Electrical Engineering - Accuracy of UK power grid time control?

Author

Accuracy of UK power grid time control?

Christopher Tidy

2006-04-14, 12:21 pm

Hi all,

I'm thinking of building an electronic clock control circuit which uses
the 50 Hz mains frequency for time keeping. The reason for this is that
the clock dial is rather large, so probably wouldn't run for long on
battery power, and I don't fancy spending £40 buying a programmable
quartz oscillator chip.

Despite doing some research online and in electrical engineering books,
I can't find a figure for the accuracy of the time keeping of the UK
power grid. Perhaps this is because there aren't official bounds set for
the time error - one of my electrical engineering books says it is a
legal requirement that the frequency be kept "as close as possible to 50
Hz" - but even if this is the case it should be possible to determine a
typical error figure.

From my point of view I'd regard an acceptable error as 5 minutes every
6 months. Does anyone know the typical time error seen on the UK grid,
or where I might find this information? Any suggestions would be much
appreciated.

Best wishes,

Chris Tidy

Mike Berger

2006-04-14, 12:21 pm

In the U.S. the power grid is very accurate over long periods of
time. But what are the odds of running six months without a single
power interruption?

Christopher Tidy wrote:
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending £40 buying a programmable
> quartz oscillator chip.
....

> From my point of view I'd regard an acceptable error as 5 minutes every
> 6 months. Does anyone know the typical time error seen on the UK grid,
> or where I might find this information? Any suggestions would be much
> appreciated.

Ralph Mowery

2006-04-14, 12:21 pm

"Christopher Tidy" <cdt22NOSPAM@cantabgold.net> wrote in message
news:443FBF5B.4090101@cantabgold.net...
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending £40 buying a programmable
> quartz oscillator chip.
>
> Despite doing some research online and in electrical engineering books,
> I can't find a figure for the accuracy of the time keeping of the UK
> power grid. Perhaps this is because there aren't official bounds set for
> the time error - one of my electrical engineering books says it is a
> legal requirement that the frequency be kept "as close as possible to 50
> Hz" - but even if this is the case it should be possible to determine a
> typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes every
> 6 months. Does anyone know the typical time error seen on the UK grid,
> or where I might find this information? Any suggestions would be much
> appreciated.
>
> Best wishes,
>
> Chris Tidy
>

Can't say about the UK but in the US the clocks that run only on the power
grid and depend on the frequency are very accurate over a long period of
time. I would say more like less than a minuit or less over a year period
of time if the clock its self is up to it. During periods of peak loads the
nominal 60 hz may go down a cycle or so and when the load is taken away the
power company will raise the frequency long enough to get the clocks back in
time.

In other words the power company keeps the frequency to an average of
exectally 60 hz over a long period of time. Much more stable than any clock
you could build that depends on a quartz chip.

webpa

2006-04-14, 12:21 pm

Christopher Tidy wrote:
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending =A340 buying a programmable
> quartz oscillator chip.
>
> Despite doing some research online and in electrical engineering books,
> I can't find a figure for the accuracy of the time keeping of the UK
> power grid. Perhaps this is because there aren't official bounds set for
> the time error - one of my electrical engineering books says it is a
> legal requirement that the frequency be kept "as close as possible to 50
> Hz" - but even if this is the case it should be possible to determine a
> typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes every
> 6 months. Does anyone know the typical time error seen on the UK grid,
> or where I might find this information? Any suggestions would be much
> appreciated.
>
> Best wishes,
>
> Chris Tidy

Couldn't find anything on the UK grid, but the US grid short-term is
generally 10 milliHz or better and (probably) averages a few
milliseconds per year long-term. Take care to accommodate local line
noise because it can trip digital counters; even cheap consumer digital
clocks sometimes don't use line frequency directly for this reason, but
use a loosely coupled PLL instead.

Tim S

2006-04-14, 12:21 pm

Christopher Tidy wrote:

> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending £40 buying a programmable
> quartz oscillator chip.
>
> Despite doing some research online and in electrical engineering books,
> I can't find a figure for the accuracy of the time keeping of the UK
> power grid. Perhaps this is because there aren't official bounds set for
> the time error - one of my electrical engineering books says it is a
> legal requirement that the frequency be kept "as close as possible to 50
> Hz" - but even if this is the case it should be possible to determine a
> typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes every
> 6 months. Does anyone know the typical time error seen on the UK grid,
> or where I might find this information? Any suggestions would be much
> appreciated.
>
> Best wishes,
>
> Chris Tidy

Used to be the case that frequency was governed to certain tolerances and
number of cycles turned out in a 24 period was mandated to be exactly
50*24*3600, with time keeping in mind.

Not sure what the position is since privitisation.

Tim

Alan J. Wylie

2006-04-14, 12:21 pm

On Fri, 14 Apr 2006 15:27:23 +0000, Christopher Tidy <cdt22NOSPAM@cantabgold.net> said:

> Hi all, I'm thinking of building an electronic clock control circuit
> which uses the 50 Hz mains frequency for time keeping. The reason
> for this is that the clock dial is rather large, so probably
> wouldn't run for long on battery power, and I don't fancy spending
> £40 buying a programmable quartz oscillator chip.

> Despite doing some research online and in electrical engineering
> books, I can't find a figure for the accuracy of the time keeping of
> the UK power grid. Perhaps this is because there aren't official
> bounds set for the time error - one of my electrical engineering
> books says it is a legal requirement that the frequency be kept "as
> close as possible to 50 Hz" - but even if this is the case it should
> be possible to determine a typical error figure.

> From my point of view I'd regard an acceptable error as 5 minutes
> every 6 months. Does anyone know the typical time error seen on the
> UK grid, or where I might find this information? Any suggestions
> would be much appreciated.

<http://www.nationalgrid.com/uk/Elec.../Data/Realtime/>

<http://www.dynamicdemand.co.uk/chart.htm>

During periods of high demand, the frequency will drop slightly. To
compensate, the frequency will later be increased so that there are
the same number of cycles per day, so that the long term accuracy of
synchronous electric clocks is very good. If you don't have a seconds
hand, no-one will even notice the short term inaccuracies.

A quick look at the graphs suggests that the maximum deviation is
about 0.2 / 50 (2.5 seconds in 10 minutes), the period of low
frequency lasts in the order of ten minutes, and corrections are made
immediately after the dip.

--
Alan J. Wylie http://www.wylie.me.uk/
"Perfection [in design] is achieved not when there is nothing left to add,
but rather when there is nothing left to take away."
-- Antoine de Saint-Exupery

Roger Mills

2006-04-14, 12:21 pm

In an earlier contribution to this discussion,
Christopher Tidy <cdt22NOSPAM@cantabgold.net> wrote:

> Hi all,
>
> I'm thinking of building an electronic clock control circuit which
> uses the 50 Hz mains frequency for time keeping. The reason for this
> is that the clock dial is rather large, so probably wouldn't run for
> long on battery power, and I don't fancy spending £40 buying a
> programmable quartz oscillator chip.
>
> Despite doing some research online and in electrical engineering
> books, I can't find a figure for the accuracy of the time keeping of
> the UK power grid. Perhaps this is because there aren't official
> bounds set for the time error - one of my electrical engineering
> books says it is a legal requirement that the frequency be kept "as
> close as possible to 50 Hz" - but even if this is the case it should
> be possible to determine a typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes
> every 6 months. Does anyone know the typical time error seen on the
> UK grid, or where I might find this information? Any suggestions
> would be much appreciated.
>
> Best wishes,
>
> Chris Tidy

My understanding is that the frequency is allowed to fluctuate by a small
amount (don't know how much) but that, over a 24 hour period, exactly the
right number of cycles will be delivered. So your clock should at least be
exactly right once per day.
--
Cheers,
Roger
______
Please reply to newsgroup.
Reply address IS valid, but not regularly monitored.

Ian Stirling

2006-04-14, 12:21 pm

In uk.d-i-y Christopher Tidy <cdt22NOSPAM@cantabgold.net> wrote:
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending ?40 buying a programmable
> quartz oscillator chip.

300s/30Ms = 10ppm.
300s/15Ms = 20ppm.
That's not too taxing.
IIRC, maxim/dallas do some chips that may suit, for way, way less than
40 quid.

Mr Fixit

2006-04-14, 12:21 pm

Bob Eager

2006-04-14, 1:21 pm

On Fri, 14 Apr 2006 15:00:33 UTC, alan@wylie.me.uk (Alan J. Wylie)
wrote:

> During periods of high demand, the frequency will drop slightly. To
> compensate, the frequency will later be increased so that there are
> the same number of cycles per day, so that the long term accuracy of
> synchronous electric clocks is very good. If you don't have a seconds
> hand, no-one will even notice the short term inaccuracies.

As a matter of interest...when you see those pictures of the control
room, there are two clocks near top right. One is grid driven, the other
is 'crystal' driven (probably rather better than that, these days). They
*ought* to read the same...

