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

[David Sharpe <sparktron01@xxxxxxxxx>]

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

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