[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

*To*: tesla@xxxxxxxxxx*Subject*: Re: Ratio of Med C or equivalent C to intrinsic C was Re: LC III*From*: "Tesla list" <tesla@xxxxxxxxxx>*Date*: Fri, 08 Apr 2005 17:14:46 -0600*Delivered-to*: chip@pupman.com*Delivered-to*: tesla@pupman.com*Old-return-path*: <teslalist@twfpowerelectronics.com>*Resent-date*: Fri, 8 Apr 2005 17:26:35 -0600 (MDT)*Resent-from*: tesla@xxxxxxxxxx*Resent-message-id*: <YfU01B.A.DMC.2GxVCB@poodle>*Resent-sender*: tesla-request@xxxxxxxxxx

Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>

Correction: I think in a previous post I suggested that the difference between Medhurst C and the value of C that gives the correct Fr for a no top load was about 40%. From numerical simulation some time ago I had remembered 18% and incorrectly assumed that was in frequency hence the "approximately 40%" figure I gave for C. Apparently from my post below the variation was in C not fr ie approximately 9% in fr which is a figure compatible with the observed errors between Medhurst fr and measurements.

Robert (R. A.) Jones A1 Accounting, Inc., Fl 407 649 6400 ----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx> To: <tesla@xxxxxxxxxx> Sent: Friday, April 08, 2005 11:00 AM Subject: Ratio of Med C or equivalent C to intrinsic C was Re: LC III

> Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx> > > > Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx> > > > > > > For the coils that I have measured, or calculated, the > > Medhurst capacitance is close to one half of the capacitance > > of a hollow cylinder to "infinity". > > And there is a good reason for this, because if the distributed > > capacitance of the whole coil is split in two, one at each end > > of the coil, Each of them is at the position of the Medhurst > > capacitance when the other end is grounded. Of course, this > > assumes that the grounding at one end doesn't affect much the > > distributed capacitance at the free end of the coil, what > > appears to be true. > > > > Examples (calculated): > > A coil with 1 m of height and 20 cm of diameter: > > Medhurst capacitance: 15.28 pF > > Distributed capacitance of a cylinder with this shape: 27.57 pF > > A coil with 1 m of height and 40 cm of diameter: > > Medhurst capacitance: 21.29 pF > > Distributed capacitance of a cylinder with this shape: 38.07 pF > > For a secondary with uniformly distributed L and C with no top load, > the lumped equation gives fr = 1/(2*pie*(Ld*Cl)^1/2)) > and the transmission line equation gives fr = 1/(4*(Ld*Cd)^1/2) (this > assumes a long coil compared to its diameter and that the wave length is > long compared to the mutually inductance function) > Where Ld is the inductance, Cd is the intrinsic capacitance and Cl is the > equivalent lumped C that produces the correct resonate frequency in the > lumped equation with Ld with no top load. > Hence Cd/C/ = (Pie^2)/4 ie 2.467. > > When the secondary is resonated with a large C the secondary voltage > linearly increases along its length. If the intrinsic C is assumed to be > uniform then 1/2 the current would flow in the intrinsic C. ie uniformly > distributed capacitance when referred to the end is halved. Hence Medhurst C > is half the intrinsic C ie Cd/Cm = 2, (only valid when resonating with a > large top load) > Actually the intrinsic C is distributed more toward the ends of the coil > with the greatest at the grounded end (its closer to the ground connection). > The C at the top end has a greater effect but is small value than the bottom > C. The bottom C is larger but has less of an effect. So the effect of the > uneven distribution biased towards the bottom end tends to cancel so I would > still expect the ration to be near 2. (with large top load). > > Note Medhurst test conditions differ from a typical secondary that operates > over a much closer ground plain and with a much smaller top load. > > Robert (R. A.) Jones > A1 Accounting, Inc., Fl > 407 649 6400 > >

- Prev by Date:
**Re: bummed** - Next by Date:
**Re: Name My TC** - Previous by thread:
**Re: V Bipolar was Re: An internal primary** - Next by thread:
**Build your own HV transformer** - Index(es):