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RE: East Coast outage?
Load management is actually fairly common here in Ohio in the cooperative electric utilities. Residential users get rebates on heat pumps and water heaters in exchange for allowing the utility to install RF controlled interrupting switches on them. Summer ironically isn't the problem for them, its winter when they want to do peak demand management so as not to ratchet into a higher wholesale demand rate class. My guess is when it shakes out, the failure will be traced to a rather large unit or interconnect tripping offline. Since the load is relatively constant if you look at the time in a short enough period, and you lose a couple hundred MVA of feed onto the grid, the other generation on the grid is going to attempt to absorb it. It works just like a drill, in reverse. If you put a sanding wheel onto a drill and press it into wood, it will drag the drill down. Opposite for generation. Steam is driving the turbine, which is producing power. Throw more load on instantaneously, the rotor will slow down. Now the units can absorb slight variations in load, but 500MVA falling off quickly cannot be instantaneously absorbed. So, the rotor slows down. As it slows down, the frequency drops. When the frequency gets low enough (and we're talking fractions of a Hz), protective relaying kicks in and opens the breaker between the unit and the grid. This compounds the effect, because the 500MVA loss may cause another 100MVA in units to trip off relatively close. Now the grid has 600MVA to absorb and that loads more units down, which drift farther down and they trip, which adds another X MVA to the load and it justs keeps going. Same thing can happen in reverse to when the load is suddenly removed and the unit overruns the frequency. This effect was observed a couple of times for a muni electric I used to work with. They had a tie line to a IOU and when it opened in the summer becuase of lightning, overload, etc, it would trip all their units off line because the tie was carrying inbound on the order of 40% of their load. Interestingly, it had effects on the IOU also, since the muni was consuming watts, but supplying VAR's, trying to help maintain power factor on the IOU system. Units can only produce so many MVA's. MVA = sqrt(MW ** 2 + MVAR ** 2). As reactive loads go up (like AC units in the summer), MVAR's go up. According to the formula, MW production goes down since the unit can only produce so many MVA's (its a nice right triangle, MVA is the hypotenuse, MW is the horizontal and MVAR is the vertical and power factor is the cosine of the angle. With a purely resistive load like a light bulb, PF = 1 since there are no VAR flows there [cos 0 = 1]). They do cheat sometimes and use capacitors or synchronous condensors/reactors (an overexcited motor which looks like a variable capacitor, kind of cool) to try and equal out the power factor. The bite is, Joe Consumer doesn't pay for VAR's, he pays for Watts. But the transmission and distribution system has to account for and carry the VAR flows also. And if you size the lines and forget the VAR flows, in the summer, things can go boom. Everyone whines because of the "antiquated" system. The system worked like it should. It may suck to be without power for 48 hours, but try 18 months if the unit came apart. You don't go to Ace Hardware and buy a new 50MVA steam driven unit. And the nukes tripping off was probably more an artifact of frequency instability on the grid than a problem with the nukes themselves. Coal, gas or nuke, you still have to maintain frequency. As an old EE prof of mine said, the system will seek stability. Seeking may be nice like flow re-distribution, or it may be ugly like the rotor and frame separating. Either way, it ends up stable (albeit maybe in the field next to the plant) ... > -----Original Message----- > From: email@example.com [mailto:firstname.lastname@example.org]On Behalf Of > Iljitsch van Beijnum > Sent: Friday, August 15, 2003 6:25 PM > To: email@example.com > Cc: nanog list > Subject: Re: East Coast outage? > > > > On vrijdag, aug 15, 2003, at 23:58 Europe/Amsterdam, firstname.lastname@example.org > wrote: > > > Amount of energy generated must be balanced with the amount of energy > > used > > at any time. Otherwise Bad Things (tm) will happen. The shutown of the > > grid is a very good thing compared to what it would have been had it > > not > > shutdown. > > It seems to me that the power guys are still living somewhere in the > last century. Is it really impossible to absorb power spikes? We can go > from utility to battery or the other way around in milliseconds, so it > should be possible to activate something that can absorb a short spike > much the same way. Balancing intermediate-term generation/usage > mismatches should be possible by simply communicating with users. There > is lots of stuff out there that switches on and off periodically (all > kinds of cooling systems, battery charging, lights), so let it switch > on or off for a few minutes when the power network needs it to. > > I think the idea that the power should be always present and always > reliable is actually harmful, as it doesn't provide for any "congestion > contnrol" by bringing the users into the loop. > >