We h ave examined the parameters of a transmission line and a re ready to
con sider the l ine as an element of a power system. Figure 6.1 s hows a 5 00-kV
l in e h aving bundled conductors. I n overhead lines the conductors are susp e n d e d
from the tower a n d i nsulated from it and from each o t h e r b y insulators, t h e
n u mber of which i s determined b y the vol tage o f the line. Each i n sulator s t r i n g
i n F i g. 6.1 h a s 22 insu lators. T h e two shorter arms above t h e p h ase conductors
support wires usua l ly made of steel. Th ese wires, much smaller i n diameter than
the phase conductors, are not visible in the p ic ture, but they are e lectri c a l ly
connected to the tower and a re therefore at ground potential. These wires are
referred to as shield or ground wires a n d shield the phase con d u ctors from
l ightning strokes.