SCADA systems are not necessarily pure
software, and quite often do not run on
PCs either (though these days of
cheap hardware and tight-wallet businesses, SCADA PCs are quickly becoming
the norm). Nor, in fact, are they always for
process control. All over the
world, one of the biggest users of SCADA is the
electric power industry.
In a
nutshell, SCADA (in conjunction with a few other things) allows for
remote and/or
automated computer control of the
power grid.
Simple as that.
In more detail, it lives
pretty much up to its name:
Supervisory
Control
And
Data
Acquisition. It allows a
supervisor (usually a person at a
computer console back at the particular utility's
control center) to operate
devices on the power grid, and also
relays to that supervisor/
operator information from the
grid. Now by "devices", this doesn't mean they control your
toaster sitting in your kitchen. This is refering to the equipment most often
housed in the little (or big) unmanned
transformer plants you see sitting off beside the highway or in an
empty field somewhere, which are commonly called
substations. You usually see one of these for every few
suburban blocks or
housing projects. In these substations you've got
circuit breakers,
switches,
fuses,
transformers, and various other things. Also, you have to have
power meters. These aren't the kinds of things you find in your
fuse box at home. We're talking switches and breakers that
handle any range from 13, 24, 68, 138, 345
thousand volts and sometimes several thousand
amps, too.
What SCADA allows is: say you have a
tree limb rip down a
power line, and now you've got a
live wire perhaps sitting in a busy
public street. Using the
Data Acquisition side, an operator can receive at his console
information about a line
fault and voltage/amperage drops from various
meters and equipment designed to see and detect
such things. With Supervisory Control, he can send a
control signal to say a
circuit breaker housed in a substation at one end of the line, telling that circuit breaker to
trip, or
open. It opens, cutting off
power to that line. No more
deadly live wire on the road, just a dead
cable. Now sure, a
repair crew could've done the same thing, but the trick here is that all of this occurred in
minutes, three or four maybe. Having to send a repair crew out could've meant that line may have been live, and
lethal, for much, much longer, especially if the crew can't immediately find where the actual
downed line is. It can even be taken a step further, as the computer systems themselves can be
programmed to react to
situations like this, automatically opening the breaker when the line fault is
detected, thus lowering the live-wire time to possibly a mere 30 seconds.
That's just one aspect of SCADA in the
power industry, and the one I'm most familiar with. It's also used for yet another
acronym,
AGC, for
Automatic
Generation
Control. This basically allows a computer system (with
human supervision) to run the massive power
generation stations far more efficiently than
just people alone can. The computers can take
meter readings from all over the grid to figure how much power (
load) is being pulled, and
generate for that amount. Thus, the power companies save
huge sums of money because they're not generating
more power than is necessary, so it's not so
wasteful. It also protects you, the user on the end of the grid, from
black outs (usually ;) due to under-generation. Both of these were very common
back in the days of manual electric generation.
SCADA in the
power industry has been around for decades, and its use on
PCs is actually relatively new (even against the age of PCs themselves). My company still uses
mainframes dated circa 1978 for their SCADA operations, and I
still have to deal with them. These particular
machines were built for the sole purpose of
being SCADA systems, and they were
far from alone. SCADA was and still is a
huge part of the power industry. These days though, SCADA is indeed becoming less
hardware and more truely just
software, and most often found on PC-like machines. I've encountered
AIX PowerPCs,
DEC Alphas, and even
Windows Server PCs running SCADA and power control systems.
My company recently bought ten
Dell PowerEdge units with
Windows 2000. Loaded with
proprietary SCADA and EMS (Energy Management System) software, they're now a
cluster intended to operate a portion of the
Texas power grid covering at least
a third of the state.
God save us from the
blue screen of death.