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'[OT] Re: Long, accurate times...'
1999\06\08@214512 by Tony Nixon

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Lynx {Glenn Jones} wrote:
>
> Why is this done? I mean why does the power line need to be EXACTLY 60Hz?

To the best of my knowledge, everything that runs off the grid is
'tuned' to 60Hz to get the best power transfer across the system.
Transformers, motors etc. If this frequency was to alter, a lot of
eqipment would complain. Even the weights clamped onto the overhead
wires near the insulators are tuned to dampen oscillations at this
frequency.

The power companies may complain too because the power meters would give
incorrect readings.

--
Best regards

Tony

'The Engine' - Design your own programmer.

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1999\06\08@215539 by Reginald Neale

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>Lynx {Glenn Jones} wrote:
>>
>> Why is this done? I mean why does the power line need to be EXACTLY 60Hz?
>
>To the best of my knowledge, everything that runs off the grid is
>'tuned' to 60Hz to get the best power transfer across the system.
>Transformers, motors etc. If this frequency was to alter, a lot of
>eqipment would complain. Even the weights clamped onto the overhead
>wires near the insulators are tuned to dampen oscillations at this
>frequency.
>
>The power companies may complain too because the power meters would give
>incorrect readings.
>
 But mostly, I think, it needs to be exactly SOMETHING so that the
 power companies can trade energy back and forth across the power
 grid. Imagine connecting two lines when one is at positive peak
 and the other is at negative peak. KABLOOEY!

 Reg Neale

1999\06\08@232227 by Matthew Ballinger

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In a message dated 6/8/99 9:56:09 PM Eastern Daylight Time,
.....nealeKILLspamspam@spam@SERVTECH.COM writes:

> >> Why is this done? I mean why does the power line need to be EXACTLY 60Hz?
>  >
>  >To the best of my knowledge, everything that runs off the grid is
>  >'tuned' to 60Hz to get the best power transfer across the system.
>  >Transformers, motors etc. If this frequency was to alter, a lot of
>  >eqipment would complain. Even the weights clamped onto the overhead
>  >wires near the insulators are tuned to dampen oscillations at this
>  >frequency.
>  >
>  >The power companies may complain too because the power meters would give
>  >incorrect readings.
>  >
>    But mostly, I think, it needs to be exactly SOMETHING so that the
>    power companies can trade energy back and forth across the power
>    grid. Imagine connecting two lines when one is at positive peak
>    and the other is at negative peak. KABLOOEY!
>
>
       Not really. Only real load would be affected by frequency mismatches.
Reactive load would not be affected at all. Frequency of the generator would
*have* to be same as grid frequency weather it wants to or not (or it becomes
a motor). If you set no load frequency of its frequency regulator (turbine
speed) at grid frequency it picks up no Real load ( only reactive, depending
on voltage regulator setting). Its no load freqency setting must actually
slighty higher than grid frequency. The Reactive load is transferred by the
generator's voltage regulator setting. This is probably a bit confusing,
sorry. Matt.

1999\06\08@232650 by Dave VanHorn

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> > >> Why is this done? I mean why does the power line need to be EXACTLY
60Hz?


So people's clocks read right.
(There was a warning system for nuclear attack that worked when the US power
grid switched to 50 Hz.)

1999\06\08@235045 by Sean Breheny

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Actually, though, I have seen graphical representations of the phase over
large power grids and it DOES vary, quite a bit. In fact, you can tell
which way power is traveling down a power transmission line by looking at
which end of it leads in phase. Power distribution people use this info to
determine power flow around a large grid AND to see when the grid might
break down (TOO large a phase gradient, in many cases).

Sean

At 09:55 PM 6/8/99 -0400, you wrote:
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1999\06\09@002411 by Chris Eddy

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I visited the local power company in western Pennsylvania one afternoon
(fellow engineers that I know showed me around).  While at the control room, I
asked them why the frequency reading on a display was not exactly 60 Hz.
They said that it rarely is, and that they run above or below 60 for some
period of time to 'catch' back up to where they ought to be.  It sounded like
a portion of the explanation was hooey, but then, if a zero crossing circuit
wants to track total time, and it fell behind, it would have to catch up.
(yea, far fetched).  That was the best explanation I could get.  The moral of
the story is that one should not count on the power company for any accuracy
at all.

Chris Eddy

Sean Breheny wrote:

{Quote hidden}

1999\06\09@004731 by Sam Laur

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> So people's clocks read right.
> (There was a warning system for nuclear attack that worked when the US power
> grid switched to 50 Hz.)

Maybe it's just in case European terrorists strike and want to make US power
the same as in Europe? Imagine all those devices popping when they get a
taste of 230V, 50 Hz... better than any EMP :) (of course it doesn't kill
battery powered devices, but so what.)

Anyway, on the topic of the subject (but still off-topic of the list) :
At least here in Finland we have yet another stable time/frequency source;
the national broadcasting company (Yleisradio) apparently bases the line
frequency (15625 Hz) on a very accurate oscillator (Rubidium). So there's
a transmitter with lots of output power, easy to make an antenna for, etc.

1999\06\09@013933 by Nick Taylor

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Chris Eddy wrote:
>
> I visited the local power company in western Pennsylvania one afternoon
> (fellow engineers that I know showed me around).  While at the control room, I
> asked them why the frequency reading on a display was not exactly 60 Hz.
> They said that it rarely is, and that they run above or below 60 for some
> period of time to 'catch' back up to where they ought to be.  It sounded like
> a portion of the explanation was hooey, but then, if a zero crossing circuit
> wants to track total time, and it fell behind, it would have to catch up.
> (yea, far fetched).  That was the best explanation I could get.  The moral of
> the story is that one should not count on the power company for any accuracy
> at all.

