Trigger xfmr "grounding"

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

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-compaq-dot-com>

Another detail of triggered spark gap hookup that is stalling me is, what
to connect the "low" side of the trigger transformer secondary to.  Most
folks using an automotive ignition xfmr connect the low side to RF ground.
This makes sense in that it is the most appropriate place to reference the
trigger electrode voltage to for a field distortion gap configuration.  My
problems with this are twofold.  First, the trigger spark current will have
to travel through the ~1-2Kohm resistor in the R-C NST protection network.
I'm not sure how significant this is to a 30kV pulse.  The other problem is
that the RF ground is typically riddled with HV spikes, relative to the
mains and 3rd wire ground.  It's unclear how long the ignition xfmr pri-sec
insulation will survive this, as I would imagine that in a car, the low end
is chassis-grounded, while the primary may have a couple hundred volts max
on it if there is a C-D ignition.  I'm actually using an EG&G trigger
transformer, with a!
 pri-sec holdoff voltage of 1500V max.

Assuming a trigatron configuration with an NST (neither side grounded), the
best approach appears to be to have a 1Meg HV bias resistor between the
adjacent and trigger electrodes, and a pair of HV doorknob caps from each
side of the xfmr secondary to the adjacent and trigger electrodes.  This
leaves both sides of the xfmr secondary at an AC float.  So, how to bias
the low side of the secondary to a safe voltage /wrt the primary without
coupling too much HF to the primary side?  

Gary Lau
MA, USA