Re: Question: Rotary gap designs

Subject:  Re: Question: Rotary gap designs
  Date:   Sat, 12 Apr 1997 07:19:06 -0500
  From:   Tesla List <tesla-at-stic-dot-net>
    To:   tesla-at-poodle.pupman-dot-com

> >
> >
> >Hi all,
> >Are rotary gaps which "snake" the current through several of the disks
> >gap's in series or through several in parallel preferred?
> >
> >I'm wondering if their is a break even point between series and parallel
> >gaps vs power levels and break rates.
> >
> >Anybody have a strong preference/experience?
> >
> >Thanks
> >
> >Kyle Hunter
> >(Usual disclaimer for using company email account)
> >
> >
> Kyle,
> Series gaps are always to be preferred over parallel gaps whether in a
> static system or a rotary.
> Dave Sharpe and I, but especially Dave, have designed a number of series
> rotary designs.  I prefer our original jointly designed and built series
> rotary quench design for magnifier work and he prefers his own custom
> designed bi-phase series rotary quencher.  This actually quench to well
> for
> use in a common two coil system if made to the highest standards.  I
> found
> this out on my Nemesis coil three years ago and Ed Wingate, who now uses
> a
> series quench rotary on his magnifier also discovered that it is too
> fast a
> quencher for his twin system.
> Most amateurs 10 years ago had terrible times with quenching, mainly
> through
> lousey design and staying stuck in the ruts grandpa used to build
> around.
> Today, many amateurs can usestatic gap systems, alone, up to 5,000 watts
> and
> quench fabulously.  This is partially due to well designed series static
> gap
> systems, but is more the result of a more modern "fresh wind" in coil
> building topology.
> Series those gaps and use lots of 'em.
> Richard Hull, TCBOR


A few comments concerning the biphase rotary.  It was
designed to allow 50% duty cycle on the fixed electrodes
by the arrangement of the disk and fixed strap bus bars around
the circle of the gap.  I have a 10 point (6 active) and 6 point
(4 active) biphase gap systems built for a 5kVA and 1kVA magnifier
respectively.  With a series rotary, electrode sizing becomes
tricky. Enough dwell time must
be allowed for the gap to commutate.  The primary advantage
of both series gap derivations is apparent approach and 
separation velocities are increased by the number of active 
pairs of electrodes. The biphase rotary gap at high powers
may have slightly less losses than a normal straight series
rotary due to lower parasistic inductances strapping adjacent
electrodes together.  

The simplest 6 point deriviative is shown below

         X      X
        /        \          O = Fixed electrodes
 ===O' X          X 'O====   X = Rotary electrode radially   
                                spaced 60 deg on gap wheel
         X------X           --- = strap bars between rotating
         O------O                 and fixed electrodes
                            O','O = Main HV input electrodes

As can be clearly seen the gap will fire on the upper 180deg
and when the rotary wheel rotates 60deg either direction will commutate
through the lower semi-circular path. The number of total electrodes
follow the
arithmetic progression of 2(2n+1); the active electrodes follow the
of 2(n+1).  One active electrode per approx. 2kV input should be

n    Active elctrodes   Total Electrodes        kV input Range
1       4                       6               8
2       6                       10              12
3       8                       14              16
4       10                      18              20
5       12                      22              24

With a very large number of electrodes, duty cycle on all electrodes
main HV electrodes approach 50% duty cycle.  I also run high pressure
blast perpendicular to wheel (air blows out of paper toward reader).

A derivative of this design with magnetic blow-out augmentation is being
given serious consideration for use on the large 20-30KVA machine Alex
Tajnsek is going to build.