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an electrical device used for frequent closing and opening (up to 1,500 operations per hour) of power circuits carrying direct or alternating current. Contactors are widely used for remote control of machinery and apparatus in DC and AC installations at voltages up to 500–650 volts and currents up to 600 amperes.
Contactors are classified as unipolar or multipolar, depending on the number of contact pairs connected to the power circuit. A unipolar contactor has one pair of contacts, one of which is fixed and the other is movable. The movable contact is fastened to the armature of an electromagnet (with a sucking coil mounted on the core). When the control current flows through the coil the armature is attracted by the core and the contacts are closed. Contactors are usually equipped with an arc quencher, which interrupts the electric arc that arises upon separation of contacts (interruption of an electric circuit carrying a current). A contactor is closed by pressing a push button provided in the supply circuit of the sucking coil. A distinction is made between closing contactors, whose contacts are normally open, and opening contactors, whose contacts are normally closed.
The sucking coil in a contactor draws a current that is insignificant in comparison with the current in the circuit being switched. Both the sucking coil and the contact system in a contactor may operate on direct current, or both may operate on alternating current. Contactors that have a contact system for alternating current and a sucking coil for direct current also exist. In a number of designs, the contacts are locked in their closed position by a latch. Locking contacts, which are structurally connected to the latch, automatically disconnect the power to the sucking coil when the main contacts are closed. In this case the closed position of the contactor does not depend on whether the power is connected to the sucking coil. To open the main contacts of this type of contactor, a separate opening coil is required. Contactors are capable of performing several million switching operations. Contactors are manufactured as self-contained, independently mounted devices and as built-in devices in magnetic starters and industrial machines and installations.
REFERENCESBabikov, M. A. Elektricheskie apparaty, part 2. Moscow-Leningrad, 1956.
Chunikhin, A. A. Elektricheskie apparaty. Moscow, 1967.
V. K. IVANOV