On Thu, 14 Aug 2003 19:12:04 -0700 Fred Heutte <[EMAIL PROTECTED]> wrote:
It looks like DC may have had a close call - the University of Maryland was dark for about 1 hour, and I have heard several news reports here stating that the local (DC regional) power grid just managed to decouple from wider East Coast grid in time to avoid a collapse here. Regards Marshall Eubanks > > Most of the early rumors about causes of the power failure > have proven incorrect -- fire at a New York City power plant, > etc. > > Most likely is a congestion failure in the Niagara-Mohawk > grid, which covers a large part of New York state and has > feeders across into Canada. > > Congestion failures happen when power flows through a > particular switching station are high, and a component > fails either directly or because of a power surge caused by > a failure elsewhere. > > The imbalance caused by an open or short circuit will then > immediately spread through the rest of the grid unless action > is taken to disconnect, or point failures occur (resulting in fires > and explosions from degradation of power transmission > equipment, transformers, etc., not a pretty outcome at all) -- > or both. In general, transmission grids are designed from a > failsafe perspective, meaning that it is much safer to cause > rolling brownouts or blackouts than to let key components > such as transmission substations or power plants have a > catastrophic failure. > > Since the entire grid has to be in sync and supply and demand > must be in relative parity at all times, the usual strategy in > these cases is to isolate the affected area, "island it" by > shutting down power ingress and egress (tripping safety > breakers at major crossing points), and shutting down > power plants in the vicinity that will have stress failures > if they don't have sufficient load to balance their output. > > The problem is that power travels faster than even the > highest-speed switching equipment can operate, so the > surges causing a cascading failure like this afternoon's can > spread very quickly, like ripples in a pond. > > The weather was hot and humid but completely within > range for the time of year, so this has to be counted as a > "normal accident." It's likely that whatever component > initially failed and triggered the shutdown was within > its usual tolerances and simply had an ordinary breakdown. > Of course, to spread, a massive outage like this also exposes > other weaknesses and hidden dependencies in the system, > which might be other physical components, software, > operator error, etc. > > The system is remarkably resilient in most circumstances, > which is what five-nines or more is all about. But rust never > sleeps, and underinvestment in key transmission corridors in > New England, New York north of Manhattan and in > parts of the Midwest is no doubt an underlying cause. > > As to the root cause of that engineering problem -- the > answer is politics, some of it congressional, and I will say no > more in this forum. > > Fred Heutte > > Portland, Oregon > energy policy analyst and net geek >