Electrical grid description from c.s.y2k
From: Fred Swirbul
Newsgroups: comp.software.year-2000
Subject: Y2K Induced Electric Grid Failures
Date: Mon, 06 Apr 1998 05:33:51 GMT
Lets say Y2K hits. Lets be optimistic and say only a few
large electric generating units trip. Most of us will still
have power, right? Maybe not, and here is why.
(The following example is based on the US Western Grid. It
is comprised of about 12 states in the western most continental
US, from California to Wyoming, Washington state to New Mexico.
This interconnected grid is "controlled" by the WSCC (Western
States Coordinating Council). The events postulated below are
similar to the August 1996 event that caused power outages for
somewhere in the neighborhood of 25-50% (rough guess, I don't
have the exact number) of the population of those 12 states,
typically for a number of hours)
First, a few basics on large scale electric power generation
and transmission.
1) Power generated must always equal power consumed. If it doesn't,
grid disturbances start to occur. Some may be minor, as when a
car on cruise control hits a small hill. The cruise control
automatically kicks in more gas, and you regain your crusing
speed. The same thing occurs automatically with electric power
managment systems. Some may be larger, as when your car hits a
big hill. Typically you want to take it out of cruise and control
it manually. Manual operations like this occur on the grid, by
starting peaking units (small, rapidly started electric generation
units), or controlling it in other ways (I will skip the really
technical stuff). If you run your car into a wall, your air bag
inflates to hopefully save your life, so you can drive another day.
If the grid is run into a wall, it also has automatic protection
systems (circuit breakers, sort of like in your houme, but much
bigger), to protect the electric generation equipment (to make
power another day), but puts you in the dark for right now.
2) The primary purpose of connecting many electric generating units
together (as seen on the western US grid, and many other places),
is to provide a higher level of reliability, over all (it also
makes it easier to buy and sell power amoung utilities and others,
but that is a whole different topic). If one generating unit trips,
the great multitude of others can typically and easily pick up the
load, and everyones lights stay on. If each electric utility was
its own "island", even one large plant tripping would probably put
everyone in that area in the dark.
So how can only a few large electric generating units tripping off
line cause a large disturbance on the electric grid (making it seem
like it "ran into a wall")?
In the US western grid, the primary reason goes back to the fact
that some areas are net producers of power, and some are net users.
Washington State and Oregon produce a lot of excess power, primarily
hydro-electric. California needs the power (and pays good money for it).
There is a very large transmission line from the northwest to California,
that is often at peak capacity, especially in the summer. Lets say a
few generating plants on the southern part of the grid trip. You might
only initially lose 4 Gigawatts (four big plants) out of the about 100
Gigawatts (again rough number), of power produced on the western grid.
Other plants in other areas try to pick up the excess load, including
the plants that are on the far side of that major north-south transmission
line. Since it is already loaded at near peak, the protective equipment
to those lines will open, protecting the equipment (good), but worsening
the grid disturbance (bad). Power might try to continue to flow from
north to south via other transmission lines (remember, the northwest is
a net power producer, and Californai is a net power user). These lines
can't handle that much power either, and their breakers open. You might
be left with the western grid split into two or three large islands.
But the problem doesn't stop there. All areas are still in the middle
of a grid disturbance. This grid disturbance can cause other plants
to trip while protecting their own equipment from this very disturbance.
Also, remember, power generated must always equal power consumed. The
northwest is producing more power than is needed, the southwest is producing
less. Because this is a fast acting event (just a few minutes once the
big generators trip), human intervention is too slow to help. Generating
units trip off and/or loads (like your home or business) are shed until
power generated roughly equals power consumed. This might stabilize at
about 50% of where things started at (i.e the lights are out for only
half the people).
When an eletrical generating unit trips, it could take hours to days to
get it producing power again, assuming no Y2K problems.
Obviously, the electric utilities know about this problem (at least the
responsible people in my utility do). However, there are no operational
strategies in place yet for the entire western grid to attempt to counter
this type of problem. A single utility typically can not unilaterally decide
to isolate themselves, because of open access laws, and because of contractual
agreements for the power they produce. Of course since it is only a
strategy that needs to be put in place, time is available to make things
better. Unfortunately, since no one knows how many generators will trip off
line due to Y2K, it makes it much tougher to plan for contingencies.
Hope this helps.
As always - I don't represent my emplower.
Fred Swirbul |
