any of the electrical devices and apparatus used in starting and braking electrical machinery, changing the direction of rotation, regulating the speed and certain other parameters, and protecting the machinery under abnormal modes of operation. Start-control devices encompass apparatus designed for a wide variety of purposes. Included are switching devices (contactors, circuit breakers, signal switches), current-limiting devices (automatic circuit breakers, current-limit relays, fuses), and regulating devices (rheostats, electric controllers). There are also integrated start-control devices (magnetic starters, integrated contactor panels), devices for control and automation circuits (auxiliary relays, time-delay relays), and circuit controllers (contactor controllers, controllers, position switches, push-on starters).
The operating voltage dictates the classification of motor control devices as high-voltage or low-voltage. The means by which a device exercises control accounts for the device’s classification as nonautomatic (knife switches, rotary switches, controllers) or automatic. The latter category includes devices used in both local and remote (contactors, circuit controllers) control. Start-control devices are also classified according to their make as open, where the parts conducting current are open to touch; enclosed, where the parts conducting current are protected from accidental touching; airtight, where the parts are protected from moisture; or explosion-proof, to be used in explosive media or in atmospheres susceptible to explosions because of dust suspensions. Design features are responsible for an arbitrary classification of the devices as contact, contactless, or combined. In the combined devices, mechanical contacts are used in addition to electronic (mainly semiconductor) systems.
In designing and building start-control devices, consideration must be given to the requirements of thermal stability, reliability, and resistance to wear of the contacts or switching elements and to the strength requirements of the electrical insulation, which must be able to withstand overvoltages and ensure safety of operation and servicing.
REFERENCESChunikhin, A. A. Elektricheskie apparaty. Moscow, 1967.
Chilikin, M. G. Obshchii kurs elektroprivoda, 5th ed. Moscow, 1971.
G. G. NESTEROV