Trivial coordinated load shedding scheme for utilities?
E. Michael Smith
net peak demand to the grid when a scheme for trivial coordination of
load shedding occured to me... It is so simple... there must be
something wrong with it...
Make a voltage sensitive outlet. Have a little dial on the side that
lets you set the 'cutout' voltage. There is a normal variation in
the range of voltages on the line anyway, so why not use that as a
feature? Build in some hysteresis and some damping based on time
and it should be stable.
What I think ought to happen: As demand builds to a peak, voltage
starts to sag, just a little. IFF the voltage has sagged below
the 'cutout' voltage for a 'long enough time' for a smart socket,
it signals intent to drop power (on it's rs232 port ;-) and then does so.
After some (setable?) minimum off time, it sniffs the voltage again.
Only when it stays high enough long enough does it come back on.
This should not respond to momentary spikes, dropouts, etc. due to
the time factor. It should respond to long duration voltage sags
due to excess demand. It MIGHT tend to oscillate if the load it
is controlling is a major fraction of the service rating, so one might
have to build in the 'smarts' to do a quick voltage sample after
turn on and base the cut off on a percentage drop from that point
rather than from the idle voltage ...
Since theses are individually set, they should tend to have a sort of
random distribution (avoiding large blocks of stuff cutting in and
out on the grid at a specific manufacturer set voltage...) of when
load is shed.
Since they are distributed, they would respond to the local conditions
on that particular sub-set of the grid.
Aggregate control would tend to be self induced, since the need to load
shed manifests automatically in the voltage on the line. To the extent
that the utility wanted control, it could just drift the voltage up
and down a smidge...
I've got to be missing something. This is just too simple...
Our power distribution unit has a voltmeter on the front. It tends
to wander a bit during the day (+/- a volt or two). What is the
'standard' grid voltage and what is the allowed variation in normal use?
It would seem to me that something like 115v +/- 5 provides more than
enough voltage swing for control and still stays within the expected
voltage range of appliances for proper function.
OK, there is the hair brained idea. Get out the knives and cut
it to shreds...
--
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Don T. Borowski
: I was pondering the problem of charging electric cars without adding
: load shedding occured to me... It is so simple... there must be
: something wrong with it...
:
: Make a voltage sensitive outlet. Have a little dial on the side that
: lets you set the 'cutout' voltage. There is a normal variation in
: the range of voltages on the line anyway, so why not use that as a
: feature? Build in some hysteresis and some damping based on time
: and it should be stable.
:
: What I think ought to happen: As demand builds to a peak, voltage
: starts to sag, just a little. IFF the voltage has sagged below
: the 'cutout' voltage for a 'long enough time' for a smart socket,
: it signals intent to drop power (on it's rs232 port ;-) and then does so.
Well, I guess those of use at the far end of the line from the substation
will have to wait for everyone else to charge their cars first. Just hope
I can get a full charge by morning.
In a system like this, some hysteresis will cause power demand oscillations
by those at the marginal voltage levels. Not good for system stability.
I would prefer a utility-controllable power outlet (at a discounted rate).
So would the utility.
Donald Borowski WA6OMI Hewlett-Packard, Spokane Division
"Angels are able to fly because they take themselves so lightly."
-G.K. Chesterton
Richard Bell
shedding scheme to switch off the chargers for electric vehicles is
that it depends on voltage. When a utilty is generating insufficient
power to meet demand it is the frequency which goes down as the kinetic
energy stored in the rotor is transferred to the grid. How the voltage
changes varies, but for residential systems, the voltage will be constant.
The simplest (cheapest?) coordination scheme would tie the chargers into
cable, so the cable company can relay requests to shed loads, so the
electric vehicle power demand can be adjusted before the power system
stability is threatened. the added bonus to any load shedding agreement
is that the utility will pay you to not use power.
James King
>The first problem with the suggested "trivial" coordinated load
>The simplest (cheapest?) coordination scheme would tie the chargers into
>cable, so the cable company can relay requests to shed loads, so the
>electric vehicle power demand can be adjusted before the power system
>stability is threatened. the added bonus to any load shedding agreement
>is that the utility will pay you to not use power.
