Resin-Encapsulated Coils in Transformers

RF technicians use a device called a Time Domain Reflectometer to detect shorts in coaxial cable. I'm not sure if such a device would work in this case.

You might get a better and faster response if you posted this question in the Electrical Engineering and Communications & Electronics areas as well.

With care the encapsulation material can be removed to allow you to perform a visual analysis of the transformer coil. As a former electrical test laboratory technician I regularly did this. I never met a form of encapsulation I couldn't defeat.

As for your actual fault (ignoring the possibility of the customer overloading the transformer causing the winding insulation to heat up and fail at its weakest point), it is probably something as simple as damaged, improper curing or non uniform thickness of the winding varnish which is providing the insulation between the turns of the winding. Check your winding process and winding wire storage procedures to ensure that the winding wire insulation is not being damaged during handling and assembly. Also check the quality of your winding wire to ensure that it is not defective or has a temperature rating that is too low for the application.

Are you drawing a vacuum in your resin 'potting' process? That should eliminate air bubbles.

Hi,

Yes , our potting process is carried away by vaccum machine..

Hi,

depending on the core`s shape and the windings density its sometimes possible to detect failures by taking a roentgen picture - wi did so with rather simple ring cores.

Regards Uwe

Basically you should improve your winding techniques if you are getting lots of failures. This would probably be simpler than trying to find the fault in potted cores.

Are you testing them before encapsulation or after? Testing before eliminates wasted time & material. Testing after insures a Quality product is being shipped.

Resistance,insulation resistance tests should both be done before and after encapsulation until root cause is found. Wire could be scraping somewhere in the winding process or the insulation may be cracking due to tight radius turn or brittle / defective enamal.

Sounds more like a process problem rather than a field failure. Is your varnish compatable with the wire coating?

If you need any further help, let us know.

Good luck

Hi,

We do 100% inspection before & after potting .. Products are despatched at good condition..

Yeah, we also taking action to prevent the reccurence & the same is in line...

Despite, I'm little curious to know the instrument avail off the rack/ invented to scan the encapsulated parts...

Hari

Which ones are you having failures with c.t. or p.t.? This would make a difference on which type of machine your looking for to look at your windings. Is the current the problem or the voltage? I'm thinking because the windings are encapsulated you might have a problem with heat dissipation in the c.t's.

I've used an ultra sound machine to detect faults in bolts, the wave was generated and bounced back to the screen. The distance was displayed on the screen if there was a break or weak area. You could try this, but it would only tell you of the fault and not the cause. If all the test were done prior to shipment then rip and tear migh be the only option. Then examine under a microscope.

Are you using fish paper between the windings?

Hi Tippy,

we're using polyester tape as an insulating material b/w pri & sec..

Fish paper not used..

Hari