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moos
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Join Date: Dec 2011
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DC High Voltage Test

12/15/2011 5:43 AM

Hi every body

I've some question which need to be answered

why DC high voltage testers always generate negative voltage rather than positive voltage?

thanks all
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Anonymous Poster #1
#1

Re: DC High Voltage Test

12/15/2011 8:27 AM

We assume earth as positive and current flows from positive to negative. Now what happens when positive and positive are connected?
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Anonymous Poster #2
#2
In reply to #1

Re: DC High Voltage Test

12/15/2011 12:27 PM

We assume earth as positive

And I always used to think that zero doesn't have sign. .

Does it mean that the positive polarity lighnings would rather fly off than striking the ground?
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jack of all trades
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#3

Re: DC High Voltage Test

12/15/2011 12:48 PM

Well mine always generate positive voltage.

Could you please elaborate on what type of DC High Voltage Testers you are talking about and the application (is this perhaps for high voltage DC pulse cable testing)?

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Anonymous Poster #2
#10
In reply to #3

Re: DC High Voltage Test

12/15/2011 9:42 PM

I too agree. there are DC pulsed HV tests too where a given number of alternate pulses of specific charactristics (Rate of Rise, KV,...) , positive and negative are given.

Thiat is of course not strictly plain HV test.
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TonyS
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#4

Re: DC High Voltage Test

12/15/2011 1:43 PM

I'm going back to schoolboy physics as I remember it. Electron flow is -ve to +ve so that may provide your answer. IE electrons will flow from what you're testing to earth.

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wareagle
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#5
In reply to #4

Re: DC High Voltage Test

12/15/2011 2:03 PM

Tony

That true in the real world but somebody in the universities changed that. I recall some military guys were really having a difficult time with that concept because they had been taught - to + flow. I was told that as long as you make that mistake thru the whole calculation, it came out the same answer.
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TonyS
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#8
In reply to #5

Re: DC High Voltage Test

12/15/2011 9:28 PM

I tried to explain it to an apprentice, that was hard work! I knew the school he had been to had a Van der Graff generator, I had been to the same one, it's where I was shown the effects of an "electron wind". Thanks to health and safety it was locked away along with the other stuff I'd got to use. As I said I was resorting to schoolboy physics (my school days), unfortunately the kids never get to see these things now. Seeing a 500,000V discharge sticks with you, reading about it doesn't.

The last I heard the school had destroyed the Van der Graff, the Whimshurst machine and the Tesla coils. What a waste, they were fun!

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wareagle
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#6

Re: DC High Voltage Test

12/15/2011 2:08 PM

Anonymous Poster #1 and Anonymous Poster #2. Why don't you two guys register so I can throw rocks at you like I do some of the others. Lyn, Tony and Jack would love it. I thought there was a requirement you have to register before you could post.
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Anonymous Poster #2
#9
In reply to #6

Re: DC High Voltage Test

12/15/2011 9:38 PM

I thought there was a requirement you have to register before you could post.

That is correct I am deliberately anonymous (but there is nothing that you can throw the rock on AP#2). Of course that is provided you don't take earth as ref frame, in that case of course earth is not zero (and to think of it is not same everywhere too but then for all practical purposes it is zero)

BTW - do you too mean like AP#1 that zero has sign? or do you mean that there are no positive polarity lightning strikes? (these are the two statements on which you may throw lightning stones.
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SolarEagle
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#7

Re: DC High Voltage Test

12/15/2011 3:22 PM

It's the only way you could get a reading...

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Anonymous Poster (4); jack of all trades (1); SolarEagle (1); TonyS (2); wareagle (2)

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