Re: Dr R's 16KV 300ma transformer

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 1 Aug 2004, at 19:15, Tesla list wrote:

 > Original poster: "Hydrogen18" <hydrogen18-at-bellsouth-dot-net>
 >
 > I guess shunted transformers can be done right(although the only other
 > kind I can think of are welders, which dont really matter much as long
 > as they burn well). But with my 4 pack I have a HUGE magnetizing
 > current(1600 watts!). I guess part can attributed to bad power factor
 > and the fact that the cores are running at 70000+ lines of flux per sq
 > inch. But why dont all transformers have shunts? I know the winding
 > over winding method prevents the use of them, but I'm sure shunts
 > could save more than one small transformer which was accidentally
 > shorted/wired wrong/etc.

Time for a bit of basic transformer theory perhaps. The reason most
transformers don't have shunts is because it would degrade their
regulation. NSTs and other current limited transformers are designed
to have poor regulation so that they don't deliver an unlimited load
current with a short circuit parked across the output. You can
imagine the mayhem that would be caused by shunted distribution
transformers - as soon as someone turned on a heater, the lights
would dim. The winding-over-winding method ensures that the coupling
between the primary and secondary is as high as possible given
insulation requirements.

      Shunts *do not* prevent core saturation. Using enough pole area
so that the flux density is kept within the ratings of the core
material does. Any transformer which has an excessively high
magnetizing current flowing in its primary either doesn't have enough
pole area for the core material used or has too high a voltage
applied to it.

Malcolm