Difference between AC and DC megger
Difference between AC and DC megger
(OP)
Hi,
We need to test a new medium voltage vacuum breaker.
Manual says to us an AC megger. We have a DC meggar.
Anyone know the reason for the difference of
AC vs DC meggering?
Thanks,
Will...
We need to test a new medium voltage vacuum breaker.
Manual says to us an AC megger. We have a DC meggar.
Anyone know the reason for the difference of
AC vs DC meggering?
Thanks,
Will...






RE: Difference between AC and DC megger
All meggers output only DC.
What the manual means that it is a ac power operated megger (could be ac motor operated or eletronic) as against the hand-cranked one.
* I would go green if only I were not yellow *
RE: Difference between AC and DC megger
RE: Difference between AC and DC megger
I would say if you dont own a Hipot you have not done this type of testing before and are not qualified to do this test, you may want to consider a qualified testing agency, this test will cost you less than the hipot rental. You also need to do contact resistance (Do you have a DLRO?) and contact erosion inspection. A power factor test should also be done if it is new to establish baseline data.
RE: Difference between AC and DC megger
11kv bottles tested at 20kvrms
33kv bottles tested at 58kv rms
both for 5-seconds
dc testing is no longer recomended but these values were used before the change:-
11kv bottles tested at 30kv
33kv bottles tested at 70kv
RE: Difference between AC and DC megger
C-H VCP-W is 27/40kV for up to 17.5 kV for example
RE: Difference between AC and DC megger
Where do the X-ray's come from?
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RE: Difference between AC and DC megger
RE: Difference between AC and DC megger
The X ray tube in early commercial X ray machines was basically a vacuum tube diode with the plate anode mounted at a 45 degree angle to direct the X rays. It was fed with about 100kV AC and acted as a rectifier as well as an X ray generator.
Bill
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"Why not the best?"
Jimmy Carter
RE: Difference between AC and DC megger
Thanks for your responses.
Yes manual does shed some light as well, say to use an AC highpot.
Also warns about Xrays - so the last few comments cleared up my next question.
Last question - "A power factor test should also be done if it is new to establish baseline data. " from Zogzog.
What do you mean by this? I was reviewing the NETA testing standard and there is no mention of this? Please provide me some enlightenment.
Thanks again,
Will..
RE: Difference between AC and DC megger
2007 ATS 7.6.3.2.8 and 7.6.3.2.9 Pf are both Pf tests.
RE: Difference between AC and DC megger
Yes I missed it - here is what I found.
*9. Perform power-factor or dissipation-factor tests on each pole with the breaker open and each phase with the breaker closed.
*10. Perform power-factor or dissipation-factor tests on each bushing. Use hot collar procedures if bushings are not equipped with a power factor tap.
I looked up what Power-factor testing was.
(learned something new last 2 days)
Thanks lots.
Will...