454 AC POWER SYSTEMS
concerns seem to demand inherently safe reactor designs with standardized, modular construction
of nuclear units. Since the major U.S. hydroelectric sites (except in Alaska) have been fully
developed, one can foresee a trend for continuing percentage decline in hydroelectric energy
generation.
By the year 2000, the total U.S. generating capacity has reached 817 GW (1 GW=1000 MW)
and continues to grow. Current lead times of about a decade for the construction and licensing of
large coal-fired units may cause insufficient reserve margins in some regions of the United States.
As of 1989, U.S. transmission systems consisted of about 146,600 circuit-miles of high-
voltage transmission. During the 1990s, additions have totalled up to 13,350 circuit-miles, which
include 230-kV, 345-kV, and 500-kV lines. Because of the right-of-way costs, the possibility of
six-phase transmission (instead of the current three-phase transmission) is being looked into.
U.S. distribution-network construction is expected to increase over the next decade. The older
2.4-, 4.1-, and 5-kV distribution systems are being converted to 12 or 15 kV. Higher distribution
voltages such as 25 and 34.5 kV are also contemplated.
Recently some concern has surfaced about the effect of electromagnetic waves on the human
and animal environment. The result of this remains to be seen.Computers in Power Systems
The control and stability of any electric power system is indeed extremely important, in particular
when a system is expected to maintain uninterrupted continuity of service within set limits
of frequency and voltage, and to guarantee reliability of the system. Digital computers and
microprocessors, along with highly developed software programs, have made their way into
planning, designing, operating, and maintaining complex interconnected power systems. A large
volume of network data must also be acquired and accurately processed. Digital computer
programs in power-system engineering include power-flow, stability, short-circuit, and transients
programs.
For a network under steady-state operating conditions, power-flow programs compute the
voltage magnitudes, phase angles, and transmission-line power flows. Today’s computers are
capable of handling networks with more than 2000 buses (nodes) and 2500 transmission lines
in less than 1 minute power-flow solutions. Interactive power-flow programs have also been
developed along with CRT displays.
Stability programs are used to analyze power systems under various disturbances. Short-
circuit programs compute fault currents and voltages under various fault conditions. These, in
turn, will help in circuit-breaker selection, relay coordination, and overall system protection.
Transients programs yield the magnitudes and shapes of transient overvoltages and currents
that may result from lightning strikes and other surges on the system. Based on the results of such
studies, insulation coordination and surge-arrester selection are configured.Planning and Research
Energy research worldwide is assuming top priority, in particular because of economic, en-
vironmental, and resource constraints. DOE (Department of Energy) was established in the
United States in 1977. A major private utility sponsored energy research organization, EPRI
(Electric Power Research Institute) in Palo Alto, California, has been in existence since 1972.
In addition, large utility companies, such as AEP (American Electric Power), have their own
research programs.
The major goals for the future are: