Re: House wiring and transformer voltage regulation

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

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 > > > >  > >  > >
 >
 >
 >