# Higher Voltage Pole Pig

```Malcolm (and others):

A while back, Malcolm described a system whereby he planned to put a
fixed gap across a rotary to prevent the gap voltage from becoming too
great under worst-case misfire conditions. I'm thinking of doing the same
thing but for a slightly different reason. I've got a 19.9/34500 10 KVA
pole pig that I plan to use for both Tesla Coiling and other high voltage
experiments. I also have a 60A 140 volt ganged variac and a 28A 240 volt
single. This gives me the option of running 0-140 V in on the X1:X3 leads
to get about 20,000 Volts, OR running off the 240/280 Volt variac to get
up to 34500/40250 volts for non-Tesla use. My home-made LDPE plate-type
caps have 128 mils dielectric made up of a total of 32 sheets of 0.004"
thick LDPE sheet material, immersed in Shell Diala-X transformer oil, and
are designed to run with off a 20,000 Volt RMS source.

awhile, I did a "thought" experiment. Suppose you had a well-quenched
static gap (for example an air blast or vacuum gap) with a wider gap
distance (say 0.60 inches) connected in parallel with a series rotary gap
having a minimum total gap distance of 0.50 inches). Suppose further that
you ran the rotary at a speed that gave you 600 - 800 potential
breaks/sec. If you "just missed" hitting the rotary breakdown voltage
at the current minimum electrode position and would have to wait for the
next break, the static gap would then fire, preventing potential
overvoltage stress on the tank cap. This approach would, in effect, clamp
the maximum cap voltage to the peak voltage breakdown of the protective
static gap (Vgapmax). Normally the rotary would govern the operational
breakrate except for the misfire cases, which should be efficiently
handled by the static gap.

Now suppose that the pole pig secondary voltage is significantly
increased (40 KV). The capacitor would charge to Vgap for a longer
portion of each half-cycle, and assuming the pig/ballast could deliver
enough charging current, the capacitor would re-charge at a quicker rate
since it would be heading to a much higher peak value before being
discharged at Vgap - we should get more "hits" per 60 Hz half-cycle, and
correspondingly, more effective power transferred to the secondary.
Slightly more stress would be placed on the primary cap since its duty
cycle would increase, but in all cases it would be clamped to Vgapmax. I
can't see a problem with this approach, but I haven't tried it out "for
real", and am somewhat reluctant to do a smoke test without first
bouncing the idea off the experts in the group.

Comments, flames, constructive criticism are appreciated... :^)

-- Bert --
```