Re: [TCML] Selecting and testing pole transformers...

[David Sharpe <sparktron01@xxxxxxxxx>]

Stand corrected, should read higher then 100 Meg-ohms, HV to LV windings.
If transformer has 2 high voltage bushings, readings from HV bushings to case
or LV windings (X1, X0, X2), should read higher then 100 Meg-ohms.  With
a 1kV DC megger, readings in the Giga-ohms is common, particularly between
HV and LV windings.  10 Meg-ohms or less is suspect!

Regards

On Wed, Mar 23, 2011 at 6:21 AM, Yurtle Turtle <yurtle_t@xxxxxxxxx> wrote:
> "Measure between the HV and LV windings and no
> resistance should be seen"
>
> I think you meant no "continuity" should be seen.
>
>
>
> ----- Original Message ----
> From: David Sharpe <sparktron01@xxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Tue, March 22, 2011 9:54:05 PM
> Subject: Re: [TCML] Selecting and testing pole transformers...
>
> Nick
>
> We test transformers professionally at work.
> You should ohm the windings prior to applying
> power (H1 to H2, and X1 to X0, X2 to X0 and X1 to X2).
> The values for X1 and X2 to X0 should be the same.
> Measure between the HV and LV windings and no
> resistance should be seen (we use a 1kV
> megaohmmeter and measure the HV winding to
> case [at least 100Megohm] and LV winding to HV winding
> [even higher resistance] ).
>
> A simple turns ratio test can be performed by putting
> 120VAC on the HV terminals and measuring the low
> voltage output.  As a simple example, if the high voltage
> (H1, H2 terminals) are 13.2kV, and the secondary
> terminals (X1, X0, X2) are 240V (120V-X1 to X0,
> 120V-X2 to X0, 240V-X1 to X2); the ratio of the
> transformer is 110:1 (13.2kV to 120V) or 55:1
> (13.2kV to 240).  This would mean you should
> see 1.1V on the nominal 120VAC terminals (X1 to X0
> and X2 to X0), and about 2.2V across the nominal
> 240VAC terminals (X1 to X2).
>
> The only other test that you can perform is dielectric
> absorption ( tan[phi] ), which is a good measure of
> the soundness of the insulation system in the
> transformer (overheated or overvoltage stress
> tracking or water in oil).  DO NOT high potential
> (HI-POT) test a transformer, it can permanently
> damage the insulation system causing a delayed
> but messy failure!
>
> Be CAREFUL, testing a high power transformer is
> hazardous!  Be sure if you're testing the turns ratio
> as above, you apply 120VAC to the HIGH VOLTAGE
> (H1,H2) terminals ONLY!  It also goes without
> saying that pole pigs are ABSOLUTELY LETHAL!
>
> Be safe!  If you have questions, ASK!
>
> Regards
>
>
> On Tue, Mar 22, 2011 at 2:18 PM, Nick Andrews
> <nicothefabulous@xxxxxxxxxxx> wrote:
>>
>> Okay, I am supposed to be getting a pole pig form one of our subcontractors who
>>does electrical work.  He says he has some even 15 and 25kVA units.  I want a
>>5kVA (I think) or maybe 10kVA unit.
>>
>> If I can go to his yard and test them out before selecting one, what advice
>>would those on the list give?  Sure, a bigger tranny gives room to expand, but
>>the bigger it is, the heavier it is and the more room it takes up.  And you soon
>>reach the limit of your electrical service to supply more juice!  Thanks.
>>
>> Nick A
>>
>>
>>
>> _______________________________________________
>> Tesla mailing list
>> Tesla@xxxxxxxxxx
>> http://www.pupman.com/mailman/listinfo/tesla
>>
>
>
>
> --
> Dave Sharpe, TCBOR/HEAS
> Chesterfield, VA USA
>
> Sharpe's Axiom of Murphy's Law
> "Physics trumps opinion!"
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
>
>
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>



-- 
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA

Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla