(AP) WASHINGTON (AP) - A yearlong experiment with the nation's electric grid
could mess up traffic lights, security systems and some computers - and make
plug-in clocks and appliances like programmable coffeemakers run up to 20
minutes fast.
"A lot of people are going to have things break and they're not going to
know why," said Demetrios Matsakis, head of the time service department at
the U.S. Naval Observatory, one of two official timekeeping agencies in the
federal government.
Read more:
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So will shop motors run slower or faster ?
Best Regards
Tom.
Worst case scenario: East coast clocks at 20 minutes/year.
60 Hz *60 sec. *60 min. *24 hr. *365 day = 1892160000 cycles in a year
20 minutes of extra cycles:
60 Hz * 60 sec. * 20 min. = 72000 cycles
72000 divided by 1892160000 = 3.805175038051750380517503805175e-5
or in non exponential terms: .00003805 which is .003805 percent
frequency change. I doubt if any machine motors will notice the
difference. The same with almost all digital clocks, which use a crystal
to set the frequency, not the grid. Maybe your grandfather's Westclox
electric alarm, with the motor, but even most of them were/are self
correcting, each time you adjust the time, they get a little bit more
accurate.
Both.
As I understand it, the grid frequency isn't perfectly constant now
and they have to tweak it to make the count of seconds in an hour or
day come out right.
I've built and tuned phase-locked-loops that synchronized to the power
line for precision measuring instruments. At that location the grid
was stable enough that I didn't see momentary frequency variations,
just a lot of SCR switching noise around the zero crossings.
A previous job had been out in the country near a ski resort. Their
200 HP snowmaking machine affected the grid enough that we bought a
generator to run the product for acceptance testing.
jsw
"East Coast clocks may run as much as 20 minutes fast over a year, but
West Coast clocks are only likely to be off by 8 minutes. In Texas,
it's only an expected speed-up of 2 minutes." This proves three
things, though everybody already knew them as facts:
1)There -is- such a thing as a New York Second
2) They're slow down in Texas.
and
3) The West Coast is Weird.
A tad faster, if anything. You'll be more efficient in the shop, Tom.
--
You can't wait for inspiration. You have to go after it with a club.
--Jack London
I have a Westclox LED digital alarm clock that runs twice as fast when
I'm on the generator. The generator regulates within about 5 Hz so
maybe it double-triggers on noise at the zero crossings. It doesn't
like inverter AC either.
I depend on 'atomic' battery clocks to set the off-line computer for
TV recording. As long as the government doesn't mess with atoms I
should be OK.
jsw
All the traffic light controllers I've seen are microprocessor
controlled, and use a crystal for their reference. Does "Cars won't
start and elevators won't work. All power plants will shut down at
midnight because of Y2K" ring any bells?
There's still lots of electronics-less units here in Chicago. It's
impressive they last years and years just slamming contacts back and
forth, all run from a timing motor.
What is the poing of the frequency variation in the first place? it's
never explained in the links.
A control systems group at our university tried to understand the stability
of the electrical grid. This was a big, multi-year DOE grant. They wrote
a software simulation, with generating plants, loads and transmission lines.
As I understand it, they eventually found that the problem is essentially
mathematically intractable, but that they were able to establish certain
bounds to the solution. What that all means is that the grid is not really
very stable at all, somewhat like a whole bunch of masses tied together by
a network of springs, and energy being added and subtracted here and there.
Resistance of the transmission lines and the huge resistance of resistive
loads (incandescent lights and toasters) may be the only thing keeping it
from going wildly unstable. They do experience periods of smaller
instability now and then, and sometimes have to pull a generating station
offline to break the cycle of reactive power bouncing back and forth from
one region to another.
So, with that background, **I THINK** what is going on is they think there
may be a way to reduce some of these stability problems if they don't
try to maintain exact frequency all the time, TOO. Stability is a LOT
more important than minor frequency variations.
Jon
r.
It is some what bogus any way.
The frequency is not stable, ever, it is a CONSTANT dance. Add more
load, the whole system slows down (a very little) drop some off, it
speeds up. Increase the governor of any power plant, it speeds up
too, the reverse if you reduce the governor. The actual frequency
meanders quite a bit in the short term, but is constantly being
"pushed" towards an intended average.
As far as the coasts being different, it is simple. We are not all one
grid, and some parts that are tied together, are tied with DC links.
Not as bad as Saudi Arabia used to be, with one side of the country at
60 Hz and one at 50. But I've heard that they fixed that.
jk
Think about a 60 HZ standing wave....
HOW can that be applied to the grid? It cannot.
Say for example, you had a reference signal leaving Minneapolis, and
the peak of that wave will arrive in Chicago some time later. If there
is only One single line between these two centers, no problem...
Now add in the grid. The peak of that 60 HZ sine wave arrives at
Chicago, and the peak is also traveling from Minneapolis to Denver,
then on to Chicago.... The time is not the same for the two possible
paths.. There needs to be power moving back and forth...
With the wavelength of signal smaller than the possible distances in
the grid, you cannot have it all tied together without recirculating
power...
Even if a reference signal was assigned to one point in that example,
the reference cannot arrive at various points in the grid intact
because being a grid, there are multiple paths for it to follow.
Now add in multiple sources driving the grid, and you are left with
recirculating power... There is no way to have a "master" reference
for the grid...
The ONLY way that I can think of it working would be if all the
connecting points were assigned a time stamp reference from a MASTER
signal, and you would need tapped Delta transformers at each end of a
line.
