Re: Megger test.

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

Original poster: "Crow Leader by way of Terry Fritz <twftesla-at-qwest-dot-net>" <presence-at-churchofinformationwarfare-dot-org>


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, October 06, 2001 12:04 PM
Subject: Re: Megger test.


> 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

I doubt this testing destroyed the transformer. The hipot sets I've seen are
all DC and run at very low currents. I'm not sure how this would make 25kV
anywhere, or that 25kV will destroy what sounds to be a distribution
transfomer rated at 13.8kV. It sounds like the transformer was a dud to
start with.

> 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


KEN