[Prev][Next][Index][Thread]
Re: Pri-Sec Phasing
---------- Forwarded message ----------
Date: Tue, 7 Oct 1997 08:25:08 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: tesla-at-pupman-dot-com
Subject: Re: Pri-Sec Phasing
Greg, all,
I had a hard think about this last night and have an
appendage to my answer of yesterday (which was correct as far as it
went).....
> From: Greg Leyh <lod-at-pacbell-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Pri-Sec Phasing
>
> Malcolm, Bert, All,
>
> When the pri and sec are physically close to each other, the relative
> polarities of the pri and sec should be aligned, in order to minimize
> the voltage difference between them.
> Given all of the possible 'minus-sign' errors, and the fact that the
> two coils are 90 deg out of phase, should the coils have the same or
> opposite 'handedness' when wound?
> I am no longer completely sure of the correct answer, and would much
> appreciate a confirmation. If possible, a concise explanation of how
> the answer was obtained would be far preferable to anecdotal evidence.
Here it is. In a lumped situation where the coupling is tight and
winding senses are the same, voltage senses are also the same.
Induced current senses are also the same (because flux linkages are
pretty much identical) but are opposite in sense to the current being
driven into the primary from the power source. The equation describing
induced EMF is:
E = -L.di/dt (everybody ignores the minus sign, right? :)
This unfortunately delivers a blow to anyone who attempts to use
this equation to describe primary flux interaction with the
resonator in the 2-coil system. Without exception, all analyses I
have seen use the total secondary inductance for the variable "L" in
this equation to describe the voltage induced in the secondary. There
are two reasons why you cannot do this with k *significantly* below 1
*and* where the primary is located *at one end*.
First is the lack of flux linkage between the primary and
secondary *as a whole*. Proof: There is a 90 degree phase shift in
voltage from bottom to top of the resonator. That cannot exist if
flux linkages are identical at top and bottom. QED
Secondly, the top of the resonator is virtually uncoupled to the
primary. Proof: the toroidal terminal (shorted turn) has no
measureable effect on the primary. By the same argument, the primary
has no great effect on the top of the secondary. QED
*HOWEVER*, by virtue of close coupling between the *bottom* of the
resonator and primary, the voltages here *are* in phase so observing
winding sense is a very good idea.
Malcolm