POWER SUPPLY FREQUENCY STABILITY
Harvey Twyman
I've observed that during the day it slows down and at night it speeds up.
These observations seem to cancel each other out almost exactly and have
found that there is no apparent drift over long periods of time.
The supply frequency is obviously dropping in the day due to "Peak Demand"
but at night the frequency must be increasing above the 50 Hz.
QUESTIONS:
Is this "Time Stability" observation coincidence or is it controlled by design?
If so what is its purpose? If not how could it be put to good use?
All domestic clocks and watches seem to drift minutes a month due to either
temperature variations or poor calibration. Surprisingly even computers
and TV Teletext clocks do as well.
Harvey Twyman
About Me: http://www.Twyman.org.uk/CV
Victor Roberts
wrote:
>I have an old Clock/Radio that's powered by the UK 230V 50Hz mains supply.
>
>I've observed that during the day it slows down and at night it speeds up.
>
>These observations seem to cancel each other out almost exactly and have
>found that there is no apparent drift over long periods of time.
>
>The supply frequency is obviously dropping in the day due to "Peak Demand"
>but at night the frequency must be increasing above the 50 Hz.
>
>QUESTIONS:
>
>Is this "Time Stability" observation coincidence or is it controlled by design?
Design, at least in the US and I would assume in the UK.
>If so what is its purpose? If not how could it be put to good use?
To make sure that electric clocks run on time. So, you already are
taking advantage of it.
>All domestic clocks and watches seem to drift minutes a month due to either
>temperature variations or poor calibration. Surprisingly even computers
>and TV Teletext clocks do as well.
I assume you mean clocks not tied to the mains frequency. You can now
purchase clocks and watches that use the standard time radio signals
generated by various government agencies, (NIST in the US) to maintain
their calibration.
--
Vic Roberts
http://www.RobertsResearchInc.com
Clive Mitchell
Twyman <harvey...@yahoo.com> writes
>I have an old Clock/Radio that's powered by the UK 230V 50Hz mains supply.
>
>I've observed that during the day it slows down and at night it speeds up.
>
>These observations seem to cancel each other out almost exactly and have
>found that there is no apparent drift over long periods of time.
>
>The supply frequency is obviously dropping in the day due to "Peak Demand"
>but at night the frequency must be increasing above the 50 Hz.
>
>QUESTIONS:
>
>Is this "Time Stability" observation coincidence or is it controlled by design?
>
boosted to compensate at night time. The electricity supply companies
have a master clock that has a radio link to the MSF time transmitter at
the national physics laboratory in Rugby. This is accurate to a second
in about a million years (apparently), and is used as the basis for
their timing adjustments.
>If so what is its purpose? If not how could it be put to good use?
>
Many mains operated timing devices either take their timing by
monitoring the mains frequency, or have synchronous motors that derive
their rotational speed directly from the mains. The electricity supply
company adjustments ensure that these are very accurate.
>All domestic clocks and watches seem to drift minutes a month due to either
>temperature variations or poor calibration. Surprisingly even computers
>and TV Teletext clocks do as well.
>
Non mains timing derived clocks tend to have a very loose tolerance on
their timing crystal that means they don't keep time terribly accurately
over long periods.
The vintage electric clocks that used to be popular before the advent of
quartz mechanisms kept excellent time, and the cheapo mains powered LED
clocks keep excellent time too.
--
Clive Mitchell
http://www.bigclive.com
Andrew Gabriel
Clive Mitchell <cl...@emanator.demon.co.uk> writes:
> In article <6d32c0e5.03041...@posting.google.com>, Harvey
> Twyman <harvey...@yahoo.com> writes
>>I have an old Clock/Radio that's powered by the UK 230V 50Hz mains supply.
>>
>>I've observed that during the day it slows down and at night it speeds up.
>>
>>These observations seem to cancel each other out almost exactly and have
>>found that there is no apparent drift over long periods of time.
>>
>>The supply frequency is obviously dropping in the day due to "Peak Demand"
>>but at night the frequency must be increasing above the 50 Hz.
>>
>>QUESTIONS:
>>
>>Is this "Time Stability" observation coincidence or is it controlled by design?
>>
> Just as you describe, the frequency drops with peak loading, and is
> boosted to compensate at night time. The electricity supply companies
It's more accurate to say frequency drops when demand gets close
to supply. This isn't necessarily at peak load - it tends to be
when you get sudden jumps in the load and the supply boost lags
a bit behind.
It's all controlled from a control room in Reading. They aim for
a drift of no more that +-0.1Hz (and I don't think they fail).
A question which is often asked is "why?" given that many other
synchonisation zones around the world only aim for 1Hz drift.
The answer is simply because they can -- it was a kind of
challenge. No one ever came up with a real reason to maintain
the short-term supply frequency so accurately.
One time they overshot was at the end of one of the England world
cup matches. The referee allowed one more minute's extra time
that the control room had calculated. Having dramatically boosted
the supply capacity to allow for 30 million people all switching
on a kettle and flushing the loo at the same time (lots of extra
load from sewage pumping stations too) the supply frequency started
climbing quickly. They were just about to kill some of the excess
supply when the match finally finished and the load grew to match
the supply.
Sometime in the 1970's (1976 maybe), there was a mistake in reading
the TV schedules and control failed to account for two major TV
programmes finishing within seconds of each other. There was not
supply provision for the sudden load increase, and this plunged
most of the South of England into darkness for some hours. Had the
Dinorwig emergency resovior in Wales existed at the time, it could
have easily handled the mistake, but it wasn't there at the time.
(It can run up from nothing to nearly 2GW in 12 seconds which is
the fastest runup in the world and the highest output for a stored
resoviour system in Europe.)
The biggest ever jump in demand in the UK was at the end of Lady
Diana's funeral. This was handled in part by Dinorwig. A lot of
careful planning went into the load calculations for that. The
load profile during Churchill's funeral was examined. Another
factor was that there were no commercial breaks during the whole
funeral broadcast of several hours, so there was an expectation
that pretty much the whole country would be going to the loo at
the same instant at the end of the broadcast, as well as putting
on the kettle, etc.
--
Andrew Gabriel
JB
"Andrew Gabriel" <and...@cucumber.demon.co.uk> wrote in message
news:b7irm1$ji0$1...@new-usenet.uk.sun.com...
<snipped- fascinating utility techie stuff>
Top marks again Andrew!
The 'behind the scenes' view of the power utilities is always of interest.
There's a guy on uk.rec.subterranea who *lives* for Hydro Power. You should
see the detail in his surveys on his website.
I must look at careers in this area....(almost as much of a 'technical
niche' as lighting!)
cheers,
JB
TKM
Andrew Gabriel <and...@cucumber.demon.co.uk> wrote in message
news:b7irm1$ji0$1...@new-usenet.uk.sun.com...
Great stuff, Andrew.
Surely with a record that good, someone is going to put up a web site with
the real time plot of load and frequency vs. time for the grid so everyone
can watch.
Terry McGowan