On Wed, 14 Feb 2007 05:30:27 +0000 (UTC), (Dave
Martindale) wrote:

Mark Lloyd writes:

That's a very common statistics mistake. That gives you the
probability that all stoves are on at a particular time. What matters
is if all stoves are on at ANY time. There's a really big difference
there (as big as the difference between a millimeter and the width of
the galaxy).

It was a thought experiment. It's clearly *possible* for many more than
the average number of stoves to be on, but as this number increases the
probability of it happening gets vanishingly small - too small to worry
about.

If you want to be more precise, what really matters is the amount of
momentary extra load the system can tolerate (which in turn is a
function of the duration of the overload) and how often the randomness
of the load will cause it to exceed that overload threshold.


What I was trying to say before, is that I'd expect the vast majority
of overloads to be momentary.

For example, if it turns out that increasing the load due to ovens from
100 MW to 150 MW for (say) 10 seconds is enough to take down part of
the distribution system by blowing a fuse or tripping a breaker, and
that event is likely to happen once a year on average, that's a
problem. If this event is likely once every thousand years, you can
ignore it.

Repeat this calculation for different load levels and durations. If
all possible random variation in oven load have virtually no effect on
grid reliability, then it can be ignored.

Dave
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Unlike biological evolution. 'intelligent design' is
not a genuine scientific theory and, therefore, has
no place in the curriculum of our nation's public
school classes." -- Ted Kennedy