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

Andrew Mawson

2006-04-14, 1:21 pm

"Christopher Tidy" <cdt22NOSPAM@cantabgold.net> wrote in message
news:443FBF5B.4090101@cantabgold.net...
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which
uses
> the 50 Hz mains frequency for time keeping. The reason for this is
that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending £40 buying a programmable
> quartz oscillator chip.
>
> Despite doing some research online and in electrical engineering
books,
> I can't find a figure for the accuracy of the time keeping of the UK
> power grid. Perhaps this is because there aren't official bounds set
for
> the time error - one of my electrical engineering books says it is a
> legal requirement that the frequency be kept "as close as possible
to 50
> Hz" - but even if this is the case it should be possible to
determine a
> typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes
every
> 6 months. Does anyone know the typical time error seen on the UK
grid,
> or where I might find this information? Any suggestions would be
much
> appreciated.
>
> Best wishes,
>
> Chris Tidy
>

Chris,

OK it's going back a few years, but when the CEGB had their National
Grid Control Centre at Park ST London SE1 the number of cycles per day
was very accurately ensured to be correct (A pair of Ferranti Argus
500 Process Control computers each had an ultra accurate crystal
clocks in them feeding displays in the control room) and the Control
Enginners could let the frequency drift a tad hour by hour but had to
get it right over 24. They dispersed the control to various regional
centres (Winnersh, St Albans and three others I cannot remember but I
think that the principle remains the same.

AWEM
(who in a past life occassionally sweated blood over those computers!)

Jack Denver

2006-04-14, 1:21 pm

It really depends where you are - if you are in a rural area with above
ground lines and lots of ice storms, hurricanes, etc. then not too good. In
an urban area with buried lines, power may go uninterrupted for years at a
time.

If it's critical that the clock not stop you can put it on a UPS battery
backup.

"Mike Berger" <berger@shout.net> wrote in message
news:e1ocb3$u2h$1@roundup.shout.net...[color=darkred]
> In the U.S. the power grid is very accurate over long periods of
> time. But what are the odds of running six months without a single
> power interruption?
>
> Christopher Tidy wrote:
> ...
>

Andy Dingley

2006-04-14, 1:21 pm

On Fri, 14 Apr 2006 15:27:23 +0000, Christopher Tidy
<cdt22NOSPAM@cantabgold.net> wrote:

>I can't find a figure for the accuracy of the time keeping of the UK
>power grid.

It's weird. Frequency is allowed to wobble a bit, but it has to average
out very accurately over 24 hours or so, because of the number of clocks
in service.

Ian Stirling

2006-04-14, 1:21 pm

In uk.d-i-y Christopher Tidy <cdt22NOSPAM@cantabgold.net> wrote:
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending ?40 buying a programmable
> quartz oscillator chip.

I probably should have mentioned.
If this is outside.
You can get GPS, for about that price, and if it's a clockface, you can
mount the antenna there, and have it work just fine.

daestrom

2006-04-14, 1:21 pm

"Ralph Mowery" <rmowery28146@earthlink.net> wrote in message
news:VEO%f.6970$i41.5742@newsread1.news.atl.earthlink.net...
>
> "Christopher Tidy" <cdt22NOSPAM@cantabgold.net> wrote in message
> news:443FBF5B.4090101@cantabgold.net...
>
> Can't say about the UK but in the US the clocks that run only on the power
> grid and depend on the frequency are very accurate over a long period of
> time. I would say more like less than a minuit or less over a year period
> of time if the clock its self is up to it. During periods of peak loads
> the
> nominal 60 hz may go down a cycle or so and when the load is taken away
> the
> power company will raise the frequency long enough to get the clocks back
> in
> time.
>

Well, you got the basic idea right. But it never drifts down 1
cycle/second. Very rarely drops even a tenth of a cycle.

> In other words the power company keeps the frequency to an average of
> exectally 60 hz over a long period of time. Much more stable than any
> clock
> you could build that depends on a quartz chip.
>

Indeed. Part of the standard equipment in the old days was a special
'crystal oven' with tightly controlled temperature. By regulating the
temperature of the crystal inside, the accuracy its vibrations was improved.

An old 'urban lengend' was that the first quartz watches were calibrated
assuming the temperature of the crystal was going to be controlled by the
body heat of the wearer. And that leaving your watch on the dresser over
the week-end would cause it to slow down slightly. Don't know if it is
really true, but it's a nice story.

daestrom

Paul Cooper

2006-04-14, 1:21 pm

On Fri, 14 Apr 2006 15:27:23 +0000, Christopher Tidy
<cdt22NOSPAM@cantabgold.net> wrote:

>Hi all,
>
>I'm thinking of building an electronic clock control circuit which uses
>the 50 Hz mains frequency for time keeping. The reason for this is that
>the clock dial is rather large, so probably wouldn't run for long on
>battery power, and I don't fancy spending £40 buying a programmable
>quartz oscillator chip.
>
>Despite doing some research online and in electrical engineering books,
>I can't find a figure for the accuracy of the time keeping of the UK
>power grid. Perhaps this is because there aren't official bounds set for
>the time error - one of my electrical engineering books says it is a
>legal requirement that the frequency be kept "as close as possible to 50
>Hz" - but even if this is the case it should be possible to determine a
>typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes every
>6 months. Does anyone know the typical time error seen on the UK grid,
>or where I might find this information? Any suggestions would be much
>appreciated.
>
>Best wishes,
>
>Chris Tidy

Other people have given the rules that are applied (i.e. that the
total number of cycles in 24 hours is constant), but the reason is for
efficienty of electricty transfer. It is very important that all
generators run in sync, so as to minimize transmission losses in the
National Grid, AFAIUI.

Paul

Brian Sharrock

2006-04-14, 2:21 pm

"Christopher Tidy" <cdt22NOSPAM@cantabgold.net> wrote in message
news:443FBF5B.4090101@cantabgold.net...

>
> From my point of view I'd regard an acceptable error as 5 minutes every 6
> months. Does anyone know the typical time error seen on the UK grid, or
> where I might find this information? Any suggestions would be much
> appreciated.
>
> Best wishes,
>
> Chris Tidy
>

In the 'old' days; mains powered clocks (squirrel cage, synchronous) were
common.
Many mantel shelves had a two pin round outlet fixed above them for the sole
purposes of plugging in an electric clock.
Although the _instantaneous_ frequency stability of the mains supply is
(relatively) wide; the aggregation of time periods (inverse of frequency)
over the course of the day results in a discrepancy that was/is tiny. IIRC,
power station control rooms had a red finger which was slaved to a
pendulum/GPO time source while the same 'meter' showed the integration of
the 50Hz periods - aka 'Electric Time'. It was a responsibility of the
Control Room staff to keep 'Electric Time' consonant with 'GPO Time': this
could be achieved by altering the instantaneous frequency (speeding up/
slowing down ).

However; as Argos flogs Rugby-synchronised wrist watches for ten-quid-odd,
why bother? PS, the 'Klick' wristwatch not only adapts to GMT/BST changes
but it functions as a depth-gauge: - if it stops working I must be deeper
than fifty feet - but at least I'll have the facility to observe TOD !

--

Brian

Jack Denver

2006-04-14, 2:21 pm

There's nothing "urban legend" about that. To this day, most quartz watch
circuits are not temperature compensated (and obviously there is not enough
power available to put the crystal in an "oven" in a wristwatch) so their
timekeeping will vary slightly based on temperature. Typically a
manufacturer will pick some midpoint between body temperature and room
temperature (I have seen 31C used as at typical #) and use that as the
temperature at which their movements are calibrated at the factory. If the
actual operating conditions vary from that temperature, the watch will drift
slightly from the calibrated rate, but it's no big deal.

"daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
news:ELP%f.1182$kz3.377@twister.nyroc.rr.com...
>
>
> An old 'urban lengend' was that the first quartz watches were calibrated
> assuming the temperature of the crystal was going to be controlled by the
> body heat of the wearer. And that leaving your watch on the dresser over
> the week-end would cause it to slow down slightly. Don't know if it is
> really true, but it's a nice story.
>
> daestrom
>

raden

2006-04-14, 2:21 pm

In message <443FBF5B.4090101@cantabgold.net>, Christopher Tidy
<cdt22NOSPAM@cantabgold.net> writes
>Hi all,
>
>I'm thinking of building an electronic clock control circuit which uses
>the 50 Hz mains frequency for time keeping. The reason for this is that
>the clock dial is rather large, so probably wouldn't run for long on
>battery power, and I don't fancy spending £40 buying a programmable
>quartz oscillator chip.
>
>
>From my point of view I'd regard an acceptable error as 5 minutes every
>6 months. Does anyone know the typical time error seen on the UK grid,
>or where I might find this information? Any suggestions would be much
>appreciated.
>
It has to be significantly more accurate than that

Power stations have to be in sync with one another - which requires good
accuracy and stability

--
geoff

JANA

2006-04-14, 2:21 pm

For any type of accuracy, depending on the power grid is not a dependable
option! There can be noise, interference, and power dips. On the short
term, the power grid will be accurate, but over the long term, it can be out
by a fair amount.

