RE: DC Resonance Charging Advice Sought

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

Original poster: "Dave Kyle by way of Terry Fritz <teslalist-at-qwest-dot-net>" <dave-at-kyleusa-dot-com>

Thank you for your responses! Please see my comments in line

=========================================
Dave Kyle
Austin, TX USA
Email: dave-at-kyleusa-dot-com


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, August 11, 2003 11:14 AM
To: tesla-at-pupman-dot-com
Subject: Re: DC Resonance Charging Advice Sought

Original poster: "Bert Hickman by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<bert.hickman-at-aquila-dot-net>

[Dave] SNIP

 >1.) I have yet to resolve the system grounding. Is it advisable to ground
 >the center point of the main transformer for safety (like an NST)? Or would
 >it be better to simply ground the negative side of the DC power supply? Or
 >let it all float and just ground the secondary?

Grounding the center tap of the HV transformer's secondary will result in
the minimum stress to its insulation system. The next best would be to
ground the negative side of the supply. The secondary side should not be
allowed to float, since you want to insure a solid path to ground for any
streamer hits to the primary circuit.

[Dave] The secondary will absolutely be tied to earth ground, sorry if I was
unclear about that. You raise an interesting point regarding stresses on the
transformer insulation, I had not been aware of that. I am leading toward
grounding the negative side of the power supply as I think that may provide
the best protection for the diodes and inductor in the event of a primary
strike (am I wrong?). My guess is that the transformer's insulation is
adequate for its rated voltages since it did not have the secondary center
tap grounded by default as is done on an NST.

 >2.) I am assuming this transformer is not shunted (current limited) but
 >short of dismantling it how can I tell? DC resonance charging is self
 >current limiting so that will not be an issue but I would like pull current
 >slightly higher than the transformer's rating.

The HV transformer looks like a standard plate transformer and it has no
shunts.

[Dave] Excellent! Thank you for identifying the transformer. Given its size
I would expect it should easily handle 10% to 20% over rated load for the
brief periods I expect to run it.

 >3.) Assuming the transformer is not shunted would there be any benefit to
 >adding PFC caps?

Probably not - the load that the HV transformer will see will primarily be
capacitive, so PFC's on the primary will not appreciably reduce current.
There's no reason to capacitive ballasting, since (barring reactor
saturation) current limiting is accomplished by the charging reactor.

[Dave] Great, that makes good sense.

 >4.) I have noticed in some of the very few DC coils documented on the net
 >that a clamp diode and air inductor are sometimes added to the charging
 >circuit presumably to protect the supply and caps from over voltage and
 >transients. Can anyone comment on the need for this?

The additional protection circuits are primarily there to protect the
de-Qing rectifier and charging reactor from high amplitude voltage
reversals when the spark gap fires (due to Blumlein effect when longer
length transmission lines or coax are used to connect the HV supply to the
spark gap and tank circuit). If you minimize the distance between the
output of the power supply and the rotary spark gap you should be OK.

[Dave] Because of my layer cake architecture I expect the interconnections
to be very short.

This leads to the question, on which side of the inductor the de-Qing diode
should be placed? Based on Richie's information and Steve's design I put it
on the power supply side but I have seen other references with the de-Qing
diode on the tank side. Any thoughts?