We have examined the parameters of a transmission line and a re ready to
consider the line as an element of a power system. Figure 6.1 s hows a 500-kV
line having bundled conductors. In overhead lines the conductors are suspended
from the tower and insulated from it and from each other by insulators, the
number of which is determined by the voltage of the line. Each insulator string
in Fig. 6.1 has 22 insulators. The two shorter arms above the phase conductors
support wires usually made of steel. These wires, much smaller in diameter than
the phase conductors, are not visible in the picture, but they are electrically
connected to the tower and a re therefore at ground potential. These wires are
referred to as shield or ground wires and shield the phase conductors from
lightning strokes.