"Christopher Tidy" wrote in message
...
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?

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.

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

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

On 14 Apr 2006 21:53:18 GMT, (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.e...1a4f753?hl=en&

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

http://groups.google.com/group/uk.rec.subterranea/msg/dd48c794775000bf

--
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

"daestrom" wrote in message
...


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...

In article
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.

I have a vintage synchronous clock which seems to keep good time over a
period of months.

In message , n cook
writes
Some future use for the dips in mains frequency use to reduce National Grid
load
http://www.publications.parliament.u...n/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

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 he

http://www.nationalgrid.com/uk/Elect.../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

Andrew Sinclair wrote in message
...
In message , n cook
writes
Some future use for the dips in mains frequency use to reduce National
Grid
load

http://www.publications.parliament.u...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


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/

On Sat, 15 Apr 2006 14:53:58 +0100, Andy Wade
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

In message , n cook
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

Andy Wade wrote:
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 he

http://www.nationalgrid.com/uk/Elect.../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

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

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.

In article ,
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.

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 Williams.

Tony Williams wrote in message
...
In article ,
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.

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 Williams.

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/

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

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

In article ,
Andy Wade 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

On Sun, 16 Apr 2006 11:45:56 +0100, Andy Wade
wrote:

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!

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

Andy Wade wrote:

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


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

Andy Wade wrote:
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.

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

Best wishes,

Chris

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/ref...direct_current
http://en.wikipedia.org/wiki/HVDC
http://www.aip.org/tip/INPHFA/vol-9/iss-5/p8.html

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/ref...direct_current
http://en.wikipedia.org/wiki/HVDC
http://www.aip.org/tip/INPHFA/vol-9/iss-5/p8.html


I'm quite familiar with HVDC distribution systems, but more
generators are connected via AC than DC and those DO have to be in phase
and have the frequency controlled to keep the rest of the grid happy.

BTW: HVDC distribution has been discussed to death on both the
news:sci.electronics.design and news:alt.electrical.engineering
newsgroups.

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

"Michael A. Terrell" wrote in
:

snip


I'm quite familiar with HVDC distribution systems, but more
generators are connected via AC than DC and those DO have to be in
phase and have the frequency controlled to keep the rest of the grid
happy.

BTW: HVDC distribution has been discussed to death on both the
news:sci.electronics.design and news:alt.electrical.engineering
newsgroups.


Mention of HVDC reminds me that the Channel link is one such (at least,
I think that's what I remember). So that prompts me to ask, how closely
synchronised are the UK and France, and indeed the other European countries
with each other?

(Hope I haven't missed this question somewhere else in this huge
thread!)

--
Rod

In article ,
Rod writes:

Mention of HVDC reminds me that the Channel link is one such (at least,
I think that's what I remember). So that prompts me to ask, how closely
synchronised are the UK and France, and indeed the other European countries
with each other?

(Hope I haven't missed this question somewhere else in this huge
thread!)

I haven't seen a synchronisation map since the Berlin wall came down.
However, before that, most of Western Continental Europe was a single
zone controlled from Switzerland, Eastern Europe was controlled from
Moscow (can't recall if it was a single zone) and Great Britain was
its own synchronisation zone controlled from Reading, Berkshire.

When the Berlin wall came down, West Berlin was very short of power
and had been suffering power cuts as a result. East Berlin had a
surpless but it was produced by horribly poluting power stations.
They couldn't be easily linked as they were in different synchronisation
zones. Also, whilst West Berlin was 50Hz +- 0.5Hz, East Berlin's
frequency varied by considerably more than that. I don't know how this
was eventually resolved -- I read about it only a few months after the
wall came down and there was no resolution at that time. Lots of UK
power (and gas) engineers got contracted out to the former East Germany
just after unification as part of a massive repair of their broken
infrastructure (loads of leaking gas mains was a serious problem).

--
Andrew Gabriel

In message
Rod wrote:

... Mention of HVDC reminds me that the Channel link is one such (at
least, I think that's what I remember). So that prompts me to ask, how
closely synchronised are the UK and France, and indeed the other
European countries with each other?

UK-France, like all lengthy underwater/undergound (i.e. high
capacitance) links, is DC, so obviating any need for synchronism.

Don't know about the rest of Europe, but inter-system links elsewhere,
even when 'overhead', are often DC primarily to avoid the need for sync.

--
Peter Duck

----------------------------
wrote in message
...



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/ref...direct_current
http://en.wikipedia.org/wiki/HVDC
http://www.aip.org/tip/INPHFA/vol-9/iss-5/p8.html

So?
Note that Michael said "single" power grid.

