[QuadList] Mains frequencies, control, similarities to genlocking

[Gideon4]

Re the 60/50Hz business, one of the Gotchas is transformer overheating, or
to expand,  A transformer designed for 60Hz has slightly less Iron in it
than the comparable 50Hz one. If you have a "budget transformer" in a item
of kit from a 60Hz source, they would often saturate on 50Hz, get hot and
burn out. Been there, done that!

Brian Summers
  -----Original Message-----
  From: quadlist-bounces at quadvideotapegroup.com
[mailto:quadlist-bounces at quadvideotapegroup.com]On Behalf Of Ted Langdell
  Sent: 10 April 2010 19:22
  To: Quad List
  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_clo
ck_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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