response 75 of 99:

Aug 28 13:28 UTC 2003

Re #71: That's sometimes done; it's called "islanding".  There are two
problems, though, as I understand it.  One is that the local utility may
simply not have the generating capacity to carry the load once they're
isolated from the grid.  Another is that it becomes difficult to get the
islands back in phase to reconnect them later, without shutting
everything down.

Re #72: Automatic under-frequency load shedding was supposed to have
been implemented after the major blackout in the 70's, but obviously the
systems aren't as effective as people had hoped.  The major blackouts on
the west coast in the 90s (some of which actually did end with the west
coast seperating into three "islands") showed that sequencing automatic
controls so that they trip in a way that limits damage, instead of
causing it to cascade through the system, is difficult.  We don't seem
to be able to model the behavior of these complicated power grid systems
very well.

response 79 of 99:

Aug 28 19:12 UTC 2003

From: <BreakingNews@MAIL.CNN.COM>
Subject:      CNN Breaking News

Major power outage hits south London, cutting subway service 
during evening rush hour.

response 85 of 99:

Aug 29 01:54 UTC 2003

Re: #75
The local utility doesn't need to have enough generating capacity active
"on the island" when they cut it loose from the grid...IF they have the
ability to both measure usage in and blackout a fair number of smaller 
parts of the island.  X times per second, a computer in their central 
switching HQ solves the problem "if we cut to being an island right now,
which pieces of load and/or supply would have to immediately cut to have
our island's grid viably balanced?".  If the larger grid gets too bad to
hand onto, then the computers simultaneously cut off from it and off from
the load and/or supply that the island can't keep up right now. 

Where do the power plants get their 60Hz reference from now?  Or is it
just a brute-force "democratic vote" of the local references on a variety
of pieces of equipment?  Sounds like syncing islands to rejoin is a "we
never bothered to make control systems for that" problem.  

response 87 of 99:

Aug 29 05:32 UTC 2003

I don't know where they get their reference, but I do know that the
frequency wanders during the day, such that clocks that use synchronouos
motors vary daily by several minutes (mostly partly corrected overnight -
see http://web.ukonline.co.uk/freshwater/clocks/synch.htm).

response 99 of 99:

Aug 30 13:30 UTC 2003

Re #73:  Keeping service running appears to be the mantra, and the
grid operators do not like systems which can malfunction and bring
things down.  Blackouts make customers very unhappy and trigger
penalty clauses.
                                                                               
                                       
I largely disagree with the assertions of the governor of New Mexico and others
who claim that we have a third-world electrical grid.  Far from it!  Ours is as
good as anywhere in the world.  What we have, unfortunately, is a *dumb*
electrical grid, with dumb appliances connected to it.  The only way to remedy
a sudden loss of generation is to cut customers off.  There is no segregation
of loads into critical (like computers, medical equipment and traffic lights)
and non-critical (like air conditioners, washing machines and outdoor sign
lamps).  Some office buildings have such distinctions in their wiring (certain
circuits on a generator feed), but that only makes a difference once the grid
power has gone off.

If Cleveland could have dumped half their air-conditioners at the
first sign of trouble and modulated demand to keep their plants and
wires running within limits, there would have been no problem; most
people probably wouldn't ever have noticed.  A given wire carries
power from zero to max to zero in 8.33 milliseconds, but the system's
intelligence takes a goodly fraction of a minute to do anything on a
really good day.  If we are going to keep cutting margins in the
name of market efficiency, that has to change.
                                                                               
                                       
Syncing an alternerator is about as easy as Tod represents.  All you need to do
is connect it to the line through a resistor, and it will be automatically
pulled into phase.  (This is assuming you aren't using something like a
grid-synchronous inverter, which you can buy off the shelf in ratings of a
couple hundred watts on up.)  So long as you aren't applying more power than
the line impedance can carry without losing sync, you're fine.  Once the
alternator is in phase you can cut the resistance to zero and start making
serious power.

Some generators, such as induction generators, take their sync from
the line and require no attention in that regard.  However, they can't
run stand-alone without some fairly sophisticated measures.
                                                                               
                                       
Re #85:  If I do not misunderstand, California was reduced to a set of islands
by various failures last decade.  It seems likely that the eastern seaboard was
also islanded by the failure of 8/14.  Those islands certainly were
synchronized, quickly and professionally.