You are considering a point to point asynchronous connection between two
systems. A DC link is often used for this purpose even in some cases where
the converter stations are back to back but an asynchronous tie is required
because of differing frequencies (Japan)or simply because otherwise there
are problems maintaining a synchronous tie between two large systems
(Alberta and points west and south-Saskatchewan and points east and south).

It is true that they can be at different frequencies but...

within each system, machines have to be in synchronism. In the case of the
NW power pool, a DC backbone is used, as you suggest indirectly, in order to
maintain stability of the system which implies that it is used to maintain
synchronism in a system which might have problems otherwise.


--

Don Kelly @shawcross.ca
remove the X to answer

(Andrew Gabriel) wrote in
:

snip

I haven't seen a synchronisation map since the Berlin wall came down.

Haven't been back to Berlin since the wall was put up! (I was there when it
was built.)


I don't
know how this was eventually resolved -- I read about it only a few
months after the wall came down and there was no resolution at that
time.

Thanks for the replies.

--
Rod

"Michael A. Terrell" wrote in message
...


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/ref...direct_current
http://en.wikipedia.org/wiki/HVDC
http://www.aip.org/tip/INPHFA/vol-9/iss-5/p8.html


I'm quite familiar with HVDC distribution systems, but more
generators are connected via AC than DC and those DO have to be in phase
and have the frequency controlled to keep the rest of the grid happy.


You seem to be laboring under the idea that all the AC generators tied to
the grid have to be carefully regulated to stay in sync with each other
through some incredibly precise timing.

That isn't the case. A generator is brought on-line by carefully regulating
the speed and getting it in phase. That is a bit tricky. But once tied to
the grid, 'keeping in sync' is done by the load current and physics. In
fact, base load units don't even have frequency control once on-line. The
speed set-point for the governor is run several hz up out of the way and the
turbine controls are controlled by a 'load' setting. The operator dials in
the amount of MW load they are supposed to carry, and the controls monitor
MW and steam flow. They don't respond at all to frequency changes unless
the frequency rises to the point the unit is in danger of over-speeding.

During grid disturbances, base load units will naturally speed up/slow-down
as grid frequency changes, maintaining their load output based on
'load-set'. Only 'regulating duty' plants monitor generator speed/freq and
make any sort of adjustment based on changes in speed/freq. And
'regulating' units make up a fairly small fraction of all AC units.

The vast majority of AC generators will 'stay in sync' just by virtue of the
physics of synchronous machines. Only if under-excited, or significant
reactance in their output line are they likely to 'pull out' of sync with
the grid. (and that's a *bad thing*)

daestrom

"Peter Duck" wrote in message
...
In message
Rod wrote:

... Mention of HVDC reminds me that the Channel link is one such (at
least, I think that's what I remember). So that prompts me to ask, how
closely synchronised are the UK and France, and indeed the other
European countries with each other?

UK-France, like all lengthy underwater/undergound (i.e. high
capacitance) links, is DC, so obviating any need for synchronism.

Don't know about the rest of Europe, but inter-system links elsewhere,
even when 'overhead', are often DC primarily to avoid the need for sync.


Indeed. There were a few 'experiments' to get the eastern and western US
grids in sync a couple of times in the '70's or '80's. Could get them
there, but the few tie-lines they were using couldn't carry enough power to
keep them in sync. As soon as one side of the country started to
slow/speedup, the amount of load that would start flowing required the line
to trip open. Then slowly work them back in sync again, and try it again.
Gave up after a while. Not much use in it.

But the US does have several HVDC links between grid segments. This allows
power transfer without synching. (and better control of the power flow)

daestrom

daestrom wrote:

You seem to be laboring under the idea that all the AC generators tied to
the grid have to be carefully regulated to stay in sync with each other
through some incredibly precise timing.


I never said that at all, but I did say that the sped and phase have
to match to connect a new generator to a grid.


That isn't the case. A generator is brought on-line by carefully regulating
the speed and getting it in phase. That is a bit tricky. But once tied to
the grid, 'keeping in sync' is done by the load current and physics. In
fact, base load units don't even have frequency control once on-line. The
speed set-point for the governor is run several hz up out of the way and the
turbine controls are controlled by a 'load' setting. The operator dials in
the amount of MW load they are supposed to carry, and the controls monitor
MW and steam flow. They don't respond at all to frequency changes unless
the frequency rises to the point the unit is in danger of over-speeding.


