Megger testing devices under vacuum.
Megger testing devices under vacuum.
(OP)
Numerous HVAC & transformer technical manuals warn not to Megger equipment under vacuum. Why?
A vacuum is close to a perfect insulator. What is the reasoning for the caution?
Thanks,
A vacuum is close to a perfect insulator. What is the reasoning for the caution?
Thanks,






RE: Megger testing devices under vacuum.
A perfect vacuum is a perfect insulator. But there are also not-so-perfect vacuums. They ionize easily. Especially if you put one thousand volts there.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Megger testing devices under vacuum.
If you have a vacuum, then you have no oil. Oil is an insulator.
When you apply a vacuum, it tends to draw water vapor out of the insulation. In the process the water vaporizes. Little bubbles of vapor within the insulation are points of voltage stress intensification.
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RE: Megger testing devices under vacuum.
Most manufacturers testing procedures give a minimum distance to maintain from the equipment under test.
Don't think that this applies to AC pressure testing though.
RE: Megger testing devices under vacuum.
Bill
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"Why not the best?"
Jimmy Carter
RE: Megger testing devices under vacuum.
Bosko
RE: Megger testing devices under vacuum.
The vacuum interupters are to do exactly that, interupt normal and fault current. Sometimes on MV units the vacuum bottles may be surrounded with sf6.
RE: Megger testing devices under vacuum.
RE: Megger testing devices under vacuum.
Also, the OP was about meggering HVAC equipment and transformers. Two examples where the term "Vacuum" may mean a reduced pressure that is susceptible to flash-over rather than a perfect vacuum.
Bill
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"Why not the best?"
Jimmy Carter
RE: Megger testing devices under vacuum.
RE: Megger testing devices under vacuum.
I would then assume Vacuum Insulated Circuit Breakers emit X-Rays while in their open state with rated voltage applied to the line terminal, unless electron streaming is inhibited due to the high vacuum?
Bosko
RE: Megger testing devices under vacuum.
The question was answered while I posted my last reply.
Thanks to all for the help!
Bosko
RE: Megger testing devices under vacuum.