Power Grid Freq Variations To Be Allowed

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daestrom wrote:
[snip]

Frequency isn't regulated on a per-plant basis. The system operator will monitor the grid frequency and lead or lag from an ideal 60 Hz cycle count. They will schedule generation to be added or subtracted based on these figures. Unless your plant is intended to run islanded on occasion, such frequency regulation is unneeded.
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Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
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wrote:

many of those "flashing 12:00" clocks DO need line frequency to count time. Not all of them have xtal or ceramic resonators providing the 1 sec pulses needed for the time count. Otherwise,a simple lithium coin cell or Supercap backup would retain the timekeeping for a long time,and short power interruptions would not send the clock back to flashing 12:00.
Actually,using line freq is usually more accurate than the xtal or ceramic resonator timebases,over a long time frame. Unless an xtal timebase is precisely tuned and temp compensated,they are not accurate over long times.
I used to do such calibrations.
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Jim Yanik
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Jim Yanik wrote:

Nope, that was the very very early days of digital clocks with discrete logic. Any device built in the last few decades that "flashes 12:00" is microprocessor based and will not be using line frequency for reference.

Adding such a backup adds cost to the device, which is why many do not have such backup. Most actual clocks have a backup battery compartment for use with regular batteries.

Sure, but the crystal is accurate enough for consumer use. Many of the consumer devices don't even have AC power available to them to monitor the line frequency of since they use wall wart or line lump DC power supplies.

I've soldered PTC thermister heaters onto crystals to provide temperature stabilization. Most applications, including consumer timing don't need that level of accuracy, particularly given that most such devices have their time reset at least twice a year.
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On 6/26/2011 2:07 PM, Pete C. wrote:

Many digital clocks listen to WWV NIST radio stations to set the time. I bought such a clock years ago and just a few years ago I bought an inexpensive Sony clock radio that had the same feature. I'm not sure if it got its time signal from WWV or there is something now being broadcast by radio stations or if it picks it up from a cellphone tower. There seem to be a lot of things sending out time signals. Heck, if I'm remembering right, POTS line caller ID does it too.
TDD
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On Sun, 26 Jun 2011 18:56:56 -0500, The Daring Dufas
[snip]

I've had clocks that do that, and clocks that PRETEND to do that.

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Mark Lloyd
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On 6/28/2011 4:41 PM, Mark Lloyd wrote:

I had the atomic clock for years which had a WWV radio receiver built in and the newer Sony clock radio set its time in some mysterious way. ^_^
TDD
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On 6/25/2011 12:54 PM, Pete C. wrote:

Often they are simply counting zero crossings as a timebase so if the line frequency drifts the device does too.

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George wrote:

Only if the device in question is about 30+ years old and using discrete logic. Anything "flashing 12:00" built in the last few decades is microprocessor controlled and using a crystal timebase.
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Pete C. wrote:

Dad built one of these kits in the early 1970s:
http://www.hydroponicsonline.com/store/img-hydroponics/heathkit-gc-1005-digital-electronic-clock-w-manual_320669615117.jpg
Power outage causes it to display 88:88:88, and it's line locked, no crystal. He said it started to be off by a few seconds a month, starting a couple of years ago, and he suspects the power company.
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On Sun, 26 Jun 2011 15:13:34 -0700 (PDT), "larry moe 'n curly"

I knew several *engineers* who had the government buy these things for them under the GI bill. They were "studying to become TV repairmen". Right.

Displaying 88:88:88 makes more sense than 12:00:00. Some will then start incrementing - *bad* design.
The power company is likely more accurate than a crystal. The cumulative error over a long period (month) should be zero. The error could also be the zero-crossing detector getting noisy. Often it'll get much worse.
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snipped-for-privacy@att.bizzzzzzzzzzzz wrote:

I think a lot of them did it only to get free equipment or maybe a monthly stipend. Actually I don't know if the GI Bill paid stipends for courses by mail. One of my father's buddies mentioned ending up with a bunch of Heathkits, including a big TV (big for the time), but another friend went with a differnet company that furnished a line of kits that weren't nearly as good. (something about the TV failing every month, just after becoming very bright and smelling like tar). My father didn't major in electronics or engineering but did manage to design and build a digital clock from TTL chips. He hated its LED display so much that he bought a second Heathkit clock.
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On Thu, 30 Jun 2011 23:41:02 -0700 (PDT), "larry moe 'n curly"

Yep. That's why I said "Right.". They were IBM design engineers, not likely to take up TV repair for a career but the "free" TV was worth their time. They would sit around the office and "dry lab" the tests needed to get the next part. There were a dozen of so of them, including my manager.

