Over the past century, the electric power industry continues to shape and contribute to the welfare, progress, and technological advances of the human race. The growth of electric energy consumption in the world has been nothing but phenomenal.
In the United States, for example, electric energy sales
have grown to well over 400 times in the period between the turn of the century
and the early 1970s. This growth rate was 50 times as much as the growth rate
in all other energy forms used during the same period. It is estimated that the
installed kW capacity per capita in the U.S. is close to 3 kW.
Edison Electric Illuminating Company of New York inaugurated
the Pearl Street Station in 1881. The station had a capacity of four 250-hp
boilers supplying steam to six engine-dynamo sets. Edison’s system used a 110-V
dc underground distribution network with copper conductors insulated with a
jute wrapping.
In 1882, the first water wheel-driven generator was
installed in Appleton, Wisconsin. The low voltage of the circuits limited the
service area of a central station, and consequently, central stations
proliferated throughout metropolitan areas.
The invention of the transformer, then known as the
“inductorium,” made ac systems possible. The first practical ac distribution
system in the U.S. was installed by W. Stanley at Great Barrington,
Massachusetts, in 1866 for Westinghouse, which acquired the American rights to
the transformer from its British inventors Gaulard and Gibbs.
Early ac distribution utilized 1000-V overhead lines. The
Nikola Tesla invention of the induction motor in 1888 helped replace dc motors
and hastened the advance in use of ac systems. The first American single-phase
ac system was installed in Oregon in 1889. Southern California Edison Company
established the first three phase 2.3 kV system in 1893.
By 1895, Philadelphia had about twenty electric companies
with distribution systems operating at 100 V and 500-V two-wire dc and 220-V
three-wire dc, single-phase, two-phase, and three-phase ac, with frequencies of
60, 66, 125, and 133 cycles per second, and feeders at 1000-1200 V and 2000-
2400 V.
The subsequent consolidation of electric companies enabled
the realization of economies of scale in generating facilities, the
introduction of equipment standardization, and the utilization of the load
diversity between areas. Generating unit sizes of up to 1300 MW are in service,
an era that was started by the 1973 Cumberland Station of the Tennessee Valley
Authority.
Underground distribution at voltages up to 5 kV was made
possible by the development of rubber-base insulated cables and
paper-insulated, leadcovered cables in the early 1900s. Since then, higher
distribution voltages have been necessitated by load growth that would
otherwise overload low-voltage circuits and by the requirement to transmit
large blocks of power over great distances. Common distribution voltages
presently are in 5-, 15-, 25-, 35-, and 69-kV voltage classes.
The growth in size of power plants and in the higher voltage
equipment was accompanied by interconnections of the generating facilities.
These interconnections decreased the probability of service interruptions, made
the utilization of the most economical units possible, and decreased the total
reserve capacity required to meet equipment-forced outages.
This was accompanied by use of sophisticated analysis tools
such as the network analyzer. Central control of the interconnected systems was
introduced for reasons of economy and safety. The advent of the load dispatcher
heralded the dawn of power systems engineering, an exciting area that strives
to provide the best system to meet the load requirements reliably, safely, and
economically, utilizing state of-the-art computer facilities.
Extra higher voltage (EHV) has become dominant in electric
power transmission over great distances. By 1896, an 11-kv three-phase line was
transmitting 10 MW from Niagara Falls to Buffalo over a distance of 20 miles.
Today, transmission voltages of 230 kV, 287 kV, 345 kV, 500 kV, 735 kV, and 765
kV are commonplace, with the first 1100-kV line already energized in the early
1990s.
The trend is motivated by economy of scale due to the higher
transmission capacities possible, more efficient use of right-of-way, lower
transmission losses, and reduced environmental impact.
In 1954, the Swedish State Power Board energized the
60-mile, 100-kV dc submarine cable utilizing U. Lamm’s Mercury Arc valves at
the sending and receiving ends of the world’s first high-voltage direct current
(HVDC) link connecting the Baltic island of Gotland and the Swedish mainland.
Currently, numerous installations with voltages up to 800-kV dc are in
operation around the world.
In North America, the majority of electricity generation is
produced by investor-owned utilities with a certain portion done by federally
and provincially (in Canada) owned entities. In the United States, the Federal
Energy Regulatory Commission (FERC) regulates the wholesale pricing of
electricity and terms and conditions of service.
The North American transmission system is interconnected
into a large power grid known as the North American Power Systems
Interconnection. The grid is divided into several pools. The pools consist of
several neighboring utilities which operate jointly to schedule generation in a
cost-effective manner.
The electric power industry is undergoing fundamental
changes since the deregulation of the telecommunication, gas, and other
industries. The generation business is rapidly becoming market-driven. The
power industry was, until the last decade, characterized by larger, vertically
integrated entities.
The advent of open transmission access has resulted in
wholesale and retail markets. Utilities may be divided into power generation,
transmission, and retail segments. Generating companies (GENCO) sell directly
to an independent system operator (ISO). The ISO is responsible for the
operation of the grid and matching demand and generation dealing with
transmission companies as well (TRANSCO).
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