Re: how does voltage from a wall plug vary with time
From: Nick Rouse (nick_at_rouse.123isp.co.uk)
Date: 02/12/05
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Date: 11 Feb 2005 16:40:36 -0800
Uncle Al <UncleAl0@hate.spam.net> wrote in message news:<420A4E25.357F5B08@hate.spam.net>...
> aasiyah wrote:
> >
> > Hi
> > if you would sketch how the voltage from the wall plug varies with
> > thime, how would it look like, how can you find it out? I know it has
> > something to do with three phase since it is in AC signal. (a wall
> > plug in Europe with three-phase, 50 Hz and 230V)
>
> A one-phase outlet is a remarkably clean sine wave. A three-phase
> plug is three remarkably clean sine waves with 120 degree phase
> shift. 50 Hz voltage is incredibly stupid from generator to user.
> Your fluorescent lights flicker and your transformers are less
> efficient. A modestly higher multiple of 60 Hz would be better for
> all.
>
> Equipment connecting, running, and disconnecting from the line cause
> reactance and capacitance glitches resulting in voltage spikes and
> sags. That is one reason why you plug anything expensive into a very
> good surge protector. Lightning and crass human stupidity (inclding
> linesmen) are two other reasons.
Although 50Hz lighting may flicker in absolute terms more than 60Hz
the
difference is not nearly as much as is perceived by those who have
lived
most of their lives in 60Hz areas when visiting 50Hz areas.
Experiments have
shown that long exposure to one frequency of flicker causes a
distinct
notch in the visual frequency response. In visiting America from here
in Britain, I find the lighting somewhat more flickery that at home
but not as much as American friends visiting here who find it hard
to see how I put up with such lighting.
Transformers built for 50Hz are not less efficient than those built
for 60Hz.
but plug in a transformer built for 60Hz into a 50Hz supply and it
will heat
up more. If built to operate at the same maximum magnetic flux levels
(by having proportionately greater core cross section or
proportionally more primary
turns or a bit of both) a 50Hz transformer would be more efficient
than
a 60Hz one although bigger.
Even higher frequencies give much smaller devices but not necessarily
much cheaper as
steps have to be taken to keep the losses down. 400Hz aircraft
transformers tend to use very thin laminations of cobalt iron which is
many times more expensive than silicon steel used at 50 & 60 Hz
The cleanliness of the sinewaves is very dependant on the nature of
the
load in your vicinity. A largely linear load will leave the waveform
clean
but substantial non-linear loads such as discharge lighting,
rectifiers or
non-power factor corrected switched mode power supplies can distort
the
voltage waveform for other users substantially. 5% harmonic
distortion is quite
common close to sights where such loads make up a large fraction of
the
power used locally.
The original question asked about wall plugs (sockets) in Europe.
Anti-phase
live conductors are never found in domestic supplies (although
building
sites use portable transformers that transform 240 or 230V down to an
earthed
centre tapped 110V). As stated in an earlier post three phase supplies
are very rare here in domestic situations and in the few cases they
are used
they tend to be fixed wiring. I have not come across any three phase
sockets approved for use in Europe that you would want in your house.
Nick Rouse
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