[QuadList] Mains frequencies, control, similarities to genlocking

Sun Apr 11 11:16:42 CDT 2010

RE: The Cesium/Rubidium standard at CBS:  There are both, I just don't remember which came first. The method of calibration for either of these generators was that one of the guys from the control maint. group (I won't mention his name) would walk by the door to that area at EXACTLY 1800 for dinner.   He has been retired a few years so those standards may be a little off.

DE

G. Keller

-----Original Message-----
From: Ted Langdell <ted at quadvideotapegroup.com>
To: Quad List <quadlist at quadvideotapegroup.com>
Sent: Sat, Apr 10, 2010 2:21 pm
Subject: Re: [QuadList] Mains frequencies, control, similarities to genlocking

On Apr 10, 2010, at 10:53 AM, Chuck Reti wrote:

Not documented anywhere I've looked, but wonder if 60Hz might have been chosen since it correlates with 60sec/min - 60min/hr timekeping.
Did make it easier to do electric clocks!
-- 
Chuck Reti
Detroit MI

Keeping time with motor-based clocks is an interesting situation. See the link and text below.

The process has some elements of pre-framesync Genlock... (Think rubidium) and since this is Saturday, would have been something networks were doing with sports events from remote locations.

Googling "Genlock Remotes" brought up a 2009 patent application by CISCO, the data router people in regard to Genlocking remote video sources:
http://www.wipo.int/pctdb/en/wo.jsp?WO=2009105593&IA=US2009034598&DISPLAY=STATUS

Genlock and framesyncs turn up in the April "CBS Retirees Ramblings" here:
http://www.cbsretirees.com/blog/blogger.html

You'll see a couple of items from Harold Deppe (Sr.,) who was in Maint. at CBS in NYC and is on the QuadList.  We may have the only Father/Son pair of engineers on a video-related discussion list, for all I know.

Back to power for a tad:

The section below on Frequency and Load has me wondering whether it would be practical to monitor the powerline freq., with limit alarms to indicate that a power "event" like a brownout, load shed or blackout was about to happen.

Ted

http://en.wikipedia.org/wiki/Utility_frequency#Long-term_stability_and_clock_synchronization
Long-term stability and clock synchronization
Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1926 and the invention of the electric clock driven by a synchronous motor. Network operators will regulate the daily average frequency so that clocks stay within a few seconds of correct time. In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. Over the course of a day, the average frequency is maintained at the nominal value within a few hundred parts per million.[17] In the synchronous grid of Continental Europe, the deviation between network phase time and UTC is calculated at 08:00 each day in a control center in Switzerland, and the target frequency is then adjusted by up to ±0.02% from 50 Hz as needed, to ensure a long-term frequency average of exactly 24×3600×50 cycles per day is maintained.[18] In North America, whenever the error exceeds 10 seconds for the east, 3 seconds for Texas, or 2 seconds for the west, a correction of ±0.02 Hz (0.033%) is applied. Time error corrections start and end either on the hour or on the half hour.[19][20] A dynamicdemand.co.uk/grid - Real-time frequency meter for power generation in the United Kingdom is available online. Smaller power systems may not maintain frequency with the same degree of accuracy.

Frequency and load
The primary reason for accurate frequency control is to allow the flow of alternating current power from multiple generators through the network to be controlled. The trend in system frequency is a measure of mismatch between demand and generation, and so is a necessary parameter for load control in interconnected systems.
Frequency of the system will vary as load and generation change. Increasing the mechanical input power to a synchronous generator will not greatly affect the system frequency but will produce more electric power from that unit. During a severe overload caused by tripping or failure of generators or transmission lines the power system frequency will decline, due to an imbalance of load versus generation. Loss of an interconnection, while exporting power (relative to system total generation) will cause system frequency to rise. AGC (automatic generation control) is used to maintain scheduled frequency and interchange power flows. Control systems in power plants detect changes in the network-wide frequency and adjust mechanical power input to generators back to their target frequency. This counteracting usually takes a few tens of seconds due to the large rotating masses involved. Temporary frequency changes are an unavoidable consequence of changing demand. Exceptional or rapidly changing mains frequency is often a sign that an electricity distribution network is operating near its capacity limits, dramatic examples of which can sometimes be observed shortly before major outages.
Frequency protection relays on the power system network sense the decline of frequency and automatically initiate load shedding or tripping of interconnection lines, to preserve the operation of at least part of the network. Small frequency deviations (i.e.- 0.5 Hz on a 50 Hz or 60 Hz network) will result in automatic load shedding or other control actions to restore system frequency.
Smaller power systems, not extensively interconnected with many generators and loads, will not maintain frequency with the same degree of accuracy. Where system frequency is not tightly regulated during heavy load periods, the system operators may allow system frequency to rise during periods of light load, to maintain a daily average frequency of acceptable accuracy.[21][22]

Ted Langdell
Secretary

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