Newsgroups: sci.energy
From: John De Armond
Subject: Re: Trivial coordinated load shedding scheme for utilities?
Message-ID: <2zpzf6@dixie.com>
Date: Wed, 22 Sep 93 21:11:41 GMT

rlbell@sunee.uwaterloo.ca (Richard Bell) writes:

>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

Newsgroups: sci.energy
From: John De Armond
Subject: Re: Trivial coordinated load shedding scheme for utilities?
Message-ID: <hrsznhf@dixie.com>
Date: Sat, 25 Sep 93 16:40:13 GMT

mwilson@ncratl.AtlantaGA.NCR.COM (Mark O. Wilson) writes:

>In <27rq6bINNt2u@gap.caltech.edu> carl@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.

John