[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [TCML] Re: The truth about LTR, STR, and resonant modes
Hi Terry
Found them at:
http://hot-streamer.com/temp2/Old2001Files/2001-06/RESCHRG1.gif
http://hot-streamer.com/temp2/Old2001Files/2001-06/RESCHRG2.gif
On Friday 30 May 2008 10:52:26 pm piranha wrote:
> Let me know the "exact" old links, and I will dig them up :D But they
> are probably here:
>
> http://hot-streamer.com/temp2/
>
> Terry
>
> bartb wrote:
> > Hi Tony,
> >
> > Richie showed a "procedure" of sorts for resonant charging. BPS is a
> > part of it. I think you showed this since you adjusted the gap, the
> > bps changed, and "best running" input voltage had changed. I'm not
> > sure it's correct to correlate the observation to resonant mode
> > running, but the affect of BPS was certainly real. Here is Richie
> > Burnett's TCML email from 2001 on this subject. I find this email very
> > interesting and I'm not sure any of us are looking at PFC correctly
> > with our coils. I can't say that Richie is either, but I suspect
> > Richie was on to something here and his simulations showed him why.
> > The graph links I can't get to work. Their no longer at Hot-Streamer
> > (BTDT).
> >
> > Bart
> >
> >> > Original poster: "R.E.Burnett by way of Terry Fritz
> >>
> >> <twftesla-at-qwest-dot-net>"
> >> <R.E.Burnett-at-newcastle.ac.uk>
> >>
> >> > Hi guys,
> >> >
> >> > About a week ago, I said that I would go through my method for
> >> > designing the AC resonant charging circuit for a tesla coil.
> >> >
> >> > What I am going to explain is a way in which I propose that the
> >> > ballast and tank capacitor values for a particular system can be
> >> > determined at the design stage. i.e. You choose the rotary speed,
> >> > and how many kW of power you want, and use the following steps to
> >> > obtain the required ballast inductance and tank capacitance. As a
> >> > bonus this method also achieves good power factor.
> >> >
> >> > I should say that this is very much "simulation based" at this
> >> > stage, as I haven't built lots of different systems to prove every
> >> > combination. However, I have used Microsim extensively to verify
> >> > my work, and have got promising results. What little practical
> >> > work I have been able to do has also closely matched the predicted
> >> > performance.
> >> >
> >> > Ok, here goes......
> >> >
> >> > Let's say I want to design a Tesla Coil to process 10 kW of real
> >> > power, using a 12 kV power transformer, and a 371 BPS asynchronous
> >> > rotary gap. Power feed is from 250V -at- 50Hz, and at this stage I
> >> > have no idea what ballast inductance or tank capacitor value would
> >> > give good results.
> >> >
> >> > One possible approach would be to try many combinations of ballasts
> >> > and capacitors in simulations until the combination that results in
> >> > best performance is found. This is what I did and it was _VERY_ time
> >> > consuming ! I did this so hopefully you don't have to take this
> >> > hit and miss approach.
> >> >
> >> > STEP 1: Determine what the resonant frequency of the charging
> >> > circuit should be for your chosen rotary firing rate (BPS.)
> >> >
> >> > We know that the ballast inductor at the primary side of the power
> >> > transformer resonates with the tank capacitor at the secondary.
> >> > There have been many references to LTR caps. We are not concerned
> >> > with whether the cap is larger or smaller than a particular value.
> >> > We are only concerned with what the actual resonant frequency of the
> >> > charging circuit is. In this design approach there is nothing
> >> > special about resonance at 50 or 60 Hz.
> >> >
> >> > For a whole range of break rates, I tried simulating charging
> >> > circuits with different resonant frequencies. Particular attention
> >> > was paid to the charging waveforms and power factor. As I explained
> >> > before, it is the resonant frequency of the charging circuit which
> >> > determines all of the timing related stuff like how quickly the cap
> >> > charges between firings, and the power factor. So the resonant
> >> > frequency should be made right to start with.
> >> >
> >> > The graph here...