I think I saw an article regarding a recent court ruling (in the US) which
would allow our beloved local phone companies to compete for this service. :-)
--
Jim
#include <disclaimers.h>
ahs...@dukepower.com
John De Armond
>The first problem with the suggested "trivial" coordinated load
>shedding scheme to switch off the chargers for electric vehicles is
>that it depends on voltage. When a utilty is generating insufficient
>power to meet demand it is the frequency which goes down as the kinetic
>energy stored in the rotor is transferred to the grid. How the voltage
>changes varies, but for residential systems, the voltage will be constant.
Actually utilities reduce voltage in order to drop load (V**2/R works
very much in their favor), commonly known as a brownout, while the
frequency remains constant. Not only is the grid very "stiff" relative
to frequency, the utilities consider maintaining accurate frequency to be
a top priority.
>The simplest (cheapest?) coordination scheme would tie the chargers into
>cable, so the cable company can relay requests to shed loads, so the
>electric vehicle power demand can be adjusted before the power system
>stability is threatened. the added bonus to any load shedding agreement
>is that the utility will pay you to not use power.
The system already implemented for air conditioners and water heaters
is RF-based. The digitally addressable receivers cost <$75 in quantity.
One or two high power, high site transmitters will cover most cities.
TVA calls the program Cycle'n'Save - or did until they drove it in the
ground with corruption.
John
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Carl J Lydick
=In article <CDpME...@watserv1.uwaterloo.ca> rlb...@sunee.uwaterloo.ca (Richard Bell) writes:
=>The first problem with the suggested "trivial" coordinated load
=
=
=>The simplest (cheapest?) coordination scheme would tie the chargers into
=>cable, so the cable company can relay requests to shed loads, so the
=>electric vehicle power demand can be adjusted before the power system
=>stability is threatened. the added bonus to any load shedding agreement
=>is that the utility will pay you to not use power.
=
=
=I think I saw an article regarding a recent court ruling (in the US) which
=would allow our beloved local phone companies to compete for this service. :-)
Actually, it's not clear which (if any) of the extant agencies would best
handle this. The information superhighway (proposed by Bush, supported by
Clinton [though I seriously doubt that either had a clue as to what it's all
about]) would allow what you're talking about. Any reasonable implementation
would have your electric utility buy a channel on the network to do this (or
could allow the electric utility to superimpose communications on the power
distribution network [nah, that'd make too much sense]).
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: CA...@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL
Disclaimer: Hey, I understand VAXen and VMS. That's what I get paid for. My
understanding of astronomy is purely at the amateur level (or below). So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it. If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.
Mark O. Wilson
|would have your electric utility buy a channel on the network to do this (or
|could allow the electric utility to superimpose communications on the power
|distribution network [nah, that'd make too much sense]).
The power network is optimized for 60 Hz. Get substantially above that
and the attenuation gets fierce.
Not only that, but you would need a high frequency bridge across every
transformer in the system.
--
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It ain't charity if you are using someone else's money.
Wilson's theory of relativity: If you go back far enough, we're all related.
Mark....@AtlantaGA.NCR.com
John De Armond
>In <27rq6b...@gap.caltech.edu> ca...@SOL1.GPS.CALTECH.EDU (Carl J Lydick) writes:
>|could allow the electric utility to superimpose communications on the power
>|distribution network [nah, that'd make too much sense]).
>The power network is optimized for 60 Hz. Get substantially above that
>and the attenuation gets fierce.
>Not only that, but you would need a high frequency bridge across every
>transformer in the system.
Hate to tell you this but "carrier current signalling" has been standard
in the utility biz since the early 50s. That is, signalling modulated
onto a (typically) 100 khz radio carrier that is then coupled to the
power line. The signal IS bypassed around and choked out of transformers and
other switchgear. The carrier current chokes (actually parallel resonant
tanks) are plainly visible on the leads of many substation transformers.
Carrier current is currently used for protective relaying coordination
and occasionally for an intercom channel between opposite ends of a
transmission line.
Bringing carrier current to the house would be simple and would require
little in the way of new hardware. Less expensive would be to use
carrier current to bring control signals to neighborhood and then
break it out on low power 900 mhz radio received by receivers connected
to the controlled loads.
Of course the Cycle'n'Save scheme I previously posted about is even
cheaper.