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Magnetic Quenching of Spark Gaps


From: 	TimRaney-at-aol-dot-com[SMTP:TimRaney-at-aol-dot-com]
Sent: 	Monday, September 22, 1997 2:27 AM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Magnetic Quenching of Spark Gaps

For Greg Leyh and All:  

I probably missed the earliest posts on magnetic quenching.  I am not aware
of attempts to use magnetic quenching for rotory spark gaps.  I would think
the aerodynamic properties (laminar flow) of the rotor would clear the ions
and assist in quenching.  My summary only addressed static gaps.
 Additionally, the magnetic field does not have to be "moving" per se or even
pulsed to influence charged particles, i.e.; electrons, ions, etc.  A
magnetic field influences charged particles regardless of the relative
motions of the two.  Even if the magnetic field and the electrons or ions are
parallel, they will spiral along the field lines.  

As for "lingering" electrons or ions existing after the gap fires, you have
to consider atomic recombination.  This phenomena exists regardless of what
gap you are using.  In recombination, the electrons attach themselves to
positively charged ions almost immediately (recombination rates vary from
microseconds to a couple of milliseconds).  The resulting atoms are then
neutral again (though ionized atoms are always around...a product of
terrestrial background radiation and cosmic rays.  Additionally, electron and
ion velocities (accelerated by the gaps' potential) can scatter and move away
from the gap.  You would have to design an experiment to show "a relatively
stationary ion cloud" exists around the stator and rotor electrodes of the
rotary gap.  I think the factors discussed above make this condition almost
non-existant.  Hope this helps!

TIM RANEY, TCBOR   

________________________________________________________________________
 
 From: 	Greg Leyh[SMTP:lod-at-pacbell-dot-net]
 Sent: 	Sunday, September 21, 1997 5:58 AM
 To: 	Tesla List
 Subject: 	Re: Magnetic Quenching of Spark Gaps
 
 Tim Raney wrote:
 
 [snip]
 > Magnetic quenching was (and is) used to "blow out" DC arcs in heavy-duty
 > switches used to switch inductive loads.  Same principle with the spark
gap
 > in the Tesla coil tank circuit.  Tesla used this method in his work
(Tesla,
 > 1894) and details are available in the older electrical engineering texts.
 
 But isn't the desired mode of quenching _very_ different for circuit
breakers
 and rotary gaps?
 
 In a CB, the objective is to _immediately_ quench any arc as soon as it
forms,
 in order to reduce the pitting of the electrodes.
 A stationary magnetic field around the arc is suitable for this, since the
free
 ions and electrons are rapidly moving, and F = qvB will tend to scatter
them.
 
 But in a TC rotary, the goal is to provide an undisturbed, low impedance
path
 for the primary current _during the entire 1st beat envelope_, and then
somehow
 clear the lingering free electrons and ions afterward, before the 2nd beat 
 envelope can develop an EMF across the gap.
 Since the lingering free electrons and ions after the envelope have little
net 
 velocity, it would seem that a DC or permanent magnetic field could not
provide 
 significant clearing action, and would only serve to disturb the arc during
the 
 1st beat envelope, when high currents are present.
 
 Therefore, if magnetic quenching in a TC rotary is to be effective, the
magnetic
 field must be pulsed, either by permanent magnets that ride on the rotor, or
by
 a pulsed, off-axis electromagnet surrounding the gap area.
 
 
 > For magnetic quenching to be effective, the magnetic field must be
 > perpendicular to the spark gap axis.  
 
 This is true for clearing a high current arc.  However, in order to clear a 
 relatively stationary cloud of charged particles from the gap area, the axis
 of the pulsed solenoid should be parallel to, but offset from, the axis of 
 the gap electrodes.  This arrangement would send the offending particles on
 a trajectory 90 degrees from the gap axis.