Re: In-Line 3-Phase Variac

Hi Mark,

Your Variac looks a good find must be more than 10kVA but how to use it
fully on single phase is a problem.

Yes your right you can not just parallel the windings for the reason you
have given.

But you can just parallel two and leave the other open circuit.  If you have
an other single phase Variac you can check for saturation.  Turn the voltage
up slowly and monitor the current.  As has been said before you will notice
when saturation occurs as the current will increase faster. If it does not
saturate connect the input to the wipers at one end and to the other fixed
end, then move the wipers till you find the saturation point. Next back it
off a bit.  That's your best power out input connection if you can find a
way of making the connection independently of the wipers.

You can't short one leg with the other two powered it will be just like
shorting any transformer.

You can use it as a current limited transformer, connect the supply to one
leg and take the out put from one of the others.  The unused leg will be the
magnetic shunt.  I have used a three phase transformer this way but because
the shunt is so good you will not be able to get much power out relative the
power rating but that could still be large from the size of it.

Do you want to use it as a Variac or as a variable inductor.

-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: 17 August 1999 11:15
Subject: In-Line 3-Phase Variac

>Original Poster: Mark Finnis <mefinnis-at-medicine.adelaide.edu.au>
>Hi Folks,
>Help needed from the engineers/professionals (Bert, Malcolm etc.)......
>You may recall I found a nice 3-phase variac, complete with control motor
>etc and posted a picture of this to the list several weeks back.  See:
> http://www.adelaide-dot-net.au/~mefinnis/images/variac_cf.jpg
>Now I have since been thinking about this and I have some concern.  Most
>3-phase variacs are simply 3 ganged single phase units on a common shaft
>.... easy !
>This unit is 3 linear windings, one on each leg of a double-E core.  I had
>originally planned to use the three windings (15A each) in parallel for a
>45A variac - very conservatively looking at the size of the cores and wire
>gauge.  However ....
>1.  Trying to visualize the core magnetic fluxes, if I simply parallel the
>3 windings there will be no continuous path for the flux to follow.
> Am I thinking correctly here ??
> Or has my lack of knowledge brought me unstuck again !
> (alternatively would this simply act as a form of current limiting)
>2.  Thinking further, if I used just the 2 outside legs in parallel, then
>the flux could take the center leg - providing the core area is sufficient
>(which I suspect it would be).  Is this an adequate solution, assuming my
>concerns are correct in point 1 ?
>3.  Taking the mental process another step.  Could I construct a current
>limited variac by running the outside 2 legs in parallel, then short the
>center-leg to the wiper ? (which could then be independently variable)
>Only problem with the idea in (3) is the wipers are mounted on a common bar
>which is motor controlled.  Separating the center wiper would be messy, but
>not impossible.
>All help and ideas appreciated.
>Many thanks