I have an electric clock that is dependent on the power grid for its timing.
This clock can be a few minutes or a few seconds out at times.This is not
from the power company being off frequency. It is most likely caused by
power dips, or noise in the power delivery.

The accuracy of the power companies timing is very accuracy. It has to be in
order to keep synchronized to other systems that they are working with. They
have many generating facilities that are working together, therefore all
their systems have to be synchronized to within fractions of a degree on the
line frequency. From what I am told, here in North America, their margin of
error is within about
1 second per month.

The problem when connecting a device at home to the
power line, such as a clock, the clock can jump off time very easily. It is
susceptible to interference, and power disturbance through their
distribution. I was also told this by an engineer from our local power
company.

Normally, during peak conditions, they allow the frequency to drop very
slightly. It may be as much as 0.5 to 1 Hertz or so. During peak conditions,
they will give it back. This means that all the power generation systems
working together must also drop, and increase by the same amount.

The clocks that I have that are referenced to the AC line, are not
dependable for accurate time. Over a few weeks, I found the quartz clocks to
be more accurate. I can check them with the NIST broadcast.

Here in North America many stores are selling quartz clocks with built in
time receivers. These are getting the time reference from the NIST. The user
only has to put in the approximate time to within about 30 minutes. After 12
hours, the clock will be exactly on time, as long as it can receive the NIST
signal. The clock automatically checks in with the NIST about every 12
hours. If the NIST signal is unavailable, the clock will keep time to the
spec of any consumer type quartz clock. This is about 5 to 10 seconds per
month.

Another thought would be to get a low cost GPS that can accept an external
antenna and external power supply. This will give you the most accurate
possible time for home use.

You can also go to the NIST site with your computer, and get very accurate
time. It should be within about 100 to 200 ms. Going from memory, I believe
it will tell you its error to your computer. By hitting the reset key, you
can sometimes get it down to within a few milliseconds.

--

JANA
_____

"Christopher Tidy" <cdt22NOSPAM@cantabgold.net> wrote in message
news:443FBF5B.4090101@cantabgold.net...
Hi all,

I'm thinking of building an electronic clock control circuit which uses
the 50 Hz mains frequency for time keeping. The reason for this is that
the clock dial is rather large, so probably wouldn't run for long on
battery power, and I don't fancy spending £40 buying a programmable
quartz oscillator chip.

Despite doing some research online and in electrical engineering books,
I can't find a figure for the accuracy of the time keeping of the UK
power grid. Perhaps this is because there aren't official bounds set for
the time error - one of my electrical engineering books says it is a
legal requirement that the frequency be kept "as close as possible to 50
Hz" - but even if this is the case it should be possible to determine a
typical error figure.

From my point of view I'd regard an acceptable error as 5 minutes every
6 months. Does anyone know the typical time error seen on the UK grid,
or where I might find this information? Any suggestions would be much
appreciated.

Best wishes,

Chris Tidy

JANA

2006-04-14, 2:21 pm

The older consumer quartz wrist watches were a little temperature sensitive.
Wearing them could effect their accuracy a little. Whether or not it went
faster or slower, depended on the temperature coefficiency of the particular
quartz crystal and components in the watch and how the local oscillator in
the watch was designed. The manufactures of the higher end watches tried to
have their calibration set up for the watch to be at the average body
surface temperature for approximately 14 hours per day, and at room
temperature for approximately 10 hours per day.

The newer watches are improved to a great extent. Many of the new watches
will keep an average time of better than about 5 to 8 seconds per month.
There are some very expensive models where they will guarantee an average
accuracy of better than 2 to 5 seconds per month. The older watches going
back more than about 8 to 10 years ago were usually not much better than 15
to 20 seconds per month.

--

JANA
_____

"daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
news:ELP%f.1182$kz3.377@twister.nyroc.rr.com...

"Ralph Mowery" <rmowery28146@earthlink.net> wrote in message
news:VEO%f.6970$i41.5742@newsread1.news.atl.earthlink.net...
>
> "Christopher Tidy" <cdt22NOSPAM@cantabgold.net> wrote in message
> news:443FBF5B.4090101@cantabgold.net...
>
> Can't say about the UK but in the US the clocks that run only on the power
> grid and depend on the frequency are very accurate over a long period of
> time. I would say more like less than a minuit or less over a year period
> of time if the clock its self is up to it. During periods of peak loads
> the
> nominal 60 hz may go down a cycle or so and when the load is taken away
> the
> power company will raise the frequency long enough to get the clocks back
> in
> time.
>

Well, you got the basic idea right. But it never drifts down 1
cycle/second. Very rarely drops even a tenth of a cycle.

> In other words the power company keeps the frequency to an average of
> exectally 60 hz over a long period of time. Much more stable than any
> clock
> you could build that depends on a quartz chip.
>

Indeed. Part of the standard equipment in the old days was a special
'crystal oven' with tightly controlled temperature. By regulating the
temperature of the crystal inside, the accuracy its vibrations was improved.

An old 'urban lengend' was that the first quartz watches were calibrated
assuming the temperature of the crystal was going to be controlled by the
body heat of the wearer. And that leaving your watch on the dresser over
the week-end would cause it to slow down slightly. Don't know if it is
really true, but it's a nice story.

daestrom

Mooron

2006-04-14, 2:21 pm

Ralph Mowery wrote:

> Can't say about the UK but in the US the clocks that run only on the power
> grid and depend on the frequency are very accurate over a long period of
> time. I would say more like less than a minuit or less over a year period
> of time if the clock its self is up to it. During periods of peak loads the
> nominal 60 hz may go down a cycle or so and when the load is taken away the
> power company will raise the frequency long enough to get the clocks back in
> time.

I read an article a few years ago that discussed how the frequency is
regulated in the US. I can't find it now. I think it was by David
Mills
from the university of Delaware. As I reacall, there are 2 power grids
in the US. The Eastern grid is controlled by an automated system
at some power plant in Ohio. The Western grid is controlled manually.
I wish I could find the article, it had some interesting stuff.

Things are probably done in a similar fashion in the UK.

- Mooron

Ian Stirling

2006-04-14, 2:21 pm

In uk.d-i-y raden <raden@kateda.org> wrote:
> In message <443FBF5B.4090101@cantabgold.net>, Christopher Tidy
> <cdt22NOSPAM@cantabgold.net> writes
> It has to be significantly more accurate than that
>
> Power stations have to be in sync with one another - which requires good
> accuracy and stability

Actually not - the power grid will work just fine at 49.7Hz average.
The way that large generators work, at all times other than when you're
starting one up, they are fixed to the grid frequency.
If you try to turn one harder, it just generates more electricity, and
tends to 'push' the whole system higher in frequency.
Of course, one generator can't do this appreciably.

There is no actual need for a national centralised frequency
setting, because of the way it works, as long as some power stations
switch off/on up/down, when the frequency gets above or below 50Hz.
This can be done fine with a 48-52Hz analog meter in the control rooms
of each power station.

Dave (from the UK)

2006-04-14, 4:21 pm

Christopher Tidy wrote:
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending £40 buying a programmable
> quartz oscillator chip.
>
> Despite doing some research online and in electrical engineering books,
> I can't find a figure for the accuracy of the time keeping of the UK
> power grid. Perhaps this is because there aren't official bounds set for
> the time error - one of my electrical engineering books says it is a
> legal requirement that the frequency be kept "as close as possible to 50
> Hz" - but even if this is the case it should be possible to determine a
> typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes every
> 6 months. Does anyone know the typical time error seen on the UK grid,
> or where I might find this information? Any suggestions would be much
> appreciated.
>
> Best wishes,
>
> Chris Tidy
>

Try asking on time-nuts

http://www.leapsecond.com/time-nuts.htm

--
Dave K MCSE.

MCSE = Minefield Consultant and Solitaire Expert.

Please note my email address changes periodically to avoid spam.
It is always of the form: month-year@domain. Hitting reply will work
for a couple of months only. Later set it manually.

