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Re: PFC Question
- To: tesla@xxxxxxxxxx
- Subject: Re: PFC Question
- From: "Tesla list" <tesla@xxxxxxxxxx>
- Date: Sun, 06 Nov 2005 11:11:16 -0700
- Delivered-to: chip@pupman.com
- Delivered-to: tesla@pupman.com
- Old-return-path: <vardin@twfpowerelectronics.com>
- Resent-date: Sun, 6 Nov 2005 11:14:04 -0700 (MST)
- Resent-from: tesla@xxxxxxxxxx
- Resent-message-id: <pDL8yB.A.cCH.CfkbDB@poodle>
- Resent-sender: tesla-request@xxxxxxxxxx
Original poster: "Dmitry (father dest)" <dest@xxxxxxxxxxx>
"someone else can explain" - yeah, sure! but there is no any community
here, so you can wait forever :-\
ok - setting at the midway point:
o---------------|
|*
3
> 3 L1
/ 3
/ |
| |
~230v M --------
| | |
\ |* |
\ 3 |
> 3 L2 load
3 |
| |
o---------------|------|
M - mutual inductance
M=k*sqrt(L1*L2)
ASSuming k~1 (toroidal core, single layer winding):
M=sqrt(L1*L2)
L1 and L2 - each consists of a half of all variac turns, so
L1=L2=0.25L, L - full variac inductance.
now let`s decouple the magnetic couplings - as L1 and L2 are connected
in a phase (pay attention to the "*" signs at the upper circuit),
then the circuit would be:
o---------------|
|
3
3 L1
3
|
3
3 jwM
3
|
~230v --------
| |
3 |
3 jwM 3
3 3 -jwM
| 3
3 |
3 L2 |
3 load
| |
o---------------|------|
M=L1=L2=0.25L, so:
o---------------|
|
3
0.5L 3
3
|
|
~230v --------
| |
| 3
3 3 -jw0.25L
0.5L 3 3
3 |
| load
o---------------|------|
the internal resistance of the mains is very small - we can neglect it
- right? so mains is a dead short across variac input, then:
-jw0.25L
----------------uuuu---
| | |
3 3 |
jw0.5L 3 jw0.5L 3 load
3 3 |
| | |
-----------------------
you see ---> jw*(0.25-0.25)=0
ZERO inductance! :-P
if the voltage at the variac output is 3/4 from the voltage at its
input , then:
L1=0.0625L
L2=0.5625L
M=0.1875L
o---------------|
|
3
0.25L 3
3
|
|
~230v --------
| |
| 3
3 3 -jw0.1875L
0.75L 3 3
3 |
| load
o---------------|------|
-jw0.1875L
----------------uuuu---
| | |
3 3 |
jw0.25L 3 jw0.75L 3 load
3 3 |
| | |
-----------------------
you see ---> jw*(0.1875-0.1875)=0
again - ZERO inductance! :-P
is that hard to understand?
> Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
> Hi Dmitry,
> I hope you're correct, however, the performance curves from powerstat
> may suggest otherwise. I'm having a hard time understanding how
> there can't be any series inductance when, say, the setting as at the
> midway point. Maybe you or someone else can explain this.
> Gerry R.
>>Original poster: "Dmitry (father dest)" <dest@xxxxxxxxxxx>
>>
>>you wanna say that if there`s a number of "toroid turns in series with
>>the load", then these turns are "seen" by the load as some
>>inductance? it`s wrong too - variac isn`t an inductive divider, the
>>voltage on the load doesn`t depend from the current through it, so
>>load doesn`t "see" any series inductance.
>>
-----
Neon transformers are doomed in Tesla service! I should know, I've
killed more of 'em than many pople have ever even seen in a life time.
25-03-96 (c) Richard Hull, TCBOR