> >> >
> >> > http://hot-streamer-dot-com/temp/reschrg1.gif
> >> >
> >> > ...displays what I think the resonant frequency of the charging
> >> > circuit should be for different rotary break rates to get a power
> >> > factor of 0.85
> >> >
> >> > In our example the rotary break rate is 371BPS so the charging
> >> > circuit should be designed to resonate at 85.2 Hz.
> >> >
> >> > That ensures a PF of 0.85 at 371BPS, and ties down the product of
> >> > the ballast and the tank capacitor, but there are still many
> >> > combinations that would give the same resonant frequency. Indeed
> >> > all combinations which give the correct resonant frequency do give
> >> > the same charging waveforms and good power factor ! As long as
> >> > the product of L and C is right for the chosen BPS, the resonant
> >> > frequency is right and the charging circuit works correctly.
> >> >
> >> > Choosing various combinations of L and C only changes one thing.
> >> > The _POWER THROUGHPUT_.
> >> >
> >> > STEP 2: Determine what the ballast inductance should be.
> >> >
> >> > If changing the ballast and tank cap values together only alters the
> >> > power throughput, then we can adjust these values to get whatever
> >> > power level we want. However if we don't know where to start, how
> >> > can we pick a value for one of them without guessing and trying
> >> > something first ?
> >> >
> >> > Well, a good place to start is by ballasting the transformer to
> >> > whatever power throughput we desire. In our example, the desired
> >> > power throughput is 10kW, so we need to work out what ballast
> >> > inductance will limit the transformer to 10kVA when its secondary
> >> > winding is shorted.
> >> >
> >> > 10kW represents a current of 40 Amps at 250 Volts. Therefore the
> >> > ballast choke should present an impedance of 6.25 Ohms. At our
> >> > supply frequency of 50Hz, that requires 19.9 mH of inductance.
> >> >
> >> > This figure of 19.9mH for the ballast is a "first-approximation".
> >> > Although it draws 10kVA when the transformer is short-circuited,
> >> > it is unlikely that this will give exactly 10kW of real power
> >> > throughput at our chosen break rate. Life is just not that
> >> > easy ;-)
> >> >
> >> > STEP 3: Adjust the ballast inductance depending on chosen break rate.
> >> >
> >> > If we used the ballast value calculated above, the real power
> >> > throughput would be somewhat less than our desired 10kW. The actual
> >> > shortfall depends on the rotary break rate.
> >> >
> >> > The graph here...
> >> >
> >> > http://hot-streamer-dot-com/temp/reschrg2.gif
> >> >
> >> > ...shows what the real power output is as a fraction of the
> >> > "ballasted VA" for different rotary speeds. Notice that low speeds
> >> > give almost the full "ballasted VA" as real power, but higher speeds
> >> > give progressively less real power for the same ballast setting.
> >> >
> >> > For our chosen rotary speed of 371 BPS, it can be seen that the
> >> > running Tesla Coil would process only 64% of the 10kVA that it was
> >> > ballasted to draw with a short-circuit. Therefore we must multiply
> >> > the ballast inductance by 0.64 to correct for this shortfall and meet
> >> > the desired power throughput criteria.
> >> >
> >> > 0.64 x 19.9mH = 12.74 mH
> >> >
> >> > The "corrected" ballast inductance is 12.74mH, and this is the value
> >> > that we must use to get our full 10kW of power throughput when
> >>
> >> running.
> >>
> >> > STEP 4: Calculate the required tank capacitor value.
> >> >
> >> > Now that we know the ballast inductance, and the resonant frequency
> >> > of the charging circuit, we can finally calculate what the tank
> >> > capacitance should be.
> >> >
> >> > First we need to imagine that the ballast inductor is at the high-
> >> > voltage side of the power transformer, instead of at the low voltage
> >> > primary side. This enables us to deal with the ballast inductor and
> >> > tank capacitor like a series resonant circuit. The equation:
> >> >
> >> > F = 1 / [ 2 pi sqrt (L x C) ] can then be used as normal.
