Re: House wiring and transformer voltage regulation

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

Original poster: "Hydrogen18" <hydrogen18-at-bellsouth-dot-net> 

I'll do some tests soon.

---Eric
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, August 04, 2004 7:27 AM
Subject: Re: House wiring and transformer voltage regulation


 > Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz>
 >
 > On 3 Aug 2004, at 17:05, Tesla list wrote:
 >
 >  > Original poster: "Hydrogen18" <hydrogen18-at-bellsouth-dot-net>
 >  >
 >  > Although I have never done precise measurements per say let me say
 >  > this. I have a pc running in my room, with 3 monitors on it(current
 >  > unknown) along with 2-3 100 watt bulbs. If I plug in a hairdryer it
 >  > drops voltage so far my UPS kicks(I remember testing it with a variac
 >  > and remembering that it cut in at 110 volts).
 >
 > Sounds like an unacceptable voltage drop to me. I guess your nomial
 > mains supply is 120V? If so, that represents a 9% drop which
 > indicates to me that either your wiring is defficient or you have
 > contact problems at or near the switchboard or possibly an aged pole
 > fuse. Something will be heating in an unintended place.
 >
 >  > I know shunts are used in welders to limit current, and the constant
 >  > current charateristics they provide are desirable. In terms of voltage
 >  > regulation, how does a transformer limited with a series inductor
 >  > limiting current differ from one with internal shunts(poor coupling)?
 >
 > They are pretty much the same thing and the equivalent circuit of
 > perfect transformer and uncoupled inductor is the same for both. Note
 > that the poor coupling is actually a function of relative winding
 > placement. If the primary and secondary were wound over the same pole
 > leg, the shunting wouldn't do a great deal.
 >
 > Malcolm
 >
 >  > ---Eric
 >  > ----- Original Message -----
 >  > From: "Tesla list" <tesla-at-pupman-dot-com>
 >  > To: <tesla-at-pupman-dot-com>
 >  > Sent: Tuesday, August 03, 2004 8:04 AM
 >  > Subject: Re: Dr R's 16KV 300ma transformer
 >  >
 >  >
 >  >  > Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz>
 >  >  >
 >  >  > On 2 Aug 2004, at 18:11, Tesla list wrote:
 >  >  >
 >  >  >  > Original poster: "Hydrogen18" <hydrogen18-at-bellsouth-dot-net>
 >  >  >  >
 >  >  >  > The 1600 watts isnt going to heat, it is magnetizing the core. >
 >  >  > I never said it was going to heat, somebody else did. I assumed (!)
 >  >  > that you were actually meaning VA. > >  > I thought the voltage
 >  >  drop relative to current draw was intrinsic to a >  > transformer. My
 >  >  mains voltage drops when current draw increases. > > By how much?
 >  >  (rhetorical question). Mind you, if it drops > significantly (Like
 >  >  more than a couple of volts or so) it might be an > indication of
 >  >  underrated wiring or the hint of some fault being > present. No
 >  >  transformer is lossless but unless they are specifically > designed
 >  >  to have poor regulation, they are usually pretty good. > > Malcolm >
 >  >  > > >  > ---Eric >  > ----- Original Message ----- >  > From: "Tesla
 >  >  list" <tesla-at-pupman-dot-com> >  > To: <tesla-at-pupman-dot-com> >  > Sent:
 >  >  Monday, August 02, 2004 8:07 AM >  > Subject: Re: Dr R's 16KV 300ma
 >  >  transformer >  > >  > >  >  > 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 > > > >  > >  > >
 >  >
 >  >
 >  >
 >