Transmission
and
distribution
of
electrical energy
5
50m
40 m
30m
20m
10m
33kV l32kV 275 kV 400kV Single Ä Ή'
single double double double 33 kV
circuit circuit circuit circuit ,
v
Steel lattice towers
Wood poles
COMPARISON BETWEEN
OVERHEAD LINES AND
UNDERGROUND CABLES
Pin insulator Suspension insulator
Figure 1.3
Wood supports are red fir impregnated with creosote and may be
in the form of single poles or two poles made into an A or H. In the
UK they are used for circuits up to
33
kV but in other countries lines
up to 250 kV using 50m poles have been erected. Since Britain
imports most of the trees required and each pole
is
in fact a complete
tree trunk, large ground clearances using poles proves to be
extremely expensive.
Towers are made of steel angle section and may easily be fabri-
cated up to almost any height