Switch is electrical

In. 3. low voltage is subdivided into the everyday and the industrial. The first serve for start and turning off of electrical instruments and devices of alternating current (50 Hz) with the stress to 220 V and the current strength to 10 A. Their design depends on the material used, the designation, artistic, and a constructive solution of instrument (device). Everyday In. 3. they manufacture with the manual and, considerably thinner, with auto. control, mainly for overload protection (on the current). By prom. V. 3. one -, two- and tripolar to the rated currents from several of tens to thousand and use in the chains of the distribution of elektrich. energy in essence for overload protection and short-circuit currents (KZ); they manufacture with manual and auto. control. The latter can have also low-voltage protection: lower than the allowable voltage occurs auto. turning off. To by prom. In. 3. frequently carry also knife switches, rotary switches, contactors, magnetic starters , etc.

In. 3. high voltage are intended for the manual or distants. of operational start and turning off of the devices of high voltage with the normal modes and for the auto. disconnection of these installations in the emergency operations with the currents overloads and the currents KZ. Osn the parameters: the nominal stress (from 3 to 750 kV and above); the rated current (from 100 and to 12 kA and above), which can prolongedly flow through the switch without heating of its parts of higher than the permissible temperature; the current of turning off (to several hundred kA), which characterizes the disconnecting ability v. 3. and determined by the maximum current KZ, which in. 3. one can disconnect with this stress. Sometimes Disconnecting Ability V. 3. they determine conditionally by the interrupting capacity, which can reach several ten Gv.a.

By important parameter v. 3. appears tripping time, i.e. time from the delivery of the command to turning off to the curtailment of current KZ. The less this time, the less the damages and damage as a result KZ. Tripping time is usually equal to 0,06-0,1 s, and in the best models v. 3. it is lowered to 0,03 s. Osn structural elements and the classification of high-voltage in. 3. arc extinctions are determined by method or, it is more precise, by that medium, in which the arc extinction (see oil breaker, air circuit breaker, magnetic cutout) occurs. For each type v. 3. there are most conventional and rational field of applications.

Lit.: H in n and X and n A. A., electrical apparatuses, M., 1967.

A. m. Bronstein, V. t. nezhdanov.