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Re: some questions

Hi Jan,

At 03:59 PM 02/02/2000 +0200, you wrote:
>
>Prepare yourself, maybe these are dumb questions, but I'll have to ask
>anyway ;) :
>
>1 - grounding a center-tapped NST: now where to connect that CT to? Mains
>GND is bad idea, and not to the secondary RF ground either. The problem is
>that if one side of my NST fails, there'll be a +2kVAC..-2kVAC between the
>NST casing and one HV connector, and the mains connector clips are so
>badly designed for this NST they have virtually no distance at all to the
>casing. Not nice. 
>So do you in general need a third ground for the NST center tap?

Grounding can be a messy issue, but everything "I" touch like the power
controller is grounded to the AC wiring.  The wires between the controller
and coil only carry AC and no ground.  Everything at the coil side is
grounded heavily to the RF ground.  This includes the NST, motor, safety
gaps, secondary ground...  Both grounds can float by about 50 volts and
then a ton to MOVs start to clamp everything down.  I have Corcom dual
stage line filters at the NST, motor, and back at the controller but that
is more for RF interference.  All the AC parts inputs are protected by MOVs
or gaps to absorb direct strikes and send them to the RF ground.  If the RF
ground is lost, the AC wiring and the AC ground will stay clamped to a few
hundred volts which is within their ability to handle.  To get really high
voltage on the controller, AC line would have to be lost which would
require the output is lost too.  

>
>2 - on RF filters on the HV side of a NST: shouldn't the huge inductance
>of the NST (4000 Henry or so?), be in itself enough to make a >700kHz
>signal see an effectively open circuit?  Because, jwL would be larger
>than 20 Gigaohm (taken that the tank cap is shorted out). 

The problem is that a high frequency spike will hit the secondary winding
and the voltage may arc the outer windings.  that inductance is so big a
spike will get eaten only in the first layer where the voltage drop may fry
it.  Inductive filters have all kinds of problems so RC filters are popular.

>
>3 - I've a round metal (Zn/Sn/Fe) plate on both ends of a wax & urethane
>varnish filled secondary, and the growing suspicion that the bottom plate
>draws lots of power the from the primary. In style of those quarter/coin
>shrinkers... Is this so? Better tear&saw off the bottom plate?

I hate to tear on saw off things, but the bottom plate is probably a mess
for the primary losses.  The top plate can stay.

Cheers,

	Terry

>
>
>Jan
>
>--
>*************************************************
> Jan Florian Wagner
> jwagner-at-cc.hut.fi, petwag-at-kolumbus.fi
> http://www.dsh.edu.hel.fi
>
>
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