Don Kelly

2006-04-14, 4:21 pm

"JANA" <jana@ca.inter.net> wrote in message
news:4aa267Fs1jmfU2@uni-berlin.de...
> For any type of accuracy, depending on the power grid is not a dependable
> option! There can be noise, interference, and power dips. On the short
> term, the power grid will be accurate, but over the long term, it can be
> out
> by a fair amount.
----------------
In fact, long term accuracy is very good- correction is made to ensure that.
Short term accuracy may drift but is regularly compensated for. One system
that I know had corrections made every minute. Nice homegrown control but
wasn't compatible with the overall system when the utility joined the
Western Grid.
----------
>
> I have an electric clock that is dependent on the power grid for its
> timing.
> This clock can be a few minutes or a few seconds out at times.This is not
> from the power company being off frequency. It is most likely caused by
> power dips, or noise in the power delivery.
-------
And how is this clock driven? If it is a digital clock or electronic then
your point may be valid.
If it has a hysteresis synchronous motor then it will depend strictly on the
frequency and not noise or "dips". However, these may be hard to find
nowadays.
--------
>
> The accuracy of the power companies timing is very accuracy. It has to be
> in
> order to keep synchronized to other systems that they are working with.
> They
> have many generating facilities that are working together, therefore all
> their systems have to be synchronized to within fractions of a degree on
> the
> line frequency. From what I am told, here in North America, their margin
> of
> error is within about
> 1 second per month.
------------
All machines on the system will be synchronised - at the same frequency- and
drifting up and down together if frequency is changing. You will not have
frequency differences between machines on a system. There are variations in
phase but anything that can be measured as a frequency change -can't be- as
by then the system is unstable and it is lights out. ( if one machine is
0.01Hz fast or slow, then instability can occur in less than a second. )
It appears that you are referring to the process of connecting a machine to
the system and doing this smoothly does require being within a few degrees
in phase and only a small frequency difference in order to minimise "bumps"
and heavy power surges when the system pulls the machine into full
synchronism. This, of course, has nothing to do with control of time.
------------

> The problem when connecting a device at home to the
> power line, such as a clock, the clock can jump off time very easily. It
> is
> susceptible to interference, and power disturbance through their
> distribution. I was also told this by an engineer from our local power
> company.
---------
Depending on how the clock is driven as indicated above.
----
>
> Normally, during peak conditions, they allow the frequency to drop very
> slightly. It may be as much as 0.5 to 1 Hertz or so. During peak
> conditions,
> they will give it back. This means that all the power generation systems
> working together must also drop, and increase by the same amount.
---------
Daestrom had it right. In fact a drop of 0.5Hz is abnormal and is an
incident that should be looked into. 0.05 Hz is more typical.
There is a reason for "allowing the frequency to change" when load changes.
It is deliberately built into the prime mover governors. This droop allows
proper power sharing between machines. An overall system control then
adjusts all machines to bring the frequency back to normal or to make
necessary time corrections (Load-frequency control).
>
> The clocks that I have that are referenced to the AC line, are not
> dependable for accurate time. Over a few weeks, I found the quartz clocks
> to
> be more accurate. I can check them with the NIST broadcast.
..>
> Here in North America many stores are selling quartz clocks with built in
> time receivers. These are getting the time reference from the NIST. The
> user
> only has to put in the approximate time to within about 30 minutes. After
> 12
> hours, the clock will be exactly on time, as long as it can receive the
> NIST
> signal. The clock automatically checks in with the NIST about every 12
> hours. If the NIST signal is unavailable, the clock will keep time to the
> spec of any consumer type quartz clock. This is about 5 to 10 seconds per
> month.
-----------
As far as I know, the utilities compare to NIST and make corrections on a
much more frequent basis. There is also a contradiction with what you said
above "From what I am told, here in North America, their margin of
> error is within about
> 1 second per month."

That sounds better than 5 to 10 seconds per month.

I think the problem may be with the way your clock is driven, not with the
time error of the grid.
--

Don Kelly @shawcross.ca
remove the X to answer
----------------------------

>
> Another thought would be to get a low cost GPS that can accept an external
> antenna and external power supply. This will give you the most accurate
> possible time for home use.
>
> You can also go to the NIST site with your computer, and get very accurate
> time. It should be within about 100 to 200 ms. Going from memory, I
> believe
> it will tell you its error to your computer. By hitting the reset key, you
> can sometimes get it down to within a few milliseconds.
>
> --
>
> JANA
> _____
>
>
> "Christopher Tidy" <cdt22NOSPAM@cantabgold.net> wrote in message
> news:443FBF5B.4090101@cantabgold.net...
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending £40 buying a programmable
> quartz oscillator chip.
>
> Despite doing some research online and in electrical engineering books,
> I can't find a figure for the accuracy of the time keeping of the UK
> power grid. Perhaps this is because there aren't official bounds set for
> the time error - one of my electrical engineering books says it is a
> legal requirement that the frequency be kept "as close as possible to 50
> Hz" - but even if this is the case it should be possible to determine a
> typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes every
> 6 months. Does anyone know the typical time error seen on the UK grid,
> or where I might find this information? Any suggestions would be much
> appreciated.
>
> Best wishes,
>
> Chris Tidy
>
>
>

Mathew Newton

2006-04-14, 4:21 pm

Roger Mills wrote:

> My understanding is that the frequency is allowed to fluctuate by a small
> amount (don't know how much) but that, over a 24 hour period, exactly the
> right number of cycles will be delivered. So your clock should at least be
> exactly right once per day.

Even a stopped clock doubles that... ;-)

Mathew

Andy Dingley

2006-04-14, 4:21 pm

On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
<b.sharrock@ntlworld.com> wrote:

>In the 'old' days; mains powered clocks (squirrel cage, synchronous) were
>common.

Although a squirrel cage uses a synchronous stator winding, it isn't a
synchronous motor, at least not to this level of timekeeping. Their
rotors are powered by an induced current in the rotor (the squirrel cage
itself), not any sliprings or brushgear. This current is only induced if
the rotor experiences a moving or changing magnetic field - i.e. it
rotates at a different speed to the field in the stator. They can't
generate a torque unless there is some "slip", the speed difference
between synchronous speed and actual rotation. It's notable that the
more the slip, the more the output torque - so these motors can deliver
substantial power under load.

A frictionless, resistanceless, hysteresisless squirrel cage motor doing
no work would accelerate up to synchronous speed and then hold that
speed spinning freely, doing no work and producing no torque. An
idealised but possible motor might always run at a known slip which
could be compensated for by gearing. In practice such effects as
temperature and lubricant viscosity make this unpredictable, at least
for clockmaking accuracy.

Clocks use shaded pole motors, which are synchronous. As these don't
have the same increased torque response to slip they're inherently low
torque and thus only useful for clocks or other light tasks.

Don Kelly

2006-04-14, 5:21 pm

Correction and apology:
I said: ( if one machine is
> 0.01Hz fast or slow, then instability can occur in less than a second. )

That is wrong. 3.6 degrees/second implies about <25 seconds to steady state
instability. This is , of course, too simplistic as such a sustained
frequency difference will not occur - either the errant machine is pulled
back into synchronism or has been tripped out -hopefully without bringing
the whole system down.

This also applies to incoming machines- either they get in line or get
kicked out-now!.
--

Don Kelly @shawcross.ca
remove the X to answer
----------------------------

Mike Barnes

2006-04-14, 5:21 pm

In uk.d-i-y, Christopher Tidy wrote:
>I'm thinking of building an electronic clock control circuit which uses
>the 50 Hz mains frequency for time keeping. The reason for this is that
>the clock dial is rather large, so probably wouldn't run for long on
>battery power, and I don't fancy spending £40 buying a programmable
>quartz oscillator chip.

I'd be tempted to use a wall-wart instead of a battery, and probably an
MSF mechanism if it was strong enough.

--
Mike Barnes

Andy Dingley

2006-04-14, 5:21 pm

On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
<b.sharrock@ntlworld.com> wrote:

>In the 'old' days; mains powered clocks (squirrel cage, synchronous) were
>common.

This is Usenet isn't it? There'll be complaints....

Of course not all clock motors are shaded pole. The Warren Model A was,
back in 1916 (I think the first synchronous clock motor)

However the well-known Westclox / Sangamo design of the '30s and onwards
used an induction rotor - effectively a "squirrel cage". This gave good
starting torque, but obviously had the slip problem. To keep it locked
and synchronous there was also a permanent magnet rotor. This gave
adequate torque at synchronous speed, without slip, but wouldn't have
been able to start the clock unaided.

Some British designs used a single permanent magnet rotor and required a
mechanical pushbutton, or an extra winding for starting.

Derek ^

2006-04-14, 5:21 pm

On Fri, 14 Apr 2006 16:50:40 GMT, raden <raden@kateda.org> wrote:

>In message <443FBF5B.4090101@cantabgold.net>, Christopher Tidy
><cdt22NOSPAM@cantabgold.net> writes

There won't be any cumulative errors.
[color=darkred]
>It has to be significantly more accurate than that
>
>Power stations have to be in sync with one another - which requires good
>accuracy and stability

True they have to be phased up to the grid exactly before they connect
to it, or *BANG* turbine blades through the turbine hall roof. I've
been to a power station where it had happened. If they connect
successfully then they'll stay in sync.

The exact frequency is not overly critical but is kept as accurate as
possible for the benefit of users who depend on the frequency being
accurate, steelmills rolling steel for instance.

FWIR the control console at "Grid Control Centres" used to have a
standard synchronous electric clock showing grid time, and a clock
showing exact GMT (How ??, unless exact 50Hz was distributed about the
country) . It was normal for "grid time" to lose a bit during the day,
depending on load, and then make up for it overnight.

