Ground wires are also referred to a variety of names such as shield wires and sky wires. These are bare conductors located above the phase conductors, at the top of the transmission towers.
The main purpose of these conductors is to protect the transmission lines from lightning. They serve to shield the line and intercept lightning stroke before it hits the current carrying conductors below.
Ground wires normally do not carry current. Therefore, they are often made of steel. The ground wires are solidly connected to each tower. These conducting towers serve as down conductors for lightning current.
By protecting the line from lightning, the design of apparatus in substations is simplified due to lower stress on insulation.