[Amps] running two 3 phase transformer serie/parallel

Mike Tubby mike at tubby.org
Thu Oct 27 01:37:49 PDT 2011


I think what you were originally suggesting might work, as long as you 
have access to both sides of each primary winding.

If you call the phases Red (R), Yellow (Y) and Blue (B) as we used to in 
the UK, the transformers #1 and #2 and the ends of the windings A and B, 

     Red = R1A [primary] R1B --- R2A [primary] R2B
     Yellow = Y1A [primary] Y1B --- Y2A [primary] Y2B
     Blue = B1A [primary] B1B --- B2A [primary] B2B

each primary is in series and will see half-voltage.  You still need to 
know if you are to power it in 'star' or 'delta'.

On the output side the easiest (safest) thing to do would probably be 6 
x diodes, each one a half-wave rectifier and parallel the DC side going 
in to the smoothing - this way if one of the transformers provides 5-10V 
more off load than the other it won't back need another secondary winding.

Alternatively you could use two three-phase rectifiers and parallel the 
DC sides going in to your smoothing.

Rectifier arrangements are here:



Mike G8TIC

On 26/10/2011 10:40, pc5m, Carel wrote:
> Hi Gerald,
> We have here 400V 3 phase power (voltage between the
> phase's) and as a result 230V between a phase and ground. So the lowest
> voltage I have "available" is 230Vac...
> gl, Carel.
> On Tue, 25 Oct
> 2011 18:02:30 -0400 (EDT), TexasRF at aol.com wrote:
>> Carel, what is
> your primary voltage there? Do you have three phase primary power?
> 73,
>> Gerald K5GW
>> In a message dated 10/25/2011 1:11:15 P.M.
> Central Daylight Time, pc5m at xs4all.nl writes:
>>> Hi,
>>> I have
> two identical 3 phase high voltage transformer (each around 4KVA /
>>> 50
> kg/ 100 pounds). Issue is they are designed for US 3 phase voltages.
> (so
>>> 120 / 204V) so can't use them in Europe as is. What I would like
> to do is to
>>> put the 2 units at the primary side in serie and at the
> secondary side in
>>> parallel. Primary and secondary in wye config.
>>> Q: Would there be any benefit of connecting the secondary windings
> of the
>>> two transformers first parallel and than rectify (with only
> one rectifier
>>> bridge) or the other way around ? For me it is much
> easier to first rectify
>>> both transformers and than put the rectified
> voltage parallel (only one
>>> highvoltage interconnect between both the
> big/heavy transformer boxes.).
>>> I have seen some constellations
> with two 3 phase transformer to gain some
>>> benefit in creating
> additional phases in order to reduce the ripple voltage
>>> even more.
> Don't know if I could utilize such a thing as well ? However, if
>>> I
> recall they were placed in parallel at the input.
>>> Thanks for any
> idea's . Gl, Carel
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