Environmental Engineering Reference
In-Depth Information
will result in cutting the current by 99% and reducing the
resistance losses by the same amount. Edison's DC had
voltages to match the load (a light or a motor) or had to
be reduced to that level by another converter placed in
series or by a resistor that wasted the difference. Raising
voltage and reducing current in order to limit DC trans-
mission losses would have resulted in dangerously high
voltages in houses and factories. In contrast, high-voltage
alternating current (HVAC) is transmitted over long dis-
tances with minimized losses and than is reduced to
acceptably low voltages by transformers.
AC transmission, supported by George Westinghouse
and Sebastian Ferranti, prevailed fairly rapidly; the con-
flict was basically over by 1893 with the Niagara Falls
project designed to deliver high-voltage AC. Generation
of the current at low voltages, its transmission as HVAC,
and its distribution to customers at low voltages were
made possible by the introduction of transformers whose
fundamental designs emerged in the United States (Wil-
liam Stanley and George Westinghouse) and in Hungary
(Ott´ Bl´thy, K´roly Zipernowsky, and Miksa D´ri) be-
tween 1883 and 1886. These simple but flexible and du-
rable devices, converting high current and low voltage
into low current and high voltage, and vice versa, opened
the way for centralized electricity generation and hence
for the enormous economies of scale associated with the
larger sizes of turbines and plants.
All early generating stations produced rotary power for
their dynamos by steam engines. Edison's first New York
station had four Babcock & Wilcox boilers (about 180
kW each) on the ground floor and six Porter-Allen
engines (each 94 kW and 320 g/W) and six large
direct-connected Jumbo dynamos on the reinforced sec-
ond floor of 257 Pearl Street (T. C. Martin 1922). Par-
son's reaction turbine, patented in 1884, soon displaced
these bulky and expensive machines. Seven years later, his
pioneering 100-kW machine rated 40 g/W, more than
80% below the best comparable steam engines. That
ratio fell below 10 g/W by 1914, and it was eventually
brought down to just over 1 W/g for the largest
machines built after the mid-1960s (Hossli 1969).
The quest for cheaper and better illumination was Edi-
son's great incentive for designing a new energy produc-
tion and distribution system, but the largest demand for
electricity lay in the substitution of clumsy, noisy, and in-
efficient steam-powered shaft-and-belt drives used to run
machines by electric motors in scores of industrial enter-
prises. This huge market was unlocked by Nikola Tesla's
designs of a practical AC induction motor, patented in
1888. What Edison, Westinghouse, Parsons, Stanley, and
Tesla accomplished during the 1880s put in place such
solid foundations of a new industry that within two gen-
erations the electric industry became a mature branch of
engineering. Its pioneers would find little incomprehensi-
ble about today's arrangements, although they would
certainly appreciate all the major quantitative and qualita-
tive improvements. Principles remain but, as the follow-
ing contrasts indicate, particulars have changed (Smil
2005a).
The largest turbogenerator sizes increased by 5 OM,
rating as much as 1.2-1.5 GW before reaching a plateau
during the 1980s (fig. 8.11). Working steam pressure
rose from about 1 MN/m
2
for the first commercial units
to 35 MN/m
2
for supercritical turbines introduced in
the 1960s; however, 31 MN/m
2
appears to be the opti-
mum for greatest efficiency gains (fig. 8.11). Steam tem-
peratures rose from 180
C for the first units to 650
Cby
1960, with more recent optima at between 560-600
C.
Coal-fired units (boiler-turbine-generator) account for
most of the largest sizes, and in 2005 coal generated