Quite a manual process in 1969. ;-)

It must be better now !

DG

Edgar Iredale

2006-04-14, 6:21 pm

Andy Dingley wrote:

> On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
> <b.sharrock@ntlworld.com> wrote:
>
>
> This is Usenet isn't it? There'll be complaints....
>
> Of course not all clock motors are shaded pole. The Warren Model A
> was, back in 1916 (I think the first synchronous clock motor)
>
> However the well-known Westclox / Sangamo design of the '30s and
> onwards
> used an induction rotor - effectively a "squirrel cage". This gave
> good starting torque, but obviously had the slip problem. To keep it
> locked and synchronous there was also a permanent magnet rotor. This
> gave adequate torque at synchronous speed, without slip, but wouldn't
> have been able to start the clock unaided.
>
> Some British designs used a single permanent magnet rotor and required
> a mechanical pushbutton, or an extra winding for starting.

I have an old Smith Sectric electric clock that was, I think, new in
1942. It maintains time accurately as compared with a radio clock, so
long as the power doesn't fail. When I was very young I remember being
the only person in the house who could get it going again after a power
cut. One was supposed to set the time and jab in the setting knob to
start it, but that seldom worked. At about the age of five I discovered
the best way was to remove the motor cover and spin the wheels inside.

Edgar

Mark and Gloria Hagwood

2006-04-14, 6:21 pm

Jack Denver wrote:
> It really depends where you are - if you are in a rural area with above
> ground lines and lots of ice storms, hurricanes, etc. then not too good. In
> an urban area with buried lines, power may go uninterrupted for years at a
> time.
>
> If it's critical that the clock not stop you can put it on a UPS battery
> backup.
>
Interesting thought. Would the clock then be driven by the
line frequency or the oscillator frequency of the UPS?

Mark

Michael A. Terrell

2006-04-14, 7:21 pm

Mathew Newton wrote:
>
> Roger Mills wrote:
>
>
> Even a stopped clock doubles that... ;-)
>
> Mathew

Not if it's digital.

--
HELP! My sig file has escaped! ;-)

Andrew Gabriel

2006-04-14, 7:21 pm

In article <nYGdncancI2pIKLZRVnyiQ@bt.com>,
"Andrew Mawson" <andrew@no_spam_please_mawson.org.uk> writes:
> Chris,
>
> OK it's going back a few years, but when the CEGB had their National
> Grid Control Centre at Park ST London SE1 the number of cycles per day
> was very accurately ensured to be correct (A pair of Ferranti Argus
> 500 Process Control computers each had an ultra accurate crystal
> clocks in them feeding displays in the control room) and the Control
> Enginners could let the frequency drift a tad hour by hour but had to
> get it right over 24. They dispersed the control to various regional
> centres (Winnersh, St Albans and three others I cannot remember but I
> think that the principle remains the same.

I'm out of touch now, but CEGB used to keep UK power grid at
50Hz +- 0.1Hz. No one ever came up with a good reason it had
to be that accurate, but they did it "just because they
could", to quote someone I spoke with at the Winnersh control
room about this some years back.

I wrote a more detailed article about this a few years ago,
which discusses various notable historic events, like how the
power grid had to handle the majority of the UK using the toilet
at the same instant, which resulted in the largest ever surge in
demand on the UK power grid (which with advanced planning, it
handled just fine)...
http://groups.google.com/group/sci....11a4f753?hl=en&

--
Andrew Gabriel

Michael A. Terrell

2006-04-14, 7:21 pm

Andrew Mawson wrote:
>
> OK it's going back a few years, but when the CEGB had their National
> Grid Control Centre at Park ST London SE1 the number of cycles per day
> was very accurately ensured to be correct (A pair of Ferranti Argus
> 500 Process Control computers each had an ultra accurate crystal
> clocks in them feeding displays in the control room) and the Control
> Enginners could let the frequency drift a tad hour by hour but had to
> get it right over 24. They dispersed the control to various regional
> centres (Winnersh, St Albans and three others I cannot remember but I
> think that the principle remains the same.
>
> AWEM
> (who in a past life occassionally sweated blood over those computers!)

If all those areas are connected to a single power grid they still
have to stay in sync, even if the control system is broken into regional
centers.

--
HELP! My sig file has escaped! ;-)

Michael A. Terrell

2006-04-14, 7:21 pm

Paul Cooper wrote:
>
> Other people have given the rules that are applied (i.e. that the
> total number of cycles in 24 hours is constant), but the reason is for
> efficienty of electricty transfer. It is very important that all
> generators run in sync, so as to minimize transmission losses in the
> National Grid, AFAIUI.
>
> Paul

Any generator that is not in sync with the grid will either be slowed
down by higher current loading, or it will become a motor and catch up
to the other units. The speed AND phase of a generator has to match the
grid before it can be connected, or it can literally be ripped loose
from its mounts and destroyed. The basic system to do this is a set of
lamps connected between the two generators. The new generator has it
speed slowly adjusted till the brightness is cycling VERY slowly, then
at a time when all the lamps are out it is switched into the grid.
After it is connected it synchs itself completely, then the operator
increases the fuel or water supply to generate electricity. This has to
be monitored to keep the generator below it rated output, to keep the
windings from overheating.

--
HELP! My sig file has escaped! ;-)

Jack Denver

2006-04-14, 7:21 pm

The latter during power cuts, the former the rest of the time, the way most
UPS's are designed.

"Mark and Gloria Hagwood" <Nobody@cox.net> wrote in message
news:fLT%f.41355$bm6.26995@fed1read04...
> Interesting thought. Would the clock then be driven by the line frequency
> or the oscillator frequency of the UPS?
>
> Mark

Michael A. Terrell

2006-04-14, 8:21 pm

Andrew Gabriel wrote:
>
> I'm out of touch now, but CEGB used to keep UK power grid at
> 50Hz +- 0.1Hz. No one ever came up with a good reason it had
> to be that accurate, but they did it "just because they
> could", to quote someone I spoke with at the Winnersh control
> room about this some years back.

.1 Hz is not an unreasonable standard to keep. The wider the
variation that is allowed in the control loop, the easier for the whole
system to become unstable and shut down as the controls disconnected
equipment from the grid that was too fast, or too slow. You are working
with massive mechanical systems that will self destruct if you allow
sudden changes while under load. Think of what happens when a long
train tries to stop. If the couplings didn't have some play to adsorb
the shot, the train would derail when the engineer tried to use the
brakes. Its just basic physics.

--
HELP! My sig file has escaped! ;-)

Christopher Tidy

2006-04-14, 9:21 pm

Hi all,

Thanks very much for all the information. Sorry for the original
cross-post; I was expecting very few replies.

In answer to some of your questions, the clock is a WWII German
"Dehomag" slave clock, originally designed to be driven by a master
clock. It has no second hand. The minute hand appears to be balanced,
but the hour hand not. The clock is about 14" across, so not huge, but
it's exceptionally heavy as nearly everything is made from 1 mm steel
plate. Here's a picture of the clock:

http://www.mythic-beasts.com/~cdt22/dehomag.jpg

I can't decide whether to repaint it black, as it was when manufactured,
or to leave it grey. It's for my bedroom, so if it were to stop during
power cuts I wouldn't mind. It sounds like the 50 Hz grid frequency will
be a plenty accurate time keeping source, and it's an interesting
solution to the problem. We live in a pretty rural area so I'll try to
design a circuit which will be fairly resistant to noise. I had already
planned to put a Schmitt trigger on the input from the step-down
transformer.

Once again, thanks for all the advice. It's much more than I got from
the National Grid - the phone number on their website doesn't even work!

Best wishes,

Chris

John G

2006-04-15, 12:21 am

"Christopher Tidy" <cdt22NOSPAM@cantabgold.net> wrote in message
news:44404206.3020807@cantabgold.net...
> Hi all,
>
> Thanks very much for all the information. Sorry for the original
> cross-post; I was expecting very few replies.
>
> In answer to some of your questions, the clock is a WWII German
> "Dehomag" slave clock, originally designed to be driven by a master
> clock. It has no second hand. The minute hand appears to be balanced,
> but the hour hand not. The clock is about 14" across, so not huge, but
> it's exceptionally heavy as nearly everything is made from 1 mm steel
> plate. Here's a picture of the clock:
>
> http://www.mythic-beasts.com/~cdt22/dehomag.jpg
>
> I can't decide whether to repaint it black, as it was when
> manufactured, or to leave it grey. It's for my bedroom, so if it were
> to stop during power cuts I wouldn't mind. It sounds like the 50 Hz
> grid frequency will be a plenty accurate time keeping source, and it's
> an interesting solution to the problem. We live in a pretty rural area
> so I'll try to design a circuit which will be fairly resistant to
> noise. I had already planned to put a Schmitt trigger on the input
> from the step-down transformer.
>
> Once again, thanks for all the advice. It's much more than I got from
> the National Grid - the phone number on their website doesn't even
> work!
>
> Best wishes,
>
> Chris
You did not tell us what the drive mechanism is.
If it was similar to the Simplex/IBM master clocks of the time it most
likely advanced every minute by a pulse to an electromagnet.