> >> >
> >> > In our example the power transformer steps 250 Volts up to 12000
> >>
> >> Volts,
> >>
> >> > so it has a turns ratio of 48. Impedances are transformed by the
> >> > square of the turns ratio, so our 12.74 mH ballast inductor becomes
> >> > 48 x 48 x 0.01274 = 29.35 H when referred to the secondary side.
> >> >
> >> > Re-arranging our resonant frequency equation and plugging-in the
> >>
> >> values
> >>
> >> > for F (85.2) and L (29.35) gives us a tank capacitance of 119 nF.
> >> >
> >> > And that is it.
> >> >
> >> > To summarise the ballast is 12.74 mH and the tank capacitor is 119nF.
> >> > This gives us a system that processes 10kW of real power at 0.85 PF
> >> > with our 12kV transformer and 371 BPS rotary spark gap. (Running a
> >> > Microsim simulation with these parameters gave me 10080 W of power,
> >> > 11999 VA, and therefore a PF is 0.84)
> >> >
> >> > There are two useful advantages of knowing that the approximate
> >> > power factor is 0.85:
> >> >
> >> > 1. We can estimate the VA or current draw from the 250 Volt supply.
> >> > In this case the real power is 10kW, so the VA = 10000 / 0.85
> >> > The VA = 11.76 kVA, or 47 Amps from our 250 Volt supply.
> >> >
> >> > 2. We can calculate the optimum PFC capacitance to improve PF further.
> >> > With a PF of 0.85, the VARs are roughly equal to _half_ the
> >> > watts. Therefore we need 5kVAr of PFC correction capacitance
> >> > across the supply to achieve the absolute maximum power
> >>
> >> factor.
> >>
> >> > That is a capacitive current of 20 Amps at 250 volts requiring
> >> > 255uF of capacitance at 50Hz. This will cancel any remaining
> >> > reactive current and maximise power factor.
> >> >
> >> > Increasing or decreasing the power:
> >> >
> >> > Remember that all the timing type behaviour is determined by the
> >> > resonant frequency. If you want to double the power throughput of
> >>
> >> your
> >>
> >> > design, all you need to do is double the tank capacitance and halve
> >> > the ballast inductance. (Assuming the power transformer can cope ;-)
> >> >
> >> > This will process twice the power due to the reduction in impedance.
> >> > However, the charging waveforms, peak voltages, and power factor
> >> > are not changed because the resonant frequency of the charging circuit
> >> > has not changed !
> >> >
> >> > There is nothing particularly special about the design method
> >>
> >> described
> >>
> >> > here. All I have done is run a large number of simulations to find
> >>
> >> out
> >>
> >> > what works best at various break rates. Then I have condensed this
> >>
> >> data
> >>
> >> > into two graphs showing:
> >> >
> >> > 1. What the resonant charging frequency should be for various BPS.
> >> > 2. How much the ballast needs to be adjusted to get the desired power.
> >> >
> >> > Now you can work backwards from Watts and BPS to get ballast
> >>
> >> inductance
> >>
> >> > and tank capacitance reasonably easily. Think of this method as being
> >> > like a lookup table.
> >> >
> >> > Congratulation if you have read this far, I appreciate that this
> >>
> >> stuff
> >>
> >> > is heavy going !!! This kind of approximations and calculations are
> >> > ideally suited to a computer program, so I intend to produce a simple
> >> > program to do all this stuff automatically. It will ask for your
> >> > intended power level in kW and your rotary speed in BPS. It will then
> >> > calculate the suggested ballast and capacitor values as explained
> >>
> >> above,
> >>
> >> > but much faster than using graphs and a calculator.
> >> >
> >> > I hope that the above information is error free, and has provided
> >>
> >> some
> >>
> >> > insight into the work that I have been doing for some time. If you
> >> > have any questions, criticisms or suggestions I will try to deal with
> >> > them as quickly as possible.
> >> >
> >> > Regardless of whether you understand the method or you just use the
> >> > computer program, I hope this work will lead to bigger sparks for
> >>
> >> all ;-)
> >>
> >> > Cheers,
> >> >
> >> > -Richie Burnett,
> >> > (Newcastle, UK)
> >
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
>
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla