Re: Recent power arc experiments

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

Original poster: "boris petkovic by way of Terry Fritz <twftesla-at-uswest-dot-net>" <petkovic7-at-yahoo-dot-com>



--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "Bert Hickman by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>
> 
> Boris,
> 
> A very interesting experiment! However, I suspect
> that the relatively
> small physical size of the individual resistors
> (1500 ohm at 5 watts)
> and the high applied transient voltage were likely
> the source of the
> measurement problem. 
> 
> Instead of going through the resistive element, the
> transient voltage
> across each resistor most likely rose to the point
> where the element was
> bypassed ("jumped" around) or was internally
> overvolted and broke down.
> The former is likely with an inductive wirewound,
> while the latter is
> probable with a carbon body or film resistor. Since
> the voltage standoff
> limit of any resistor is a function of its element
> length, unless these
> were specially made long-bodied HV resistors they
> most likely
> over-volted and broke down during the transient.
> This would force more
> power to be dissipated in the airborne spark to the
> resistor chain,
> accounting for the reduced Joule heating in the
> chain. 
> 
> I observed something similar during an experiment
> some time back where a
> 120 volt 25W tungsten lamp was inserted in the
> current path between the
> toroid and a breakout wire. When current flowed
> through the lamp to air
> streamers, the lamp would light at a certain average
> brilliance.
> However, when power arcs were drawn from the wire,
> the lamp would
> actually get dimmer! Turns out, that under the
> higher current
> transients, the voltage developed across the
> filament was sufficient to
> cause (hidden) spark breakdown in the base of the
> lamp, thereby
> bypassing current flow through the filament. Using a
> linear halogen bulb
> solved the problem. 
> 
> It would be interesting to duplicate the resistor
> experiment with a
> chain of longer HV resistors capable of withstanding
> the peak transient
> voltage. Another alternative might be a long, small
> diameter water
> resistor.
> 
> -- Bert --

Bert,

Thanks for your comments and suggestions.
These were definitely not HV resistors but cheap 
resistors for low voltage  network (yellow body with
coloured rings on it describing their ohmmage) and
used in various power electronic devices I guess.
To our surprise, 9 of them in string survived TC
arcing experiments without destruction as was checked
latter!
Except their possible suspicious behaviour during fast
transients ,I'm ready to blame extra high frequency
itself for lack of heating effect to resistors.
Boy,there could be 20 Mhz or more here..
Attached arc looked even more brighter when    
6" long wire (for accepting the arc) was connected to
the first resistor of the  string instead of 3" long
wire. 
The structure and colour of that arc surely indicate
it can not be treated as corona arc ( ~200 k ,1 pF per
foot).

Where to look for  small diameter water resistor (I
haven't seen such thing before)?

Regards,
Boris
  

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