Re: Megger test.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Metlicka Marc by way of Terry Fritz <twftesla-at-qwest-dot-net>" <mystuffs-at-orwell-dot-net>

Hi greg,


Tesla list wrote:
> 
> Original poster: "Mr Gregory Peters by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>
> 
> Hey guys,
> 
> As afore mentioned, I priced a reconditioned pole pig at $1045
> Australian. However, they will sell me an unconditioned unit for $500
> Australian (about $250 US). They say the only test they will do on the
> transformer is a megger test. What is a megger test?

As many others have said, The megger is a "megohm" meter that pushes
upwards of 1500v into the windings and measures the leakage through the
insulation.
Not exactly sure how they do it, or why they cost as much as they do
(big bucks)
While i have used my meggers to check transformers that have been
flooded or might be damaged, but this is usually on 550v- step-down
transformers and It isn't a high enough voltage for the hv side of the
pole transformer. Now i have seen some call there "high pot" testers
meggers, and actually they work the same in principle, a high pot tester
will test the primary windings at there normal operating voltages.
Maybe ask these guys if there megger test is at the intended operating
parameters?
Also, if a 14kv pig is tested at say 30kv "high pot", It will actually
damage the winding insulation. I remember one instance where a tech
meggered the lv side of a 13,800v-550v transformer with his hand held
megger at a setting of 1000v on the low side, this produced 25kv on the
hv side and must have punched a hole in the insulation because the
mildly suspect trans. turned into a very large arc welder at power up
(and sorry to say, someone was hurt very bad loosing one eye).
If your people are friendly, just ask them to power the lv side with
240v and leaving the hv side open will at least show if the windings
will handle it? if no smoke erupts from the case, i would be safe in
saying that you're all set.
GE would come and high pot our transformers at a very high price tag,
very thorough, and they were actually able to give suspected hours of
operation left inside that magic smoke. Don't ask me how?
Hope this helps,
Marc


 Is this a reliable
> indication of the transformers integrity? Would you guys suggest saving
> for the reconditioned unit or buying the "as is" unit? I figure I can
> buy two of the "as is" uints for the price of 1 reconditioned unit, and
> the chances of both being duds are minimal. What do you think?
> 
> Cheers,
> 
> Greg Peters
> Department of Earth Sciences,
> University of Queensland
> 
> Phone: 0402 841 677