Now there are several ways you could generate that.
A Small timer motor with a cam like a washing machine timer.
Or an Electronic cct synched by the mains.

If it is for your bedroom you may not want it after the first few hours
as the electromagnet noise will drive you bonkers.
--
John G

Wot's Your Real Problem?

James Sweet

2006-04-15, 1:21 am

Mike Berger wrote:
> In the U.S. the power grid is very accurate over long periods of
> time. But what are the odds of running six months without a single
> power interruption?
>

Depends where you are, I used to have outages a couple times a year, now
the house I'm in I've had exactly one outage in almost 2 years and it
was a pretty good storm that went through.

Aside from that though in both the US and UK the mains frequency has
excellent long term stability. It may gain or lose a few seconds over
the course of the day but it will be dead on over weeks/months.

Olaf Peuss

2006-04-15, 1:21 am

Jack Denver schrieb:

> If it's critical that the clock not stop you can put it on a UPS battery
> backup.

Great idea! In order to save the odd $40 for a quartz oscillator (read
the OP!), you spend at least $100 on a UPS device. :-)

SCNR and best regards,
OP

Christopher Tidy

2006-04-15, 1:21 am

John G wrote:

<snip>

> You did not tell us what the drive mechanism is.

I did but you probably missed it in my second post. It's a stepper
motor, as I believe is common on many slave dials made in continental
Europe, but relatively uncommon in the UK.

> If it is for your bedroom you may not want it after the first few hours
> as the electromagnet noise will drive you bonkers.

The noise is almost all produced by a ratchet which prevents reverse
rotation of the rotor. It isn't quite as disturbing as the "clunk-click"
of the Gent mechanisms - it's more of a muffled "kerthunk".

Chris

n cook

2006-04-15, 4:21 am

Christopher Tidy <cdt22NOSPAM@cantabgold.net> wrote in message
news:443FBF5B.4090101@cantabgold.net...
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending £40 buying a programmable
> quartz oscillator chip.
>
> Despite doing some research online and in electrical engineering books,
> I can't find a figure for the accuracy of the time keeping of the UK
> power grid. Perhaps this is because there aren't official bounds set for
> the time error - one of my electrical engineering books says it is a
> legal requirement that the frequency be kept "as close as possible to 50
> Hz" - but even if this is the case it should be possible to determine a
> typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes every
> 6 months. Does anyone know the typical time error seen on the UK grid,
> or where I might find this information? Any suggestions would be much
> appreciated.
>
> Best wishes,
>
> Chris Tidy
>

Some future use for the dips in mains frequency use to reduce National Grid
load
http://www.publications.parliament....vn/lds06/text/6
0324-07.htm
starting at heading
Dynamic Demand Appliances Bill [HL]

" Dynamic demand appliances contain a low-cost electronic microcontroller.
This listens to the mains hum, which runs at a frequency of around 50 hertz.
The signal can be detected through every plug socket connected to the
national electricity supply. Through this signal, the dynamic demand
appliances can sense whether the National Grid is under stress and adjust
the time at which they use electricity. The technology is suitable for
appliances that already switch on and off during the day on a "duty cycle",
such as domestic and industrial fridges, freezers and water heaters.

Millions of such appliances acting together would smooth out demand for
electricity. "
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Alan J. Wylie

2006-04-15, 5:21 am

On 14 Apr 2006 21:53:18 GMT, andrew@cucumber.demon.co.uk (Andrew Gabriel) said:

> I wrote a more detailed article about this a few years ago, which
> discusses various notable historic events, like how the power grid
> had to handle the majority of the UK using the toilet at the same
> instant, which resulted in the largest ever surge in demand on the
> UK power grid (which with advanced planning, it handled just
> fine)...
> http://groups.google.com/group/sci....11a4f753?hl=en&

You mention Dinorwic/Dinorwig - there's a more detailed posting about
it at

<http://groups.google.com/group/uk.r...d48c794775000bf>

--
Alan J. Wylie http://www.wylie.me.uk/
"Perfection [in design] is achieved not when there is nothing left to add,
but rather when there is nothing left to take away."
-- Antoine de Saint-Exupery

Doki

2006-04-15, 5:21 am

"daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com> wrote in message
news:ELP%f.1182$kz3.377@twister.nyroc.rr.com...

>
> Indeed. Part of the standard equipment in the old days was a special
> 'crystal oven' with tightly controlled temperature. By regulating the
> temperature of the crystal inside, the accuracy its vibrations was
> improved.
>
> An old 'urban lengend' was that the first quartz watches were calibrated
> assuming the temperature of the crystal was going to be controlled by the
> body heat of the wearer. And that leaving your watch on the dresser over
> the week-end would cause it to slow down slightly. Don't know if it is
> really true, but it's a nice story.

My cheap and nasty Casio digital watch seems to have lost 2 minutes after I
left it first in my old car, and then in my old car in the shed. Neither
place was particularly warm...

Rob Morley

2006-04-15, 8:21 am

In article <443FBF5B.4090101@cantabgold.net>
Christopher Tidy <cdt22NOSPAM@cantabgold.net> wrote:
> Hi all,
>=20
> I'm thinking of building an electronic clock control circuit which uses=
=20
> the 50 Hz mains frequency for time keeping. The reason for this is that=
=20
> the clock dial is rather large, so probably wouldn't run for long on=20
> battery power, and I don't fancy spending =A340 buying a programmable=20
> quartz oscillator chip.
>=20
> Despite doing some research online and in electrical engineering books,=
=20
> I can't find a figure for the accuracy of the time keeping of the UK=20
> power grid. Perhaps this is because there aren't official bounds set for=
=20
> the time error - one of my electrical engineering books says it is a=20
> legal requirement that the frequency be kept "as close as possible to 50=
=20
> Hz" - but even if this is the case it should be possible to determine a=
=20
> typical error figure.
>=20
> From my point of view I'd regard an acceptable error as 5 minutes every=
=20
> 6 months. Does anyone know the typical time error seen on the UK grid,=20
> or where I might find this information? Any suggestions would be much=20
> appreciated.
>=20
I have a vintage synchronous clock which seems to keep good time over a=20
period of months.

Andrew Sinclair

2006-04-15, 10:21 am

In message <e1q6i1$kdf$1@inews.gazeta.pl>, n cook <diverse8@gazeta.pl>
writes
>Some future use for the dips in mains frequency use to reduce National Grid
>load
>http://www.publications.parliament....vn/lds06/text/6
>0324-07.htm
>starting at heading
>Dynamic Demand Appliances Bill [HL]
>
>" Dynamic demand appliances contain a low-cost electronic microcontroller.
>This listens to the mains hum, which runs at a frequency of around 50 hertz.
>The signal can be detected through every plug socket connected to the
>national electricity supply. Through this signal, the dynamic demand
>appliances can sense whether the National Grid is under stress and adjust
>the time at which they use electricity. The technology is suitable for
>appliances that already switch on and off during the day on a "duty cycle",
>such as domestic and industrial fridges, freezers and water heaters.
>
>Millions of such appliances acting together would smooth out demand for
>electricity. "

Have a look here - an on-line frequency monitor.

http://www.dynamicdemand.co.uk/grid.htm

The rest of the website covers the topic of dynamic demand control which
is quite interesting (well it is if you work, as I do, for the company
that owns 70% of Dinorwig).

Andy
--
Andrew Sinclair http://www.smellycat.org

Andy Wade

2006-04-15, 11:21 am

Christopher Tidy wrote:

> From my point of view I'd regard an acceptable error as 5 minutes every
> 6 months. Does anyone know the typical time error seen on the UK grid,
> or where I might find this information? Any suggestions would be much
> appreciated.

You can download more information than you ever wanted to know about the
National Grid from here:

http://www.nationalgrid.com/uk/Elec...e/gridcodedocs/

I've pasted two relevant snippets below (NGET stands for National Grid
Electricity Transmission plc).

1. From the definitions:

Target Frequency
----------------
That Frequency determined by NGET, in its reasonable opinion, as the
desired operating Frequency of the Total System. This will normally
be 50.00Hz plus or minus 0.05Hz, except in exceptional circumstances
as determined by NGET, in its reasonable opinion when this may be
49.90 or 50.10Hz. An example of exceptional circumstances may be
difficulties caused in operating the System during disputes affecting
fuel supplies.

2. From document BC3, which deals with the frequency control process:

BC3.4.3 Electric Time
---------------------
NGET will endeavour (in so far as it is able) to control electric
clock time to within plus or minus 10 seconds by specifying changes
to Target Frequency, by accepting bids and offers in the Balancing
Mechanism. Errors greater than plus or minus 10 seconds may be
temporarily accepted at NGET's reasonable discretion.