I think they did originally, then dropped that. Or it may have been means tested.

I never liked digital clocks so never bothered making one.
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On Sat, 25 Jun 2011 09:04:48 -0400, "Ed Pawlowski"
[snip]

A digital clock is a counter. A plug-in clock counts the cycles of the AC coming in. A battery clock uses a crystal oscillator.
A plug in clock with battery backup probably does NOT have a crystal, but a cheap RC circuit. That's not very precise. Most seem to be fast during power failures. If power fails from 6:00 to 7:00, the clock may show 7:34.

BTW, I once worked on a fancy clock that runs a chart recorder. It used a PLL to convert the 60Hz to something higher (6.4KHZ IIRC), which would then be divided down to 64Hz to drive a stepper motor. This extra complexity had to do with being able to get the exact same speeds while using 50Hz. b
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On 6/26/2011 1:56 PM, Mark Lloyd wrote:

Four devices with digital clocks in my house regularly gain 10-20 seconds/week, even when there are no power outages: (1)2 year old DVR (non-TIVO) connected to an antenna for input (no cable/satellite/FIOS) that has only a 30 second memory in case of power failure (probably a small capacitor), 3 year old microwave oven, (3) 10 year old clock-radio, and (4) 15 year old VCR with a 1 hr. memory in case of power failure. All 4 are on different circuit breakers. I've had our power company check our line for noise, voltage, and/or frequency abnormalities and they found none. 3 other digital clock radios, varying in age from 1-15 years old, some on the same and some on different house circuits keep essentially perfect time. I use timer recording on the VCR and DVR regularly and if I don't reset their clocks weekly, I can lose the end of programs I record unless I always add time at the end. No one has ever proposed an explanation or a serious fix for this situation.
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[snip]

Maybe you could leave one of those devices at a friend's house in another city and see if it runs fast there too.
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Mark Lloyd
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On 6/28/2011 5:45 PM, Mark Lloyd wrote:

Thanks for the suggestion Lloyd. However, with 4 digital clocks behaving this way, I find it hard to believe that the clocks are at fault. I suspect the power line is despite the power company's failure to find problems here. Given that my power is provided by the infamous PEPCO, I don't exactly have faith in their reassurances. This is the same power company that caused me to waste $150 when I called them to report an open neutral in their supply and they told me to hire an electrician because they insisted that problem must be in my house. (The electrician confirmed my diagnosis and when PEPCO repaired the supply line, there wasn't a word of apology - or a refund/rebate of my electrician's bill.)
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So what. Cumulative phase error on rhe grid was allowed to grow pretty large. I think I remember a minute error or more. The total cycle count, however was always corrected, often late at night.
Applications that required accurate frequency provided their own standards. It was a big business for HP and others. Television used a field rate of 60/sex. My entire remembrance of commercial TV has been standards that provided their own synchroinzation that did not require accurate timing from the grid.
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Sam

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To change the frequency they have to brake or accelerate the generator. What I can't understand is which station is in charge of monitoring the frequency and issuing commands to other power stations to speed up or slow down?
Frequency variation is not a big deal. When you have a power outage, the voltage and hence frequency go to zero in a haphazard way. So if line frequency variation would cause chaos, power outage should cause many times the chaos.
But we have been living with the ocassional power outage, I think the minute line frequency variation is not going to do any worse than power outage. In fact it probably won't affect anyone at all.
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bob wrote:

This is one of those cases where statistics mask the issue. When the power goes out, it's obvious. I go around the house fixing all the clocks that are no longer accurate. Life returns to normal.
Not knowing whether the clock on the wall is correct is a much bigger problem. How often do I have to get out the ladder to climb up and reset the clock?

I'll bet there'll be lots of consequences. The clock on my 40-year-old stove will be affected. And I ain't replacing it...EVER. I'll bet there are lots of legacy timepieces used in employee time clocks, old buildings, etc.
The question is not, whether I'm able to find the correct time. The question is, can I get accurate time from every time indicator in view.
Knowing that most newer devices will not be affected is comforting only to those who don't have legacy devices.
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The 60 Hz has never been the "rock" you think it is. While its long term accuracy is pretty good its short term accuracy isnt that great and very rarely exactly 60hz. As a matter of fact my freq counter says it is 60.07xxx Hz, the xxx means that these digits are constantly chnging. Georgia Power used to give a tour of their Plant Hatch facility and one of the topics mentioned was frequency accuracy. I would like a couple of examples of any products that use the power line frequency as a CRITICAL reference as I know of none.
Jimmie
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