Re: [Amps] single phase into 3 phase transformer

["Doug Ronald" <doug@dougronald.com>]

If you short the center leg's windings, the flux will have a longer path,
thus more loss. There will be perfect balance because all three core's coils
have precisely the same number of turns. Also getting at the wires will be
easier if you separate the end coil and short that leg. Your other
connections won't have to go around the center leg.

I'm not with you on counter intuitive, but the physics does work just fine -
so there you go!

 

> The only other issue is filtering. More capacitance would be needed.

I assume you are comparing 3-phase with single phase. Consider a choke-input
filter. The soft-start is easier, and the regulation is much better than a
capacitance-input topology.

-W6DSR

 

From: Fuqua, William L. [mailto:wlfuqu00@uky.edu] 
Sent: Wednesday, April 21, 2021 14:41
To: Doug Ronald <doug@dougronald.com>; amps@contesting.com
Subject: Re: [Amps] single phase into 3 phase transformer

 

It would seem that if you short out the center coil there would be a better
balance between the remaining two in case you need to parallel the two
primaries. 

  As I said these are multi-kW transformers 10 to 25 kW with eye-bolts on
some. I don't need full capacity of the transformers. The cheap static
converters simply run motors mostly on single phase and a capacitor in
series on the third to provide some starting torque in the right direction.
These will not work on 3-phase transformers in DC power supplies. 

   I have seen the shorting of windings on one phase, which is counter
intuitive, but the physics works just fine.

The only other issue is filtering. More capacitance would be needed.

73

Bill wa4lav

  _____  

From: Amps <amps-bounces@contesting.com <mailto:amps-bounces@contesting.com>
> on behalf of Doug Ronald <doug@dougronald.com <mailto:doug@dougronald.com>
>
Sent: Wednesday, April 21, 2021 1:29 PM
To: amps@contesting.com <mailto:amps@contesting.com>  <amps@contesting.com
<mailto:amps@contesting.com> >
Subject: Re: [Amps] single phase into 3 phase transformer 

 

CAUTION: External Sender


Simply short-out all the windings on one leg, probably one of the outside
legs to keep the flux path shorter. Then the two legs left will get all the
flux and behave like a single-phase transformer. Phase the two windings
remaining remembering that the flux circulates in a loop around the
remaining legs.

I have done this with my power distribution system and have found very low
loss in the now single-phase transformers.
73, Doug, W6DSR

-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Fuqua, William
L.
Sent: Wednesday, April 21, 2021 00:47
To: amps@contesting.com <mailto:amps@contesting.com> 
Subject: [Amps] single phase into 3 phase transformer

What is the preferred method to wire a 3 phase transformer to operate off of
single phase?
I have heard of several possibilities and happen to have a mess of multi kW
three phase HV transformers.

73
Bill wa4lav
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