If you would have read the entire thread, I described how the
generators are synched, and that the grid keeps them in sync unless
something goes wrong. I also stated that the generator was fed more
fuel or water to actually produce power for the grid rather than just
coasting along, in phase, one it was connected to the grid. I studied
the subject with college textbooks on power generation and distribution
when I was 13.


During grid disturbances, base load units will naturally speed up/slow-down
as grid frequency changes, maintaining their load output based on
'load-set'. Only 'regulating duty' plants monitor generator speed/freq and
make any sort of adjustment based on changes in speed/freq. And
'regulating' units make up a fairly small fraction of all AC units.

The vast majority of AC generators will 'stay in sync' just by virtue of the
physics of synchronous machines. Only if under-excited, or significant
reactance in their output line are they likely to 'pull out' of sync with
the grid. (and that's a *bad thing*)


Of course the larger the spinning mass in the generator, the more the
inertia, and the less likely to be kicked out of phase. The
experimental nuclear power plant at Ft. Greely, Alaska was steam driven
and unable to adapt to rapid load changes so they blew out quite a few
bearings in the turbines before they finally gave up and shut it down.
They would barely get it running an synchronized to the Alaskan power
grid when someone would fire up another generator and switch it on line
without contacting other providers on the grid. The system was
unstable, in frequency, voltage and a lot of outages. I watched my 120
VAC feed climb to over 190 volts one day, as circuit breakers all over
the complex were tripping out. It took me a couple hours to get all the
studio equipment and transmitters back in service that day. It was one
of the few times that I was happy that the towers were too short to need
lights.


daestrom

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

Yes, this must be the case. From memory, the national grid a long time
ago (maybe 30 years or more) was not regulated to ensure long term mean
frequency accuracy (ie. the average could drift slowly) and the was
noticeable on mains synchronised clocks. Some time after this things
changed so that the long term accuracy was controlled.

"Michael A. Terrell" wrote in message
...


daestrom wrote:

You seem to be laboring under the idea that all the AC generators tied to
the grid have to be carefully regulated to stay in sync with each other
through some incredibly precise timing.


I never said that at all, but I did say that the sped and phase have
to match to connect a new generator to a grid.


That isn't the case. A generator is brought on-line by carefully
regulating
the speed and getting it in phase. That is a bit tricky. But once tied
to
the grid, 'keeping in sync' is done by the load current and physics. In
fact, base load units don't even have frequency control once on-line.
The
speed set-point for the governor is run several hz up out of the way and
the
turbine controls are controlled by a 'load' setting. The operator dials
in
the amount of MW load they are supposed to carry, and the controls
monitor
MW and steam flow. They don't respond at all to frequency changes unless
the frequency rises to the point the unit is in danger of over-speeding.


If you would have read the entire thread, I described how the
generators are synched, and that the grid keeps them in sync unless
something goes wrong. I also stated that the generator was fed more
fuel or water to actually produce power for the grid rather than just
coasting along, in phase, one it was connected to the grid. I studied
the subject with college textbooks on power generation and distribution
when I was 13.
---------------



During grid disturbances, base load units will naturally speed
up/slow-down
as grid frequency changes, maintaining their load output based on
'load-set'. Only 'regulating duty' plants monitor generator speed/freq
and
make any sort of adjustment based on changes in speed/freq. And
'regulating' units make up a fairly small fraction of all AC units.

The vast majority of AC generators will 'stay in sync' just by virtue of
the
physics of synchronous machines. Only if under-excited, or significant
reactance in their output line are they likely to 'pull out' of sync with
the grid. (and that's a *bad thing*)


Of course the larger the spinning mass in the generator, the more the
inertia, and the less likely to be kicked out of phase. The
experimental nuclear power plant at Ft. Greely, Alaska was steam driven
and unable to adapt to rapid load changes so they blew out quite a few
bearings in the turbines before they finally gave up and shut it down.
---------

The problem is not the steam turbine/governor which responds relatively
quickly (much faster than a hydro machine), but likely in the reactor
dynamics and control. It appears that the machine was kicked off the system
and an uncontrolled shutdown occurred. Wiping of bearings can occur in
uncontrolled, coast slowly to a stop, shutdowns. It happened to "Big Ally"
in NYC in the '65 blackout.

Most college texts - at least in the past, when you were 13, didn't really
discuss synchronisation except for the general concept, nor the problem of
load sharing and the effects of governor "droop".

