Disconnecting Switch

a high-voltage switching device used to disconnect and switch individual sections of electrical networks when the sections are not carrying a current. It produces a directly visible break in the electrical network. In high-voltage bus-and-switch structures disconnecting switches are used primarily to ensure safety during maintenance and repair work on the disconnected sections. In some cases, moderate currents are interrupted by means of disconnecting switches—for example, the magnetizing currents of low-power transformers or the currents of short, unloaded lines. Disconnecting switches are also used for sectionalizing buses and switching electric lines from one bus system in a bus-and-switch structure to another.

A disconnecting switch consists of movable and stationary contacts mounted on insulators. A movable contact is actuated by using an insulator to connect it with a conductor. Disconnecting switches are classified according to the type of installation (indoor or outdoor), the number of poles (for example, single-pole or three-pole), and the method of control (manual or remote). In electrical networks having a voltage ≥ 110 kilovolts, the movable contacts of the disconnecting switches used are of the pantograph type, and the stationary contacts are mounted on the conductors (buses). To avoid erroneous operation, disconnecting switches are provided with mechanical, electrical, or combination interlocks that prevent the opening or closing of the disconnecting switch when the associated high-voltage switches are closed. Disconnecting switches must be capable of passing the rated load current for a long period. They must have excellent thermal and transient stability when passing short-circuit let-through currents.