All very well, but ISTM that the biggest problem with using the mains
alone as a time standard is power cuts, after which you'll always need
some absolute standard such as MSF, GTS, NTP, etc. to reset your clock.

--
Andy

n cook

2006-04-15, 11:21 am

Andrew Sinclair <news08@smellycat.org> wrote in message
news:P9of0+C0dOQEFwpX@smellycat.org...
> In message <e1q6i1$kdf$1@inews.gazeta.pl>, n cook <diverse8@gazeta.pl>
> writes
Grid[color=darkred]
>
>http://www.publications.parliament....dvn/lds06/text/
6
microcontroller.[color=darkred]
hertz.[color=darkred]
cycle",[color=darkred]
>
> Have a look here - an on-line frequency monitor.
>
> http://www.dynamicdemand.co.uk/grid.htm
>
> The rest of the website covers the topic of dynamic demand control which
> is quite interesting (well it is if you work, as I do, for the company
> that owns 70% of Dinorwig).
>
> Andy
> --
> Andrew Sinclair http://www.smellycat.org

What a swiz, I wanted to see what the real time meter would do at 19.15
tonight

Reason

V

V

V

V

V

V

Dr Who returns

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Derek ^

2006-04-15, 3:21 pm

On Sat, 15 Apr 2006 14:53:58 +0100, Andy Wade
<spambucket@ajwade.clara.co.uk> wrote:

> That Frequency determined by NGET, in its reasonable opinion, as the
> desired operating Frequency of the Total System. This will normally
> be 50.00Hz plus or minus 0.05Hz, except in exceptional circumstances
> as determined by NGET, in its reasonable opinion when this may be
> 49.90 or 50.10Hz. An example of exceptional circumstances may be
> difficulties caused in operating the System during disputes affecting
> fuel supplies.
>
>2. From document BC3, which deals with the frequency control process:
>
> BC3.4.3 Electric Time
> ---------------------
> NGET will endeavour (in so far as it is able) to control electric
> clock time to within plus or minus 10 seconds by specifying changes
> to Target Frequency, by accepting bids and offers in the Balancing
> Mechanism. Errors greater than plus or minus 10 seconds may be
> temporarily accepted at NGET's reasonable discretion.
>
>
>All very well, but ISTM that the biggest problem with using the mains
>alone as a time standard is power cuts, after which you'll always need
>some absolute standard such as MSF, GTS, NTP, etc. to reset your clock.

The traditional approach assuming the outages were brief, was to use a
cheap oscillator (an astable mutivibrator) running from a back up
battery when the mains feed was down.

DG

Andrew Sinclair

2006-04-15, 7:21 pm

In message <e1qv19$gvj$1@inews.gazeta.pl>, n cook <diverse8@gazeta.pl>
writes
>What a swiz, I wanted to see what the real time meter would do at 19.15
>tonight
Wouldn't see any difference. The TARDIS has an internal power supply
and is not reliant on a connection to the National Grid.

Whilst it doesn't cover frequency, this site;

http://www.bmreports.com/bwx_reporting.htm

covers system demand (takes a few seconds usually for the graphs to
load) and other commercial parameters, today capped out at just over 38
GW demand.

Cheers,

Andy
--
Andrew Sinclair http://www.smellycat.org

Christopher Tidy

2006-04-15, 11:21 pm

Andy Wade wrote:
> Christopher Tidy wrote:
>
>
>
> You can download more information than you ever wanted to know about the
> National Grid from here:
>
> http://www.nationalgrid.com/uk/Elec...e/gridcodedocs/
>
> I've pasted two relevant snippets below (NGET stands for National Grid
> Electricity Transmission plc).
>
> 1. From the definitions:
>
> Target Frequency
> ----------------
> That Frequency determined by NGET, in its reasonable opinion, as the
> desired operating Frequency of the Total System. This will normally
> be 50.00Hz plus or minus 0.05Hz, except in exceptional circumstances
> as determined by NGET, in its reasonable opinion when this may be
> 49.90 or 50.10Hz. An example of exceptional circumstances may be
> difficulties caused in operating the System during disputes affecting
> fuel supplies.
>
> 2. From document BC3, which deals with the frequency control process:
>
> BC3.4.3 Electric Time
> ---------------------
> NGET will endeavour (in so far as it is able) to control electric
> clock time to within plus or minus 10 seconds by specifying changes
> to Target Frequency, by accepting bids and offers in the Balancing
> Mechanism. Errors greater than plus or minus 10 seconds may be
> temporarily accepted at NGET's reasonable discretion.
>
>
> All very well, but ISTM that the biggest problem with using the mains
> alone as a time standard is power cuts, after which you'll always need
> some absolute standard such as MSF, GTS, NTP, etc. to reset your clock.

Thanks very much for those useful snippets, Andy. When it refers to a 10
second error in electric time, do you know if it refers to a 10 second
error from the true time at any instant (assuming that the sychronous
clocks were set to the correct time at an instant when the electric time
was correct), or a 10 second cumulative error week on week, month on
month, etc.? It isn't immediately clear to me. You're also right to
point out that you need some kind of absolute time standard if you care
about that sort of accuracy. I don't: all I'm interested in is whether
the grid is accurate enough to make this rather cool clock keep time for
day-to-day purposes, and it seems that the consensus is that it will be
fine.

Best wishes,

Chris

The Natural Philosopher

2006-04-16, 2:21 am

Christopher Tidy wrote:
> Hi all,
>
> I'm thinking of building an electronic clock control circuit which uses
> the 50 Hz mains frequency for time keeping. The reason for this is that
> the clock dial is rather large, so probably wouldn't run for long on
> battery power, and I don't fancy spending £40 buying a programmable
> quartz oscillator chip.
>
> Despite doing some research online and in electrical engineering books,
> I can't find a figure for the accuracy of the time keeping of the UK
> power grid. Perhaps this is because there aren't official bounds set for
> the time error - one of my electrical engineering books says it is a
> legal requirement that the frequency be kept "as close as possible to 50
> Hz" - but even if this is the case it should be possible to determine a
> typical error figure.
>
> From my point of view I'd regard an acceptable error as 5 minutes every
> 6 months. Does anyone know the typical time error seen on the UK grid,
> or where I might find this information? Any suggestions would be much
> appreciated.
>

IIRC it is actually 100% spot on in the long term.

However it tends to go plus minus several seconds during the day as peak
loads tend to slow the generators..they then overrun a bit in the off
peak hours to catch up.

BUT as a matte of standard and poossibly even law, they always do get it
right over the long period.

> Best wishes,
>
> Chris Tidy
>

The Natural Philosopher

2006-04-16, 2:21 am

JANA wrote:
> For any type of accuracy, depending on the power grid is not a dependable
> option! There can be noise, interference, and power dips. On the short
> term, the power grid will be accurate, but over the long term, it can be out
> by a fair amount.

All wrong.

Clocks essentially filter out all the trash, the long term accuracy is
guaranteed by the generating companies, and the one thing that gets you
is really power outages only.

But that was teh one thing you don't mention.

Tony Williams

2006-04-16, 4:21 am

In article <ncb242lsd9g7ee4n76ule9dqiku1tck161@4ax.com>,
Derek ^ <usenet@miniac.demon.co.uk> wrote:

> The traditional approach assuming the outages were brief, was to
> use a cheap oscillator (an astable mutivibrator) running from a
> back up battery when the mains feed was down.

On big tower clocks (which often had difficult access
for adjustment) one standard solution was to make all
power cuts last a multiple of 12 hours exactly, either
manually or with a battery-powered crystal oscillator.

--
Tony XXXXXXXX.

n cook

2006-04-16, 6:21 am

Tony XXXXXXXX <tonyw@ledelec.demon.co.uk> wrote in message
news:4e18540cfatonyw@ledelec.demon.co.uk...
> In article <ncb242lsd9g7ee4n76ule9dqiku1tck161@4ax.com>,
> Derek ^ <usenet@miniac.demon.co.uk> wrote:
>
>
> On big tower clocks (which often had difficult access
> for adjustment) one standard solution was to make all
> power cuts last a multiple of 12 hours exactly, either
> manually or with a battery-powered crystal oscillator.
>
> --
> Tony XXXXXXXX.

Any connection with the tradition/obligation ? that any broken civic clocks
should have their hands set to 12.00 ?

Seriously aside, is there any problem for civic clocks in seriously leaning
towers?
One near me , if picture outside of a file is downloadable here
http://www.nutteing.freeukisp.co.uk/triangle1.jpg
with my assistant holding a plumbob to show the lean
or otherwise part down on
http://www.divdev.fsnet.co.uk/graff.htm

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

Andy Wade

2006-04-16, 8:21 am

Christopher Tidy wrote:

> Thanks very much for those useful snippets, Andy. When it refers to a 10
> second error in electric time, do you know if it refers to a 10 second
> error from the true time at any instant (assuming that the sychronous
> clocks were set to the correct time at an instant when the electric time
> was correct), or a 10 second cumulative error week on week, month on
> month, etc.? It isn't immediately clear to me.

