mostly on the center (B) transformer.

If you are down this way and want to visit you can ask for me, if we aren't jumping too bad that day I'll try to show them to you.

Terry