Dry out 240D:120/208Y dry Xfmr after flood

[GarwoodV6]

I have a 30 KvA 3PH 240D in 120/208Y out dry type XFMR in storage that was about half submerged by flood water. I read another thread here about drying out 1PH XFMRs (battleship North Carolina) by using a variac or AC welder connected to the primary winding and shorting the secondary in order to warm the coils to bake out the water in the winding insulation layers by applying low voltage and monitoring/limiting current. I have only one 0-150V variac with 10A max rated output. Can I power up one coil at a time on this 3PH XFMR to accomplish this, provided I keep the variac voltage low enough to limit the variac output below the 10 amp rating on the variac? What about the other two primary and secondary coil sets while I do this - leave them open, or shorted?

 

[zbang]

First question- did you flush out the floodwater's crap? No point in drying a transformer with dirt in it. And depending on the transformer and any insurance, would replacement be a better course?

After that, you need to heat the whole thing, so if you can reconnect either set of windings in parallel, put the single-phase power on that set.

 

[Birken Vogt]

I wonder if you can find a DC source. You want to keep the voltage low and the current higher, so it will warm up. It should act like a dead short to DC so there will be no back EMF and no appreciable voltage to arc over before it has dried.

 

[Ken_S]

Scrap it,

From NEMA

Transformers Exposure of transformers to water can cause corrosion and insulation damage to the transformer core and winding. The ability of the transformer to perform its intended function in a safe manner can also be impaired by debris and chemicals which may be deposited inside the transformer during a flood. Water and contaminates also can damage transformer fluids. Items Requiring Complete Replacement: All dry-type transformers regardless of kVA ratings All dry type control circuit transformers Items Which May Possibly be Reconditioned by Trained Personnel in Consultation with Manufacturer: Liquid-filled transformers (analysis of the insulating medium is required for evaluation of this equipment) Cast-resin transformers

 

[Birken Vogt]

NEMA = national electrical MANUFACTURERS association

They would rather you buy a new one that they MANUFACTURE

However the idea of drying out the windings by applying moderate current at near zero voltage came from generator manufacturers who are not quite so greedy (yet)

 

[winnie]

I have no comment about cleaning out the crud nor potential insulation damage. Speaking only about the circuit:

My best guess: open the delta, energize all the primary coils in series, and short all of the secondaries to neutral. If possible flip the polarity of one of the primary coils.

Jonathan

 

[Ken_S]

NEMA = national electrical MANUFACTURERS association

They would rather you buy a new one that they MANUFACTURE

However the idea of drying out the windings by applying moderate current at near zero voltage came from generator manufacturers who are not quite so greedy (yet)

This transformer was not in service.

The manufacturer says to toss it.

The OP posted online to a forum about a water damaged transformer. This thread will be here for quite some time.

If you sell it, you would have to disclose what happened to it.

I'm my opinion, it's not worth the liability.


We've had motors cleaned and dried many times. That happens in a shop followed by testing. This is not the same.

 

[Birken Vogt]

I am in agreement that it is not something to be sold or represented as new. But it is worth a try if it is worth something to the owner, IMO.

 

[GarwoodV6]

I wonder if you can find a DC source. You want to keep the voltage low and the current higher, so it will warm up. It should act like a dead short to DC so there will be no back EMF and no appreciable voltage to arc over before it has dried.

DC will not induce current flow into any of the other coils. It has to be AC.

 

[GarwoodV6]

Isn't the insulation waterproof?

And the core dipped/vacuum impregnated to keep the laminations from buzzing?

 

[GarwoodV6]

The XFMR is my own, and provides 120V in my shop.

 

[GarwoodV6]

The coils appear normal, no sign of dirt or debris, at least on the coils visible with the front cover off. I haven't pulled the top to look down into the coils yet.

 

[Birken Vogt]

DC will not induce current flow into any of the other coils. It has to be AC.

Agreed. Hook DC onto the other coils too. You are trying to warm it up with ohmic heating without inducing any significant voltage anywhere. AC will make it come up to voltage.

 

[electrofelon]

I would put a fan on it for several days then just heat it up (energize) and see if it works. If you have the capability to measure the no load losses, see if it's around .5%

 

[rambojoe]

It needs to be stripped and checked, not dried- the guy is in texas after all...
Its dry!

 

[GarwoodV6]

It needs to be stripped and checked, not dried- the guy is in texas after all...
Its dry!

What do you mean stripped and checked?
Or Texas... its dry?

If you're referring to climate you do realize that our climate in the East half is pretty humid, not at all like AZ where you are?

 

[rambojoe]

Im saying its dry...by now.
Id pull the whole cover off and make sure flood didnt bring debris into the thing.
Fasteners (taps and such) may have been comprimised too. Just give it a good look.

 

[GarwoodV6]

I looked it over, and other than what I would consider normal operation dust accumulation on the coils and insulation layers, and a settling layer of dirt and dust along the bottom of the cabinet and on top of the fiberglass bar holding the xfmr connection tabs, things look good. The coils, and associated insulation wrap and sheets are coated with the typical vacuum-impregnated insulation varnish and look good, though the steel that clamps the core laminations above and below the coils has much of the varnish peeled away and some surface rust showing. I know it is possible that the laminations may buzz if any water permeated the layers and caused rust. Energizing the XFMR will tell that story, but I won't do that until I'm confident that the coils are dry and ready. They all look like they are... but I don't have a megger; only my Fluke 189 DVM

 

[GarwoodV6]

Im saying its dry...by now.
Id pull the whole cover off and make sure flood didnt bring debris into the thing.
Fasteners (taps and such) may have been comprimised too. Just give it a good look.

It's been 2 weeks since the flash flood and I don't have a reference water mark around the XFMR storage location. It was sitting on a pallet and water may not have gotten up much above the bottom of the coils.
I have yet to put any power through any of the coils. I suspect my little variac wouldn't do any good, but I have pulled the sides and top off and let the sun work on it the last couple of days.