Re: high voltage measurement w/ divider

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

I suppose it would depend on why the first resistor failed... If it flashed
over because of overstress, given that the resistors are all in series and
see the same stress, you're probably right. However, if a resistor fails
because of a component defect, or because of a localized problem (flashover
to structural member), AND, you've done a decent design on the string (i.e.
the margin on each component is at least 1/(N-1), where N is the number of
things in the string), then you should be ok, because each remaining
component only sees a stress of N/(N-1) (i.e. assuming the failed component
failed shorted).

Actually, this whole discussion of measuring HV stuff in general just brings
up the fact that you need to consider failure modes when designing HV gear
in general, and even more so when designing with high stored energy.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, February 04, 2003 9:07 PM
Subject: RE: high voltage measurement w/ divider


 > Original poster: "brianb by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<brianb-at-antelecom-dot-net>
 >
 > Jim,
 >
 > I beg to differ. If one resistor fails (i.e. flashes over) the additional
 > stress on the rest will start a chain reaction ending with a high energy
 > discharge (but this is getting off topic).
 >
 > My 2-cents,
 > Brian B.
 >
 > -----Original Message-----
 > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 > Sent: Tuesday, February 04, 2003 6:52 PM
 > To: tesla-at-pupman-dot-com
 > Subject: Re: high voltage measurement w/ divider
 >
 >
 > Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>"
 > <jimlux-at-earthlink-dot-net>
 >
 > No shrapnel involved.. Even if one resistor fails, the rest will limit the
 > current, until they fail so you don't get the big peak currents needed for
 > explosions.. Big snap, smoke, flames, but probably not explosions.
 >
 > That's not to say that one shouldn't be careful with large amounts of
stored
 > energy available.... There are plenty of other places for untoward rapid
 > energy release..
 >
 >
 > ----- Original Message -----
 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > To: <tesla-at-pupman-dot-com>
 > Sent: Tuesday, February 04, 2003 5:11 PM
 > Subject: RE: high voltage measurement w/ divider
 >
 >
 >   > Original poster: "brianb by way of Terry Fritz <teslalist-at-qwest-dot-net>"
 > <brianb-at-antelecom-dot-net>
 >   >
 >   > Guys,
 >   >
 >   > Be careful. A failure of one resistor here will most likely cascade
down
 > the
 >   > string turning all the resistors and associated wiring into an
exploding
 >   > wire experiment with shrapnel flying everywhere. Carefully think this
 >   > through and provide plenty of safety margin before proceeding...
 >   >
 >   > If you want to see what an unexpected failure scenario can do check
out
 >   >
 >
http://www.briananddebbie-dot-com/images/Backyard%20Science/Quarter%20Shrinker/A
 >   > ccident/accident.htm
 >   >
 >   > Regards,
 >   > Brian B.
 >   >
 >   >
 >   >
 >
 >