Re: Transformer behavior

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Steve,
           I think what you are really after is a measure of REAL 
power in vs REAL power out, not VA which is Wattless. You will have 
to deal with some pretty awful primary current waveforms on the 
primary side of your MOTs.

Regards,
Malcolm

On 8 Jul 01, at 11:03, Tesla list wrote:

> Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<youngs-at-konnections-dot-net>
> 
> List,
> 
> I need some help understanding power transformer behavior.  I just fired up
> a DC power supply for a twin TC.  The supply has 2 MOTs running off 120 V
> mains via variac, each MOT with a half wave voltage doubler, for a total of
> about 11 KV filtered DC.
> 
> My puzzle is how to separate input magnetizing current vs the input current
> actually supplying power to the TC.  My first instinct was to measure the
> total VA with the TC running, then measure the VA with no load on the power
> supply.  The difference would be the power going to the TC.  But not so.
> 
> Here are some measurements - the numbers are AC volts to the MOTS, no load
> magnetizing (mag) current, total current running a TC with RSG at a break
> rate of about 240, and the difference between the two VAs:
> 
> in=  90 VAC, mag=  90 VA, others not measured
> in=100 VAC, mag=200 VA, total=550 VA, diff=350 VA
> in=110 VAC, mag=572 VA, total=814 VA, diff=242 VA
> in=115 VAC, mag=858 VA, total=986 VA, diff=116 VA
> 
> No PFC caps were used.  The MOT cores seem to start saturating around 100
> VAC with no load.
> 
> As the voltage increases, the VA to the TC will go up, not down.  But the
> differences above have the opposite trend.  So, obviously, my understanding
> of transformers is lacking.
> 
> It appears as the MOTs are loaded, they must go out of saturation and become
> more efficient.  So it appears the only way I will know the power going into
> the TC is to measure the (DC) watts being drawn out of the power supply.
> Can someone please shed some light on what goes on with a semi-saturated
> transformer as the load goes from zero to the rated transformer load?
> 
> Thanks,
> --Steve
> 
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