Environmental Engineering Reference
In-Depth Information
year 2000 (USDOE 2001). FBC stations can have power
densities in excess of 5 kW
e
/m
2
.
During the twentieth century the power of the largest
transformers increased 500 times, and their voltage about
15 times, while their weight/power ratio declined by 1
OM, and their efficiency reached practical limits at over
99% (Coltman 1988; Smil 2005a). U.S. transmission
started with wood poles, cross arms, and solid copper
wires at a mere 4.6 kV and rose in a series of leaps: 6.9
kV, 23 kV, 69 kV, 115 kV, 230 kV, 345 kV, 500 kV,
765 kV. Transmission corridors widened from just over
10 m for 115 kV to 40 m for 765 kV, but the exponen-
tial increase in power loading of three-phase, 60-Hz lines
means that the latter link will have more than 50 times
higher capacity. Typical rates for the land taken over by
tower pads and access roads, and hence unavailable even
for cropping or grazing, range between 10,000 m
2
/km
and 15,000 m
2
/km.
DC transmission came back for undersea cables and
long-distance connections between large, remote hydro-
generating stations and major load centers. In 1954 the
pioneering Sweden-Gotland cable carried 20 MW at
100 kV over 96 km; the first English Channel crossing
in 1961 had a capacity of 160 MW at G100 kV; and
New Zealand's two islands were connected in 1965 by a
G250 kV tie carrying 600 MW. The West Coast Pacific
Intertie in 1970 carried 1440 MW at G400 kV over
1330 km, followed in 1972-1977 by Manitoba's Nelson
River-Winnipeg link (1620 MW at G450 kV over 890
km) and in 1976 by Zaire's Inga-Shaba line (560 MW
atG500 kV over 1700 km). These ties were surpassed in
the late 1980s by the link between Itaip´ hydrostation
and S˜o Paulo (G600 kV over 800 km).
