Re: transformer question
Sorry, I assumed that you all would assume that I wasn't talking about
grounding the cases. (and most of us know what they say about assuming)
Also, with the primaries is series, the voltage output of each tranny
would be half of the original output, so there would be no added stress
on secondary or case insulation when connected to double the halved
output voltage. I am aware of all you had to say, Rienhard, sorry for
what misunderstandings my lack of clarity may have caused.
On Wed, 25 Aug 1999 11:46:28 -0600 Tesla List <tesla-at-pupman-dot-com> writes:
> Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
> Hi Grayson, James (The FCG), all,
> > Original Poster: Grayson B Dietrich <electrofire-at-juno-dot-com>
> > Otherwise, I think that one could also wire both the primaries and
> > secondaries series, for the same effect.
> No, you canīt do that AND it wouldnīt work the way you expect. Hereīs
> why: all NSTs (known to me) are center tapped. This center tap is
> designed to be earthed (see Fa. Tomīs very good explanation as to
> why this is done). If you now series two such transformers and earth
> the cases like you are supposed to, you will effectively be shorting
> out the two "inner windings". Visualize what you are doing: your 1st
> earth goes to the 1st NST center tap and the second earth goes to
> the 2nd NST center tap, so you have just shorted out one half of the
> 1st NST and one half of the second NST. While this wonīt harm the
> xformers (as they are current limited), you will only have 1/2 of
> you are expecting, which is already only 1/2 of what the NST is
> capable of.
> ;o( ???;o)
> 2x NSTs 120V to 9kV-at-30mA each
> Series the primaries: 60V per primary
> => Each secondary half (!) gives you 9kV/2/2 or 2.25kV
> As you are seriesing 4 windings and shorting out the two
> inner ones, this leaves you with 2 x 2.25kV or 4.5kV, which
> is exactly one half of what ONE NST can supply in normal
> service life.
> >That way, each transformer would be running at half voltage, but
> >would it still double the amperage? I dunno, so stick with
> >paralleling them.
> Any time you series two voltage sources, you will increase the
> total voltage across the outer terminals. The current remains
> the same. The electrons are still being "pushed" by only the
> current of one xformer. If the two voltage sources are of unequal
> (current capability) type, then the maximum current you can pull
> from the seriesed source (within reason) is the lowest capability
> of the two. In the case of seriesing (in general) you DONīT
> need the same voltage or the same current ratings.
> If you parallel two voltage sources, then the voltage remains the
> same and the current increases (simply current "a" + current "b").
> You can use different supply currents(!). They do not need to be
> equal. That being said, you MUST (esp. with non limited sources)
> have equal voltages. Otherwise the two sources will be fighting
> each other and you will either get a lower voltage or not current
> "a" + current "b" (it will be less).
> Maybe you were confusing current and VA, however. To increase
> the VA of a certain setup, it makes no difference if you series or
> parallel the xformers.
> Series Example:
> 2x 120V to 9kV (non center tapped units !!) at 30mA
> Primaries in parallel, secondaries in series:
> Each unit: 9kV-at-30mA = 270VA
> Series setup: 2x9(=18)kV*30mA = 540VA, which
> is composed of 2x the unit: 9kV-at-30mA = 270VA
> or 2 * 270VA = 540VA
> Parallel Example:
> Source: same as above
> Primaries AND secondaries in parallel:
> Each unit: 9kV-at-30mA = 270VA
> Setup: 9kV*30mA* 2 units = 540VA, which, too, is
> composed of 2x the unit: 9kV-at-30mA = 270VA or
> 2 * 270VA = 540VA
> The series example will ONLY work with non center tapped (and
> grounded) secondaries. This being said, here comes the next
> limitation to seriesing high voltage xformers: You can series (and
> ground the newly "created" center tap) only two HV xformers,
> due to insulation problems. Each HV xformer is built to withstand
> (plus some safety margin) itīs own voltage only. If you series two
> of these AND ground the center tap, then each xformer never sees
> more than itīs own voltage. For example: when you series two 9kV
> xformers that way, then you donīt get 18kV above GROUND, but
> rather -9kV/0V/+9kV. Of course, you DO get 18kV at the end terminals,
> but each is only itīs own (rated) 9kV above ground. If you further
> want to series more xformers, this gets very tricky, very quickly,
> because you now need to insulate the next set (pair) of xformers
> at 9kV above ground with an isolation xformer, which needs to be
> rated at 2x the single HV xformerīs VA rating. Believe me, this
> ISN`T really worthwhile. This is also one of the reasons, why MOTs
> are not a too hot choice as a coiling PSU. What I mean is using
> more than 2 plus voltage doubling (and current "halfing"). For
> example, if you want to series 6 MOTs, you would need 12 MOTS
> total, using 6 of the 12 as the actual PSU and the other six to
> build the necessary isolation xformers. Of course, there are "tricky"
> guys out there (look at Jim Luxīs website), that have found a
> method to get around the isolation xformer problem, but these too,
> have their limitations AND more important, their expenses.
> Phew, pretty wordy, ha? Still, I hope it helped clear up some of
> the mystery, tho.
> Coiler greets from Germany,
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