[AMPS] Two XFMR in parallel

[Tom Rauch]

Hi Noel,

> Well and good, but your ESR argument in this case overlooks an
> important point, as power is supplied from the transformer secondary
> the secondary voltage drops. 1. The open circuit voltage difference is
> 60V (1950V to 1890V) 2. The full load difference is 10V (1880V @ 0.6A
> and 1870V @ 0.4V)

That is not correct Noel. I was calculating the no-load dissipation. 
The full load dissipation can only be higher, it can never be lower 
than the no load dissipation.

Assuming good power lines, the voltage drop you are alluding to 
comes almost exclusively from what is defined as "ESR" of the 
transformer. The ESR is composed almost entirely of dissipative 
losses in the core and windings.

If you know the open circuit voltage difference, and you know the 
ESR, the result will tell you with nearly perfect accuracy the 
MINIMUM heat in the transformer under any condition when the 
transformers are connected to the power mains.

> So as the higher voltage transformer supplies current (due to the
> voltage differential) its loaded voltage will drop (due to its ESR)
> until it matches the unloaded voltage of the lower voltage
> transformer. The reason for including the current equalising resistors
> is to increase the ESR of that transformer. As the current increases
> the voltage drop across the equalising resistor/s increases and the
> system reaches equilibrium.

It only reaches equilibrium through voltage drop across the 
dissipative ESR. We know what the voltage drop is, assuming the 
power line "stays put".  
 
> Now if the system is supplying power to an external load, the overall
> dynamics improve as the fully loaded voltages of both transformers are
> so close.

Dissipation can only get worse, not better.

73, Tom W8JI
w8ji@contesting.com

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