The power line frequency may never be stable at an exact 60 cps, but
I'll bet a nickel that over a period of time it averages 86,400 cycles
per day.

- - - Nick - - -

1999\06\09@072605 by Nigel Orr

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At 22:23 08/06/99 -0500, you wrote:
>(There was a warning system for nuclear attack that worked when the US power
>grid switched to 50 Hz.)

Sounds fascinating- care to elaborate?  Did the entire grid have to drop to
50Hz for the alarm to sound?  Or was that the alarm?

Nigel (in 50Hz-land)...

1999\06\09@130530 by William K. Borsum

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At 11:42 AM 6/9/99 +1000, you wrote:
>Lynx {Glenn Jones} wrote:
>>
>> Why is this done? I mean why does the power line need to be EXACTLY 60Hz?

Nuther reason are motors--speed is heavily dependent on frequency.  And
some equipment is heavily dependent on the precision of the speed of the
motor driving it.  Ditto of the design of the motors, internal inductances,
etc.

Historically--why 60 Hz?  I dunno.  Its 50 Hz in most of Europe.  Old
aircraft systems used to run at 400 (transformers could be smaller).
Kelly

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1999\06\10@101214 by J Nagy

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>Chris Eddy et al wrote:
>>
>> I visited the local power company in western Pennsylvania one afternoon
>> (fellow engineers that I know showed me around).  While at the control
>>room, I
>> asked them why the frequency reading on a display was not exactly 60 Hz.
>> They said that it rarely is, and that they run above or below 60 for some
>> period of time to 'catch' back up to where they ought to be.  It sounded
>>like
>> a portion of the explanation was hooey, but then, if a zero crossing circuit
>> wants to track total time, and it fell behind, it would have to catch up.
>> (yea, far fetched).  That was the best explanation I could get.  The
>>moral of
>> the story is that one should not count on the power company for any accuracy
>> at all.
>
>The power line frequency may never be stable at an exact 60 cps, but
>I'll bet a nickel that over a period of time it averages 86,400 cycles
>per day.

       I've been watching this thread for a while and just have to
comment. As well as my PIC business, I have worked for a large electrical
utility here in Canada for the past 20yrs. Most of that time has been
around the protection and control of large equipment, so if the grey cells
are still in tact...

       - The frequency is never exactly 60Hz. I've often seen about 59.98
as the normal daytime frequency. If you think about it, this is due to ever
increasing loads during the daytime (when the peak occurs, except during
important events like Canada-Russia hockey games). Generation is added in
response to increasing loads (and the resulting decrease in frequency). At
night when loads are reduced, frequency rises as the system is
overgenerated for the load.

       - The *long-term* number of cycles per day is maintained at a
constant value traceable to National (atomic clock) standards. No one can
guarantee that the daily number of cycles will be exactly maintained,
though. Think about it. Frequency is controlled by generation, and
generation is in 'quantums' of perhaps 540MW. Don't go building any
circuits that reset after a specific number of cycles that you call 24hrs!

       - One point that many people fail to realize is that generators on
a grid *can not* run at different frequencies. We have a large grid
interconnected here in the NorthEast corner of North America, and all the
generators run at the same frequency. Only relative phase angles are
changed (by adding or reducing steam/water) to effect changes in power flow.

       - To say that the frequency was reduced to 50Hz is absurd. The
large steam machines that generate power usually run at a constant 3600rpm,
and cannot tolerate speeds more than a few percent from it. I believe we're
set to have *all load* tripped off by 58.5 Hz if the frequency were ever to
drop that far. Somebody is joking to say we'd ever have 50Hz in North
America.

       Just my $.03 (with the exchange rate).


       Jim Nagy
       Elm Electronics
 ICs for Experimenters
http://www.elmelectronics.com/

1999\06\10@202033 by Graeme Smith

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Hi....

When the power company connects to the network, it can either "Sell"
power, or "Buy" it depending on the capacity of its generators.

When they say they are "Catching up" in all liklihood, they have been
unable to supply enough electricity to meet the needs of their service
area, so they are "Selling" power to overcome the cost of the power they
bought, when they were undersupplying.

The network keeps a certain reserve amount available at all times, and
power companies attempt to minimize their purchases of power, when the net
allows, so that they can sell the power to their subscribers at a greater
profit margin.

This should have nothing to do with the frequency of the power feeds, but
it might affect the "Power Factor" which is a measure of how well the
inductive and capacitative reactance ballance across the whole network.

If your powerfactor drops below a certain set point, the generator
actually acts as if it were out of phase, and a parasitic frequency is
developed that can cause the power to fluctuate and destroy sensitive
equipment, such as the ballance of a set of gyros...

(used to be a real problem when we were transferring from ship to shore
power.)

Most power stations are much more interested in keeping the power factor
ballanced than in keeping the cycles at 60 hz nominal.

                               GREY

GRAEME SMITH                         email: grysmithspamspam_OUTfreenet.edmonton.ab.ca
YMCA Edmonton

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(I moved across the hall! :) )

Email will remain constant... at least for now.


On Tue, 8 Jun 1999, Chris Eddy wrote:

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