Load Disconnect

high-voltage electric switching gear used for rapid connection and disconnection of electric circuits operating under normal conditions, and also of load circuits and no-load power lines and transformers. Under emergency conditions a load disconnect must also withstand the short-circuit current of the circuit in which it is installed; in such situations it must have sufficient dynamic and thermal strength to withstand the let-through short-circuit currents flowing through its current-carrying system.

Since load disconnects are not intended for interruption of short-circuit currents, their arc-arresting parts and drive mechanisms are much simpler and their cost lower than those of other high-voltage breakers. The most common arc arresters in load disconnects are those that use a solid arc-arresting substance, elegaz (sulfur hexafluoride), as well as vacuum arc arresters and those with magnetic blowout. High-voltage fuses are usually installed in series with load disconnects to protect electrical equipment from short-circuit currents. In a radial distribution network a main breaker is often installed at the origin point of the transmission line as a protective device, and load disconnects are installed on the branches. In the event of a short circuit in one of the branches, the main breaker opens, followed by the lead disconnect of the damaged branch; the main breaker can then be reclosed and power supplied to all other users. Other network connection circuits with load disconnects are also in use.