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Perspective

Fortnightly Magazine - April 15 1998

believe this one, I'd like to talk to you about some land in Florida.) Reality: There are two kinds of bulk power system reliability: generation reliability (or adequacy) and transmission reliability (or security). Generation adequacy is virtually all anyone ever talks about when discussing reliability (em yet it constitutes less than 10 percent of bulk power system reliability concerns. Transmission security, on the other hand, is responsible for more than 90 percent of all reliability problems. Don't believe me? Quick, think of five or six major blackouts. Which ones involved a generation adequacy problem and which a transmission problem? I'd be very surprised if even one involved generation.

Generation shortages, when they do occur, are usually predictable and controllable; you can use voltage reductions, public appeals or, as a last resort, rotating feeder outages. Transmission contingencies are usually unpredictable and uncontrollable; they happen suddenly, often cascading over widespread areas in a matter seconds. In the 1965 Northeast Blackout, the end was unalterably ordained in less than three seconds.

The market can deal to some extent with generation reliability; mostly through the types of products marketers will offer customers. While acceptability problems may emerge when folks start to get cut off, letting the market act is theoretically possible. This possibility is not true for transmission reliability. There's no way to keep some customers on, no matter how much they're willing to pay, when the bulk power transmission system collapses. Think again of the 1965 Blackout. When the system went down, everybody went down (em even the wealthy folks in their million-dollar condos on Central Park West.

MYTH #7: THE BULK POWER TRANSMISSION SYSTEM IS A HIGHLY UNDERUTILIZED RESOURCE. Reality: Probably more so than any other major industry in the modern world, the laws of physics define and control electric power. Ignore or violate them, and you do so at your own risk. Transmission lines will not neatly load-up proportional to their thermal capabilities. Nor can you "send" the electricity down this line or that as you wish. Power flows over a transmission grid according to the electrical characteristics of the various elements, according to Kirchhoff's Laws. Further, the system must always be operated according to defined criteria so that, at a minimum, no single contingency will cause cascading outages and a blackout. Actual transfer capabilities must be computed and continuously updated as the system goes through its second-by-second changes. In reality, many critical transmission interfaces are loaded at or close to their maximum transfer capabilities most of the time.

MYTH #6: PANCAKING AND LOCATION-BASED PRICING ARE ALL THAT PREVENT POWER TRANSFERS FROM BEAUMONT, TEXAS TO BANGOR, MAINE. Reality: The further you try to go through an interconnection, the more transmission interfaces you'll cross. Thus the more likely it will be that you'll encounter at least one interface that doesn't have available capacity. Then there's the matter of transmission losses (em both watts and VARs (volt-amperes reactive). Losses are equal to current squared times resistance (the inductive reactance for VARs). The further you go, the more electrical resistance you have to pass through (em