Hi Bill, if the primaries were connected in parallel, I would agree with
you. But, the in discussion case, the transformer primaries will be
connected in series which forces the primary current to be the same in both
transformers.
If the primary current is equal and the turns ratio is slightly different,
the primary voltage will divide as dictated by the turns ratio, forcing the
secondary voltage to be equal. The common point in the series connection
is floating in respect to ground or the voltage source.
I can't see how a low source impedance would change any of this. AC power
source impedance better be very low if there is to be any line voltage
stability. Otherwise, there would be large voltage fluctuations as the load
changes when various equipment cycles on/off. If a 100 ampere load causes a
voltage drop of 5 volts, then the impedance would 5/100 or .05 ohms. That
seems pretty low.
73,
Gerald K5GW
In a message dated 10/27/2011 9:24:36 A.M. Central Daylight Time,
wlfuqu00@uky.edu writes:
That depends on the impedance of the power source. If it is very low
this balancing effect would be minimal and there would be
current flow between the secondaries.
I have a 5kW plasma generator which is identical to the 3kW versions
except the 3kW has one transformer and the 5kW has
two in parallel. Obviously the transformers are very well matched.
73
Bill wa4lav
At 04:55 AM 10/27/2011 -0400, you wrote:
>Hi Mike. back feeding from one secondary to the other may not be such a
bad
> thing. That would force the primary voltage division to the two
>transformers to be exactly what is needed for equal secondary voltages.
>
>The primary current will be the same since they are in series. Secondary
>current would be +/- small amount as dictated by the turns ratio.
>
>Does that make any sense?
>
>My take on this is to hardwire the two transformers (after phase
>confirmation) and standby for sparks
>
>Very interesting application!
>
>73,
>Gerald K5GW
>
>
>
>In a message dated 10/27/2011 3:37:53 A.M. Central Daylight Time,
>mike@tubby.org writes:
>
>Carel,
>
>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,
>then:
>
>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:
>
>http://en.wikipedia.org/wiki/Rectifier
>
>
>Regards
>
>
>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@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@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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> >>>
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> >
> >
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