Automatic Switching of Incoming Lines and Transformers Supplying Power to A-C. Substations

The early applications of automatic switching were confined principally to equipment which supplied or handled the outgoing power, such as conversion apparatus and outgoing feeders. As the field broadened and the capacity of the stations increased, it became necessary to provide for greater continuity of incoming power. In order to meet this requirement it has been customary to bring in two, and occasionally three, incoming lines. It is the purpose of this paper to describe briefly some of the more common forms of this type of automatic switching. By making a few minor modifications of the schemes which are described it has been possible to control automatically a complete loop or ring system. Balanced power or parallel incoming lines are quite common. Ordinarily two such lines are used, although as many as six have been contemplated. All lines are usually carrying power to the substation unless a fault has developed. When cleared of the fault, the line (or lines) is automatically replaced in service. In the case of the preferred-emergency type of equipment, it is customary for one line (the preferred) to carry the substation load. The second line (emergency or standby) takes this load upon failure of the first line. The application of these units to a system usually determines the sequence of operation between the two lines. A few typical combinations are described and illustrated. A brief description of automatic synchronizing and transformer switching has been included.