Re: [TCML] 35 KVA Vacuum Tube Tesla Coil

[Frosty <frosty90@xxxxxxxxx>]

>From faradays law of induction, the flux depends on the integral of the
voltage across primary (we are forcing this to be a sine wave becuase we
connect it to the mains). The current that flows is what ever needs to flow
to create this flux through the reluctance of the core. So if the secondary
is open circuit (no current), only a very small current (the 'magnetising
current') flows in the primary, which looks like a very large value
inductor. When you connect a load, some current flows in the secondary and
generates its own magnetomotive force, which cancels some of that from the
primary. Then, since the flux is flixed by the voltage, the primary current
must increase to compensate and keep the same 'total' magnetomotive force to
keep the same flux through the core.

So as long as you keep the voltages and the number of turns and the
frequency the same, the flux in the core stays the same. If you increase the
load, the secondary current goes up, the primary current goes up, but the
two effects cancel, so the flux stays the same. If you increase the voltage
across the primary (or reduce the number of turns), then by faradays law you
increase the flux, and beyond a certain flux density, you cannot easily
increase the flux any more, so the reluctance of the core seems to increase,
so the magnetising current increases. This is saturation.

On Fri, Jul 8, 2011 at 4:33 AM, Phil Tuck <phil@xxxxxxxxxxx> wrote:

> Wow that was news to me, I worked on the principle that the increased
> current flow through the primary winding must cause more flux to be created
> in the core. So either that is not the case, which I am not sure why, or it
> does increase the flux, in which case if it is the latter would the
> secondary flux increase cancel it out then? Otherwise what is happening?
>
> Regards
> Phil Tuck
>
> www.hvtesla.com
>
>
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of Steve Ward
> Sent: 07 July 2011 18:21
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] 35 KVA Vacuum Tube Tesla Coil
>
> Phil,
>
> It is *magnetizing current* and NOT the *load current* that saturates a
> transformer.  The magnetizing current is purely a function of the applied
> voltage integrated over time, which essentially means that with 50/60 HZ
> power there's just a specific input voltage at which the core will
> experience magnetic saturation.  So drawing more power from your
> transformer
> will NOT increase the chance of saturation, in fact its most likely to
> saturate with no load as the line voltage will be highest then.
>
> Roger,
>
> Great to see some really high power VTTC work.  Some thoughts:
>
> 1) is it possible to increase the operating frequency of the system?  I
> think you mention the Fres of 280khz, but have you actually measured the
> oscillating frequency while making sparks?  I found that getting the Fop
> above about 320khz tends to produce sparks that have straighter segments to
> them which tends to make the spark length greater for the same input power.
> I think the amount of plasma output is the same, but with the lower
> frequency it tends to get all twisted up and becomes shorter.
>
> 2) What is the capacitance of your voltage doubler?  Could you furthermore
> measure the leakage inductance of the power transformer feed, plus whatever
> the ballast inductance is?  I have a strong suspicion that these "level
> shifters" are really more just resonating with the total power supply
> inductance at 60hz which gives you more through-put.  If you consider the
> total energy storage of the level shifter cap, its often far too small to
> supply even half the energy that the spark consumes in 1 cycle of AC.  I
> think my tube coils had something like 10J worth of caps there, yet the
> energy per spark was like 100J or something, in which case the capacitor
> would end up looking like extra series impedance (aka, ballast).  But this
> is not the case, because it *does* increase power throughput, so i think
> its
> really that this series cap works to cancel out the series L of the power
> circuit.
>
> 3) with regards to power measurement.  Can you simply get a line-type
> current transformer and put a 1ohm resistor on the output (for example),
> and
> use an oscilloscope to view the wave-shape and its relative phase with the
> line voltage?  I expect the phase to be pretty good because the VTTC really
> looks like a resistive load, but the shape may be kind of funky, and likely
> asymmetrical due to the half-wave nature of the power supply.
>
> Anyway, i also suspect the 35kVA figure is a bit high, but to see it
> consuming 15-20kW (real power) would not be beyond my belief given the
> spark
> output of this machine.  I cannot maintain that sort of spark length at
> 60pps on my QCW solid state machine, and ive seen the input power to that
> machine get up to 10kW pretty easily.  These types of sparks require a lot
> of power.
>
> Steve
>
> On Thu, Jul 7, 2011 at 10:26 AM, Phil Tuck <phil@xxxxxxxxxxx> wrote:
>
> > PF issues aside, I would imagine the transformer core to be totally
> > saturated and most likely the ballast as well, unless it possess a
> > very substantial core size. The trouble then is that the sine wave
> > loses it's shape and the meter, depending on the sort used, will give
> > differing false results.
> > Therefore, your coil is actually more impressive than what you though
> > for the power Roger!
> >
> > Regards
> > Phil Tuck
> >
> > www.hvtesla.com
> >
> >
> >
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
>
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla