Re: Capacitor Help

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: m.j.watts@xxxxxxxxxxxx 

HI Gerry,

On 18 Dec 2005, at 12:43, Tesla list wrote:

> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Gary,
>
> I agree to not let our guard down with LTR.  I suspect that when the
> variac is slowly cranked up, transients are still being introduced
> although they are probably less than when the power is applied all at once.
>
> Gerry R

The combo is still resonant - it's just that its resonant frequency
doesn't exactly correspond with mains frequency. A simple SPICE
model should show what happens. There is an element of chaos
about the behaviour but you still get peaks and dips in the
response. At wide gap settings with the variac cranked up this
shows up as erratic firing.

Malcolm

> >Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
> >
> >I also suspect that using an LTR-sized cap is not the panacea that's
> >often suggested as relating to mitigating damage from too-wide gaps.  On
> >paper or in simulation it makes sense, but with real NST's, particularly
> >when cranked above nominal mains voltage, NST's may behave differently
> >than the models predict.
> >
> >Consider this.  A properly set static gap is set to fire at a voltage
> >just above the peak no-load secondary voltage.  Now we hook up
> >everything and slowly crank up the Variac.  If there was no mains
> >resonant rise, the gap wouldn't fire until the Variac hit nominal.  But
> >in practice, it starts firing at a far lower voltage.  Resonant rise,
> >no?
> >
> >I think using an LTR cap is a very good thing as it permits bigger bangs
> >and hence longer sparks.  But I don't think we should lower our guard
> >against setting our gaps too wide - it's not guaranteed to be safe.
> >
> >Regards, Gary Lau
> >MA, USA
> >
> > > Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
> > >
> > > Hi Terry,
> > >
> > > LTR caps wont prevent the high voltages that can damage the NST if
> > > the spark gap is opened up too much.  Yes, LTR keeps the steady state
> > > response reasonable but the transient response will beat with the
> > > steady state response and allow the voltage to get fairly high (not
> > > as bad as an uncontrolled resonant rise).  Ive done computer
> > > simulations that show voltages can get as high as 28KVpeak (with a
> > > 15KV NST) with the gap opened up too much.
> > >
> > > True if the main gap is set properly, a safety gap is probably not
> > > necessary but the protection is only differential mode.  A three
> > > terminal safety gap will also give common mode protection in case of
> > > a secondary to primary hit. The main advantage of a safety gap, I
> > > think, is you set it once and leave it alone.  You are now free to
> > > adjust the main gap as you like and dont need to worry about
> > > remembering the maximum setting to not exceed.
> > >
> > > One persons thought
> > > Gerry R
> > >
> > > >Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>
> > >
> > > >Just resist the temptation to increase the main gap size to get
> > > >larger arcs.  But LTR MMCs should fix that risk anyway...
> > >
> > >
> > >
> >
> >
>
>
>
>
>