I assumed it means the former, i.e. ±10 s 'absolute' error, but
"electric time" is not defined in the extensive definitions/glossary
section, nor do the strings "electric time" or "electric clock" appear
anywhere else in the complete Grid Code document (546 page PDF!). For
your latter interpretation they'd have to specify the accumulation
period, and I can't see any such specification.

--
Andy

Andy Wade

2006-04-16, 8:21 am

Derek ^ wrote:

> The traditional approach assuming the outages were brief, was to use a
> cheap oscillator (an astable mutivibrator) running from a back up
> battery when the mains feed was down.

Yes, that's why I was careful to say "the biggest problem with using the
mains alone ..."

Cheap clock radios are the only things I've seen that have used crude RC
oscillators to cover mains outages, and their timekeeping is utter crap
- 5 min error in half an hour!

--
Andy

Andrew Gabriel

2006-04-16, 8:21 am

In article <44421feb$0$5002$db0fefd9@news.zen.co.uk>,
Andy Wade <spambucket@ajwade.clara.co.uk> writes:
> Cheap clock radios are the only things I've seen that have used crude RC
> oscillators to cover mains outages, and their timekeeping is utter crap
> - 5 min error in half an hour!

The old brass timeswitches which used to be used on streetlamps
(complete with auto seasonal adjustment) used to continue on clockwork
for several hours during a power cut. On power restore, the synchronous
motor also rewound the clockwork spring. Damn impressive pieces of
mechanical engineering those things were.

There's one road near me which obviously still has timeswitches on the
lamps, but no evidence of the clockwork standby operation, judging by
how all the lights can occasionally go out of sync for a month or so
before someone corrects them.

--
Andrew Gabriel

Derek ^

2006-04-16, 9:21 am

On Sun, 16 Apr 2006 11:45:56 +0100, Andy Wade
<spambucket@ajwade.clara.co.uk> wrote:

>Derek ^ wrote:
>
>
>Yes, that's why I was careful to say "the biggest problem with using the
>mains alone ..."
>
>Cheap clock radios are the only things I've seen that have used crude RC
>oscillators to cover mains outages, and their timekeeping is utter crap
>- 5 min error in half an hour!

Presumably the back up oscillator wasn't adjusted accurately if at all
during manufacture, not surprisingly. people were used to having to
set the clock.

In the '60's most audio equipment, cheap record players etc around
here (Leeds) used to emit a series of peeps at about 6-00 pm, as
schoolkids we believed it was to reset the timeswitches governing the
streetlights once per day. WCHBW

DG

Michael A. Terrell

2006-04-16, 6:21 pm

Andy Wade wrote:
>
> Derek ^ wrote:
>
>
> Yes, that's why I was careful to say "the biggest problem with using the
> mains alone ..."
>
> Cheap clock radios are the only things I've seen that have used crude RC
> oscillators to cover mains outages, and their timekeeping is utter crap
> - 5 min error in half an hour!
>
> --
> Andy

Of course they run fast. That way the alarm will wake you early
enough to reset the clock before you leave for work.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Christopher Tidy

2006-04-16, 7:21 pm

Andy Wade wrote:
> Christopher Tidy wrote:
>
>
>
> I assumed it means the former, i.e. ±10 s 'absolute' error, but
> "electric time" is not defined in the extensive definitions/glossary
> section, nor do the strings "electric time" or "electric clock" appear
> anywhere else in the complete Grid Code document (546 page PDF!). For
> your latter interpretation they'd have to specify the accumulation
> period, and I can't see any such specification.

Thanks for the clarification. Thanks also to everyone else for their
help and suggestions.

Best wishes,

Chris

Don Kelly

2006-04-17, 1:21 am

----------------------------
"Andy Dingley" <dingbat@codesmiths.com> wrote in message
news:rkrv32h5584e3vnuvsq13r5foenjptqgkr@4ax.com...
> On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
> <b.sharrock@ntlworld.com> wrote:
>
>
> Although a squirrel cage uses a synchronous stator winding, it isn't a
> synchronous motor, at least not to this level of timekeeping. Their
> rotors are powered by an induced current in the rotor (the squirrel cage
> itself), not any sliprings or brushgear. This current is only induced if
> the rotor experiences a moving or changing magnetic field - i.e. it
> rotates at a different speed to the field in the stator. They can't
> generate a torque unless there is some "slip", the speed difference
> between synchronous speed and actual rotation. It's notable that the
> more the slip, the more the output torque - so these motors can deliver
> substantial power under load.
>
> A frictionless, resistanceless, hysteresisless squirrel cage motor doing
> no work would accelerate up to synchronous speed and then hold that
> speed spinning freely, doing no work and producing no torque. An
> idealised but possible motor might always run at a known slip which
> could be compensated for by gearing. In practice such effects as
> temperature and lubricant viscosity make this unpredictable, at least
> for clockmaking accuracy.
>
> Clocks use shaded pole motors, which are synchronous. As these don't
> have the same increased torque response to slip they're inherently low
> torque and thus only useful for clocks or other light tasks.
-------------------
Shaded pole motors may be induction or may be synchronous. The shaded pole
just establishes a rotating field in the right direction to get starting
torque.
The difference is in the rotor- either conventional induction motor rotor-
ie. slip needed for torque: or hysteresis synchronous where the
hysteresis-synchronous motor has a core made from two different steels,
giving it a nearly constant accelerating torque up to synchronous speed (as
an induction motor), at which point it locks into synchronism. Certainly
there were some US models (my parents has one and you still see them in
antique stores) which needed a mechanical kick for starting-twist a knob to
spin the gears) but this may have been to having a single winding and not a
shaded pole construction. The rotor doesn't have permanent magnets but
generally has permanent magnet material forming poles and the rest filled in
with a soft iron. Just as with large synchronous motors, the starting is as
an induction motor but running is synchronous.
More expensive than the shaded pole induction motor as used for many small
fans.

Were the Sangamo designs "reluctance" motors- with salient poles and an
induction winding?

--

Don Kelly @shawcross.ca
remove the X to answer

nobody@devnull.spamcop.net

2006-04-17, 3:21 am

Michael A. Terrell wrote:

>If all those areas are connected to a single power grid they still
>have to stay in sync, even if the control system is broken into
>regional centers.

High voltage DC (HVDC) is used to transmit large amounts of power over
long distances or for interconnections between asynchronous grids When
electrical energy is required to be transmitted over very long distances,
it can be more economical to transmit using direct current (An electric
current that flows in one direction steadily) instead of alternating
current (An electric current that reverses direction sinusoidally).
For a long transmission line, the value of the smaller losses, and
reduced construction cost of a DC line, can offset the additional
cost of converter stations at each end of the line. Also, at high AC
voltages significant amounts of energy are lost due to corona discharge
(An electrical discharge accompanied by ionization of surrounding
atmosphere) the capacitance (An electrical phenomenon whereby an
electric charge is stored) between phases or, in the case of buried
cables, between phases and the soil (The part of the earth's surface
consisting of humus and disintegrated rock) or water (Binary compound
that occurs at room temperature as a clear colorless odorless tasteless
liquid; freezes into ice below 0 degrees centigrade and boils above
100 degrees centigrade; widely used as a solvent) in which the cable
s buried. Since the power flow through an HVDC link is directly
controllable, HVDC links are sometimes used within a grid to stabilize
the grid against control problems with the AC energy flow.

Also see
http://www.absoluteastronomy.com/re..._direct_current
http://en.wikipedia.org/wiki/HVDC
http://www.aip.org/tip/INPHFA/vol-9/iss-5/p8.html

Michael A. Terrell

2006-04-17, 1:21 pm

nobody@devnull.spamcop.net wrote:
>
> High voltage DC (HVDC) is used to transmit large amounts of power over
> long distances or for interconnections between asynchronous grids When
> electrical energy is required to be transmitted over very long distances,
> it can be more economical to transmit using direct current (An electric
> current that flows in one direction steadily) instead of alternating
> current (An electric current that reverses direction sinusoidally).
> For a long transmission line, the value of the smaller losses, and
> reduced construction cost of a DC line, can offset the additional
> cost of converter stations at each end of the line. Also, at high AC
> voltages significant amounts of energy are lost due to corona discharge
> (An electrical discharge accompanied by ionization of surrounding
> atmosphere) the capacitance (An electrical phenomenon whereby an
> electric charge is stored) between phases or, in the case of buried
> cables, between phases and the soil (The part of the earth's surface
> consisting of humus and disintegrated rock) or water (Binary compound
> that occurs at room temperature as a clear colorless odorless tasteless
> liquid; freezes into ice below 0 degrees centigrade and boils above
> 100 degrees centigrade; widely used as a solvent) in which the cable
> s buried. Since the power flow through an HVDC link is directly
> controllable, HVDC links are sometimes used within a grid to stabilize
> the grid against control problems with the AC energy flow.
>
> Also see
> http://www.absoluteastronomy.com/re..._direct_current