It is true that a heavier machine will respond more slowly for a given
accelerating power but this is a mixed blessing as it takes longer to bring
it under control and time is of the essence in considering system stability.
A smaller machine is more likely to swing rapidly but is normally easier
for the system to rein in (system impedances will affect this). I assume
that the experimental machine was fairly small as well as being weakly tied
to the system but there could well be other, control, problems with the
governor system and load sharing coordination.
--

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

Don Kelly wrote:

The problem is not the steam turbine/governor which responds relatively
quickly (much faster than a hydro machine), but likely in the reactor
dynamics and control. It appears that the machine was kicked off the system
and an uncontrolled shutdown occurred. Wiping of bearings can occur in
uncontrolled, coast slowly to a stop, shutdowns. It happened to "Big Ally"
in NYC in the '65 blackout.

Most college texts - at least in the past, when you were 13, didn't really
discuss synchronisation except for the general concept, nor the problem of
load sharing and the effects of governor "droop".

It is true that a heavier machine will respond more slowly for a given
accelerating power but this is a mixed blessing as it takes longer to bring
it under control and time is of the essence in considering system stability.
A smaller machine is more likely to swing rapidly but is normally easier
for the system to rein in (system impedances will affect this). I assume
that the experimental machine was fairly small as well as being weakly tied
to the system but there could well be other, control, problems with the
governor system and load sharing coordination.


It was a small, poorly designed grid in subzero weather. The plant
was built as a feasibility study to see how well a reactor would work in
that climate. It had been decommissioned just before I arrived, but I
knew the EEs and MEs who maintained it, since most of them had been
borrowed from the diesel powered plant that the reactor was supposed to
replace. The brick building was still there, right across the street
from my barracks.


As far as the textbooks they were published in '60 and '61, so I am
sure that there are a lot better text available 45 years later. Like
you said, they did cover the basics of how a power grid works, and how
they were synchronized. I think they were first and second year texts,
but they are long gone. I went into
high power RF and microwave communications instead of power generation
and distribution, but I still remember the basics.

--
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

"Michael A. Terrell" wrote in message
...


daestrom wrote:

You seem to be laboring under the idea that all the AC generators tied to
the grid have to be carefully regulated to stay in sync with each other
through some incredibly precise timing.


I never said that at all, but I did say that the sped and phase have
to match to connect a new generator to a grid.


That isn't the case. A generator is brought on-line by carefully
regulating
the speed and getting it in phase. That is a bit tricky. But once tied
to
the grid, 'keeping in sync' is done by the load current and physics. In
fact, base load units don't even have frequency control once on-line.
The
speed set-point for the governor is run several hz up out of the way and
the
turbine controls are controlled by a 'load' setting. The operator dials
in
the amount of MW load they are supposed to carry, and the controls
monitor
MW and steam flow. They don't respond at all to frequency changes unless
the frequency rises to the point the unit is in danger of over-speeding.


If you would have read the entire thread, I described how the
generators are synched, and that the grid keeps them in sync unless
something goes wrong. I also stated that the generator was fed more
fuel or water to actually produce power for the grid rather than just
coasting along, in phase, one it was connected to the grid. I studied
the subject with college textbooks on power generation and distribution
when I was 13.


Then why do you keep repeating....

"generators are connected via AC than DC and those DO have to be in phase
and have the frequency controlled to keep the rest of the grid happy."

And similar phrases about AC generators needing extremely accurate frequency
control. As I pointed out, most generators on the grid are *not* frequency
regulating. Once tied in, they just follow the grid frequency. Base load
units are a prime example of this. The governors are run up out of the way
so they are not controlling the turbine at all once connected.

snip

Of course the larger the spinning mass in the generator, the more the
inertia, and the less likely to be kicked out of phase. The
experimental nuclear power plant at Ft. Greely, Alaska was steam driven
and unable to adapt to rapid load changes so they blew out quite a few
bearings in the turbines before they finally gave up and shut it down.
They would barely get it running an synchronized to the Alaskan power
grid when someone would fire up another generator and switch it on line
without contacting other providers on the grid. The system was
unstable, in frequency, voltage and a lot of outages. I watched my 120
VAC feed climb to over 190 volts one day, as circuit breakers all over
the complex were tripping out. It took me a couple hours to get all the
studio equipment and transmitters back in service that day. It was one
of the few times that I was happy that the towers were too short to need
lights.


Not familiary with Ft Greely, but I would guess that such a system was not
really part of a large grid. Sounds more like a small number of units with
a relatively small amount of load ( 500 MW???). Yes, controlling such a
setup does require more coordination. Especially since one unit can make a
rapid change to the system's frequency.

daestrom