IEEE Power & Energy Magazine - May/June 2017 - 85

through much of the 20th century,
the history of electric power in north
America was characterized by the growth
and consolidation of individual power
systems into large and more intricate
networks, utilizing higher and higher
transmission voltages; a photo of a typical high-voltage transmission line is
shown in figure 2. by 1965, there
were four synchronous interconnections, or grids, in north America. the
largest, called the eastern interconnection, extended from the northeastern
United States and Ontario to the gulf
of mexico and from the Atlantic Ocean
almost to the rocky mountains. the
second largest stretched from the rockies west to the Pacific and was called
the Western interconnection. two areas,
most of the state of texas and the entire
province of Quebec, remained separate
grids. they, as well as the Western interconnection, were (and still are) tied
to the eastern grid by dc lines, and by
these and other means, power can be
shipped back and forth among the four
grids, despite the lack of ac ties be-

The U.S. Federal Power Commission
The FPC was created in 1920 by the Federal Water Power Act. Originally, its
primary responsibility was the licensing of hydroelectric projects on navigable
waterways owned by the U.S. government. It did not consist of commissioners in the usual sense; rather, it was chaired ex officio by the secretaries of
War, Interior, and Agriculture. In 1930, the FPC was reorganized as an independent commission of the U.S. government, with five members nominated by
the president and confirmed by the Senate. It also regulated interstate electric
utilities and the natural gas industry. The FPC was again reorganized in 1977 as
the Federal Energy Regulatory Commission, preserving its independent status
within the newly created Department of Energy.

tween them. the various north American synchronous interconnections are
depicted in figure 3.
the power flow on interconnected
ac systems is directly proportional to
the sine of the electrical angle between
two adjacent generators connected to
the grid. this makes the behavior of
ac systems unlike more familiar phenomena. Power flow between adjacent

generators will increase as the angle
increases; in fact, this is exactly how
systems are controlled. normal power
system operation is very low on the
sine curve, making the relationship essentially linear. however, as the 90°
point is approached, things become
nonlinear. As the angle increases, the
corresponding increase in power flow
becomes less and less. then, from 90°

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2017