Shortbus for the proper place of tape on where to put it that will depend on the following:

1. if the test that im going to do will not show any significant effect on transformer then I might just put tape outer side of core for stator and inner side of core for rotor.

2. if the test will show significant effect on transformer then I might put the tape in between of core and winding. But in this case I have to be very careful as well because tape will give a gap in between the core and winding that might affect the maximum magnetic coupling of winding to the core.

Yes it is submerged in oil and yes you are correct that the enamel insulation is breaking down together with temperature and one more thing is in higher temperature the oil could emit water moisture that would go in between the spaces of core and winding and in between of each loop as well. With water moisture plus temperature then you could have a pressure in the enamel coating that in turn will or may wear that coating.

 

Newbies, the kapton is made for this job. But since it is in oil, the kapton tape may not hold. I was thinking of kapton sheet, and it is made to go between core and windings. I don't know where you are located in the world, see my signature line on my posts There is a place on Ebay that I have gotten kapton from, that I can give you the link if you want. Many places won't sell small amounts, but they do.

There should be no problem with magnetic coupling due to the kapton, like I said it is made for protecting windings in motors and transformers.

You may have to change the type of wire your using in this. There are high temperature enamel magnet wires and even ceramic insulation magnet wire out there.
https://www.google.com/search?q=hig...s=org.mozilla:en-US:official&client=firefox-a That might hold up better under your conditions.

I'll bet, from what you have said, that these transformers start out working fine, but degrade over time. Correct? You may have to have the replacement of the transformers be part of a 'preventive maintenance schedule'. Rebuilding them after a change out.

 

Heard about e-bay but never tried it. I am working in middle east. I will put your suggestion in my list. Thanks

 

Another thing that might work for your situation, but it would take some fabrication. Put the rotary transformer in to a sealed housing. The housing would then keep the oil away from the windings. If you go with this solution I'd make the housing from aluminum or non-magnetic stainless steel.

 

Well I don't think isolating the rotating transformer from oil is possible. As what I know the purpose of the oil is to provide lubrication to the whole thing and in some way offers like a coolant

 

JDT, thanks for the response. Yes as a standard the winding are enamel coated. I agree it is an insulator but why it behaves like the surge arrester that it conducts and gave some resistance when the break down voltage is reached? Yes maybe I can use tape in ferrite core, wrapping a very thin insulation tape would probably help.

For a neat clean look so, the tape will lay flat.

I take the electrical tape and pull off the amount I need to make it around the core.

Then like rolling a cigaret, I roll the tape up about 1/2 in diameter.

Then I take a razor blade and cut it into even 3rds. Now the small width of tape will lay very thin and flat as you wind it on

Cheers,
kv

Edit: This would be for small cores.

 

To all respondents in this subject. I am so glad to spread the result of my testing, I got a promising result. First, I got two ferrite cores (primary and secondary) where primary has infiinite insulation from the inductor coil to ferrite core and the secondary has some insulation resistance of ~200Mohms which I am not so concerned of. I submerged the two ferrite cores in oil and put them in oven and heat it up to 360'F (gradually) then cool down slowly and once it's cooled down then I measured again the insulation of two ferrite cores and surprisingly the secondary dramatically dropped the insulation to <10Mohms. Second, injected a signal (5Mhz 20V) to the ferrite core that is leaking and compared it to the that is not leaking. The signal to secondary for good ferrite core is perfect where in for the leaking ferrite core the signal in the secondary arrives late (2.5uS). By the way I did'nt put any load yet so with load it may get worse. I still have some couple of test to do, I will post all the pictures and result here once I finished for everyones reference. If you can share some ideas like additional test let me know and I am so eager to hear your suggestion.