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I did the Hi-Pot tests today on the #12 teflon insulated wire. The 12" long piece of wire was layed on top of a aluminum plate which was grounded to the Hi-Pot tester. The wire was connected to the 'hot' side of the Hi-Pot tester. I set the controls for A/C voltage at 1 kilohertz with a level of 4500 volts. I turned on the tester and right away it made the wire give off a buzz sound with ozone being generated. I let it run for 2 hours and then inspected the wire. No damage to the Teflon insulation was seen. I tried 5000v DC and there was no arcing possible.

I am going to do some more tests Thursday on the #12 Teflon insulated wire with the Vaseline filling in the small air gap between the wire and the metal plate ground as see what effect it has on the ozone generation.

Thank you for the information Ha-Jo.

Mike

WE0H

WD2XGI

----- Original Message -----

From: hajo.brandt.dj1zb

To: rsgb_lf_group@blacksheep.org

Sent: Wednesday, February 01, 2006 7:30 AM

Subject: Re: LF: XGJ

Concerning dielectric breakdown:

I remember there had been similar problems in the construction of capacitors in coaxial circuits for UHF television tubes when mica had been used for the insulator dielectric, between metallic surfaces which were not fully plane but included some air. The trick to solve the problem was to employ a thin layer of pure vaseline grease (may be some one even knows somthing better) on both sides of the mica surface which filled the gaps formerly filled with air.

May be this can also be used for high power/high voltage antenna transformers to avoid arcing between windings.

We generally know that another medium to avoid arcing in mains power transformers is oil.

HW?

73 Ha-Jo, DJ1ZB

MIKE we0h schrieb:

So it appears to be a dielectric breakdown in one of the insulations of one or both of the core windings. Has anyone done a dielectric test on the Decca Litz wire? I did some on #12 THHN wire a couple years ago and it arced at 5kv AC at 1kc as well as 5kv DC. No burning but it made some Ozone smell and the frying sound. I'll have to do some hi-pot tests Wednesday on the #12 Teflon insulated wire I have on my transformer.

This is good information to know. Hopefully others down the road can use this data to design their LF stations.

Mike

WE0H

WD2XGI

----- Original Message -----

From: Warren K2ORS/WD2XGJ

To: rsgb_lf_group@blacksheep.org

Cc:

Sent: Tuesday, January 31, 2006 8:25 PM

Subject: Re: LF: XGJ

Mike,

The 50 ohm side was made up of Litz wire from the Decca tank coil. The loop side was #4 stranded wire with pvc insulation.
After examining the transformer close up it appears that the transformer arced from primary to secondary. This seems to be correlated with the damp rainy weather yesterday, the transmitter was running full power for 6 and a half hours before the transformer arced over.

--
73 Warren K2ORS/WD2XGJ
FN42hi
http://www.w4dex.com/wd2xgj.htm

-------------- Original message ----------------------
From: "MIKE REID" <>
> What type of insulation & wire gauge did you have before?
>
> Mike
> WE0H
> WD2XGI
>
>   ----- Original Message -----
>   From: Warren K2ORS/WD2XGJ
>   To: rsgb_lf_group@blacksheep.org<>
>   Cc: LWCA LF Reflector<mailto:lowfer@lwca.org>
>   Sent: Tuesday, January 31, 2006 5:18 PM
>   Subject: Re: LF: XGJ
>
>
>
>   Hello the list,
>
>
>         I disassembled the toroidal transformer in the loop ATU and found the
> cores to be good. I will attempt to pick up some teflon insulated wire tomorrow
> and rebuild the transformer, if all goes well will be back on the air tomorrow
> evening.
>
>   --
>   73 Warren K2ORS/WD2XGJ
>   FN42hi
>   http://www.w4dex.com/wd2xgj.htm<http://www.w4dex.com/wd2xgj.htm>
>
>    -------------- Original message ----------------------
>   From: (Warren K2ORS/WD2XGJ)
>   > Hello the list,
>   >
>   >   Many thanks for all the reports last night from Hartmut, Jean-Pierre
> (F5YG),
>   > Juan, Gary, and Roelof (Hope I didn't miss anyone!)
>   >
>   >   As many of you have noted the signal dropped off at 03:00 UTC. At 04:00 I
>   > noticed XGJ was very weak on the W3EEE 'grabber'. I went downstairs to the
> radio
>   > shack to investigate. The antenna current (measured at 50 ohms) was less
> than
>   > 100 mA ! It should be approximately 5 Amps from the Decca PA. I checked the
>   > Decca on a dummy load and it was ok. I tried the smaller transmitter and
> noticed
>   > a very high SWR. I went out and looked at the ATU, flashlight in hand. The
>   > secondary of the toroidal step down transformer had arced and burned through
> the
>   > insulation. I believe that the very high humidity played a part in the
> breakdown
>   > of the insulation.   I will have a look at the transformer today and may be
> able
>   > to repair it if the toroidal core is not damaged. I am hopeful that the
> core is
>   > o.k. since impedance measurements showed no change and I was able to run the
> 250
>   > watt transmitter into the antenna with a low swr after a period of time
> (after
>   > the tuner cooled down).
>   > I will of course use better insulated wire for the high voltage!
>   >
>   >
>   >
>   > --
>   > 73 Warren K2ORS/WD2XGJ
>   > FN42hi
>   > http://www.w4dex.com/wd2xgj.htm<http://www.w4dex.com/wd2xgj.htm>