Rotor drying 1

[petronila]

Daer All

Now we are doing maintenance in a big synchronous motor, the rotor (110 V-250 A)is cero MegOhms but is due to was with water contact, we have to dry it but our oven don´t have the correct dimensions and is too small.

We are handelling many variables and wethink the best could be the use of DC Welding machine to dryied by JOULE.

What do you think about this?

Thanks for the Inputs

Carlos

 

[waross]

What was the quality of the water that contaminated the rotor?
I had to dry a rotor that had been contaminated with brackish water. Before I started I rinsed the rotor with fresh rain water (the only fluid available) to clean it. The machine was only 350 KW. We dried it out with a battery charger over the course of a couple of days.
This was a generator so we were able to spin it and with the stator shorted we dried the stator at the same time. We ran about 50% of rated stator current.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[oldfieldguy]

We recently had problems with the rotor of an improperly stored NEW 22,000 HP synchronous motor. Due to the amazing skill levels of our construction 'management' the wet rotor wasn't discovered until the motor was installed inside a building that would have to be dismantled in order to remove it.

How amazing? Several hundred thousand dollars of motor was covered by a blue plastic tarp and left in outdoors. When the contractor arrived to pick the motor up to install it, there was standing water inside the motor. This was reported to management who in their vast an infinite wisdom, ignored it.

Drying efforts included opening the motor to allow moist air to escape and to facilitate heating by external means, the liberal use of temporary electric heaters (1 x 30kW and internal space heaters that should have been energized from Day One) to raise the the rotor temperature over a period of time, the use of a DC welding machine to provide internal heating, and careful monitoring and testing of the winding (yes, it was wet, too) and rotor insulation resistances over a period of days.

It's a long, sad story. But I'm not bitter.

old field guy

 

[rmw]

We can tell...

rmw

 

[dicer]

Curious. Why weren't these sealed with something like glyptal?

 

[jraef]

Did you check out the FAQ I wrote on this some time back:

faq237-1157


"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[MiketheEngineer]

Oldguy -

Did it fire up??

 

[oldfieldguy]

Mike--

yes, indeed, it did. The drying efforts were heroic, the discussions of how we got to that point and who dropped the ball were trident, and in the end the best two outcomes: the motor ran, and I was right.

And the same bunch of doofii did the same trick to another motor at another site, but since we now had this EXPERIENCE...


old field guy

 

[petronila]

Dear ll,

Thanks for the answers,

The rotor now have 1.5 GOhms, we use a small welder during three days, 12 Hours daily applying 100 D.C. Amps (20 D.C Volts).

Regards

Carlos

 

[waross]

You may want to recheck the resistance after the rotor cools down.
The generator that I dried out was damaged by the water. We got the resistance above a resistance check that was done a few years before.
BUT
I warned the operators that once the generator was taken off line it must be sent out for proper repairs before being restarted.
What do I know?
The generator carried the load until we got two other generators back from the repair shop. They had to be shipped by an old freighter.
One day, the load was getting close to the capacity of the operating generator. Rather than start up a 600 KW set for just a little more load, why not use the 350 KW machine? It was working fine when we stopped it. I was not on site.
That was the last day that that generator ever ran and it didn't run long.
Moral; A high resistance is good but it may not tell the whole story. The next time the machine gets cold for a few days, (now or in the future) it may be well to recheck the resistance before restarting.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[petronila]

Thanks for your recommendation and good experience.

Regards

Carlos