The high voltage supply is given to the primary of the transformer through circuit breaker. From the bus-bar various feeders emerge out. The panel for each feeder consists of an isolator switch and circuit breaker. In addition to isolator and circuit breaker, the panel is provided with the measuring instruments. As regards protection of feeders usually reverse power relay is employed. A substation which is used for all voltage levels between 55 KV to 765 KV is called outdoor substation. Such type of substation requires less time for construction but uses more space. The outdoor substations are mainly classified into two types, namely pole-mounted substation and foundation-mounted substations.