Brittle Power- PARTS 1-3 (+Notes) - Natural Capitalism Solutions

Chapter Ten: Power Stations and Grids 137complex electrical properties of transmission lines:Transfer of power at a given voltage can be increased only up to a certain levelbeyond which it becomes impossible to maintain synchronous operation betweengenerators at the...ends [of the line]....Following a disturbance, it is possible for amachine to operate momentarily past the stability limit and then to regain synchronism...,butthis ability is limited and operating conditions are established to maintainoperation within safe limits allowing for the occurrence of some disturbances. 80These limits become more stringent at higher voltages and with longer lines—both characteristic of the trend towards larger, more remotely sited generatingplants, such as those proposed to use Western coal.One form of this stability problem was illustrated in microcosm in the 1977New York blackout. Underground cables, used throughout Con Ed’s area,have large distributed “capacitance”—ability to store an electric chargebetween two separated conductors. This capacitance could produce large voltagetransients if not compensated by series “inductances.” Inductance is theability of an electrical conductor—a coil or just a wire—to store energy in itsmagnetic field. Capacitance and inductance are complementary, and compensating,types of “reactance”—the ability to resist changes in voltage or in current,respectively. Controlling an electrical grid therefore requires not onlykeeping supply and demand in quantitative balance, but also balancing thereactance of the loads and lines to prevent damaging transients and to ensurethat voltage and current do not get badly out of step with each other. That“reactive balancing” is where Con Ed came unstuck.Con Ed’s “black-start” procedures—the sequence of operations for restoringthe grid after a complete power failure—relied on the windings of the main,steadily used generators for about two-thirds of the needed inductive reactance.Because circuit breakers had separated those generators from the grid, none oftheir inductance was initially available for compensation, and inductive compensationin another critical circuit was damaged and unusable. 81 Efforts torestore the grid rapidly in large sections apparently led to series resonanceeffects—strong electrical oscillations at unexpected frequencies—between theunbalanced inductive and capacitive elements. This in turn caused high-voltagetransients, which damaged cables, transformers, and switchgear. 82The tripping of the eight-hundred-forty-four-megawatt RavenswoodNumber Three generator was also caused by cable capacitance. When loadsheddingremoved large inductive loads (motors) which had previously compensatedfor the cable capacitance, the capacitive surge raised voltages to asmuch as eleven and a half percent above normal. The resulting pathologicalvoltage-current relationships confused the generator’s controls so much that it