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

[David Sharpe <sparktron01@xxxxxxxxx>]

Also below is additional information on HVDC megohmmeter, dielectric
absorption testing.  The polarization index method mentioned is
routinely performed on oil filled transformers from 25kVA up, along with
oil testing.  You might want to consider getting the oil tested for metallics,
dissolved water, PCB's (should be less then 25 ppm).

http://www.aemc.com/techinfo/techworkbooks/megohmmeters/tech_megohm.pdf

Disclaimer: We use AMEC equipment, but this is not an endorsement
of their product.

Regards

On Wed, Mar 23, 2011 at 7:52 AM, David Sharpe <sparktron01@xxxxxxxxx> wrote:
> 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!"
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>>
>>
>>
>> _______________________________________________
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>
>
>
> --
> Dave Sharpe, TCBOR/HEAS
> Chesterfield, VA USA
>
> Sharpe's Axiom of Murphy's Law
> "Physics trumps opinion!"
>



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

Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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