Isolating Switch

an electrical device for the reliable disconnection of certain sections of a high-voltage electrical network when there is no current in them. The use of isolating switches (either alone or in combination with high-speed short-circuiting devices) makes it possible to simplify the arrangement of switching points and transformer substations and to eliminate expensive high-voltage circuit breakers.

In the case of damage to certain sections of a network, the circuit breakers operate first, and then the isolating switches automatically disconnect the damaged section, after which the circuit breakers close again and restore electric power to the rest of the consumers on the network. Isolating switches are also used to disconnect and reconnect unloaded transformers and sections of power lines during operation. An isolating switch must provide a reliable connection in case of a random occurrence of a short circuit in the network. An important characteristic of an isolating switch is a short operate time, particularly the disconnect time, which must not exceed 0.1 sec.

The most promising type of isolating switch is the elegaz (sulfur hexafluoride) switch, with contacts that are sealed inside a housing filled with SF₆. In some designs air circuit breakers in series with arc arresters connect the isolating switches. In such cases, in addition to performing their usual functions, the isolating switches disconnect the current flowing through resistors that shunt the arc arresters. Isolating switches are also used to isolate long unloaded lines.