Moving the delta taps could force power to flow in either
direction...
A tapped Delta transformer can change the phase angle, without
changing the voltage.
Can anyone illuminate this situation?
Anytime I have talked to electric power guys, they have never heard of
or thought about the fact that the grid cannot be in sync, without
having recirculating power..
They always refer to the grid has an infinite source and sink of
reactive power... it gobbles up the MVARS, or supplies them to keep
the generator perfectly in sync. You can open or close the wicket
gates to push more or less power to the grid. The voltage and
frequency are locked, but pushing harder against it will push more
amps... or pushing softer will push less amps...
When the grid frequency is constant all the ferroresonance circuits that can
blow up due to standing waves do it as they are each energized. If you vary
the frequency the ferroresonance parts will suddenly appear at random and
the grid would become very unstable. This sound like grid suicide. Many
pieces of equipment would not like it.
e.g. High voltage BPD, CVTs or Pot-coupler devices. (Bushing potential
devices, Capacitive voltage transformers, potential coupled devices). These
high voltage step down transformers rely on capacitive coupler to take a
"tickler" current off a high voltage line, typically in transformer bushings
as the lead passed through the long insulated tube inside a transformer
bushing. The resulting "
trickle" current is passed through a series of "tuned" circuits (RLC) to
produce a phase and ratio accurate reproduction of the high voltage to be
used in protection and/or metering circuits. These take high tech equipment
analysis to set them up using the resonant tuned circuits involved. Changing
the applies frequency would shift the phase of the protection circuits and
the line would get a trip command sent down the communication circuits to
open the transmitting ends.
The Eastern Seaboard Grid System has massive groups of Engineers working on
these grid synchro problems and the whole self-interest group concepts is a
waste of time and mostly nonsense. These circuits already have multiple
layers of massive, complex, protection schemes to protect against this kind
of thing and history has produced a need for constant improvement of the
technology and sophistication of these protection schemes. Contact a Senior
P&C Engineer at Hydro One or IESO and you can haggle this out with him until
after he retires, and then some, and still not come to a solid conclusion
for improvement.
-------------
Think about a 60 HZ standing wave....
HOW can that be applied to the grid? It cannot.
Say for example, you had a reference signal leaving Minneapolis, and
the peak of that wave will arrive in Chicago some time later. If there
is only One single line between these two centers, no problem...
Now add in the grid. The peak of that 60 HZ sine wave arrives at
Chicago, and the peak is also traveling from Minneapolis to Denver,
then on to Chicago.... The time is not the same for the two possible
paths.. There needs to be power moving back and forth...
With the wavelength of signal smaller than the possible distances in
the grid, you cannot have it all tied together without recirculating
power...
Even if a reference signal was assigned to one point in that example,
the reference cannot arrive at various points in the grid intact
because being a grid, there are multiple paths for it to follow.
Now add in multiple sources driving the grid, and you are left with
recirculating power... There is no way to have a "master" reference
for the grid...
The ONLY way that I can think of it working would be if all the
connecting points were assigned a time stamp reference from a MASTER
signal, and you would need tapped Delta transformers at each end of a
line.
Moving the delta taps could force power to flow in either
direction...
A tapped Delta transformer can change the phase angle, without
changing the voltage.
Can anyone illuminate this situation?
Anytime I have talked to electric power guys, they have never heard of
or thought about the fact that the grid cannot be in sync, without
having recirculating power..
They always refer to the grid has an infinite source and sink of
reactive power... it gobbles up the MVARS, or supplies them to keep
the generator perfectly in sync. You can open or close the wicket
gates to push more or less power to the grid. The voltage and
frequency are locked, but pushing harder against it will push more
amps... or pushing softer will push less amps...
It is Not really "recirculating", but what IS happening is PHASE
shift.
You can have a single frequency (with a "master" reference, and still
have as many paths as you want. You WILL have phase shifts between
points, but so what?
I am one, perhaps you were not understanding their response.
Not true, they will be in "sync" from a frequency point of view, but
not in phase.
Frequency is "locked"ish, but the voltage is not!
You change your local voltage [To a degree] by varying exitation. You
also change the level of vars you exchange with the system.
If you are not paralleled with a system, then all you change is the
voltage, if you are connected to a very stiff part of a system, all
you really cahnge is vars.
Not entirely. YOu puch more power or less power, which means more or
less amps, but you can push more amps by vary8ing exitation and hence
the vars. So it is POSSIBLE to push more power, and fewer vars and
end up at the same amps (Within some farily small limits)
IF you are not connected to a system, opening the gate just increases
frequency (=speed ) if your load takes more power at a higher
frequency it will also generate more power. If not, then your speed
will increase until something destroys itself, or speed related losses
reduce the accelerating torque to 0, or an overspeed device kicks in
to shut the gate.
jk
It would make no difference to traffic light timers driven by synchronous
motors anyway. They are all tied to the same grid. So if they all ran at
60.1 Hz the traffic lights would be synchronized for 30.05 MPH instead of
30.
I think its got to do with the wind generation lobby. Back in the old days,
the grid's total cycle count was brought back to a 'true' 60 Hz count by
adding or subtracting generation (usually at night) to
accelerate/decelerate the grid as required. But wind sources are
notoriously unstable and the requisite trimming efforts would be greater
and fall on primarily the thermal plants. The wind people have thrown a few
hissy fits on the occasions when grid stability could not be maintained and
they were asked to shut down. So this appears to be a compromise to allow
wind generation to coexist on the grid without imposing costs on them or
thermal plant operators.
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