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AC contactor for pump application. A contactor is an electrically controlled switch used for switching an electrical power circuit. [1] A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt coil electromagnet controlling a 230-volt motor switch.
Korndorfer starter with motor (M), autotransformer (AT) and three switches (1, 2, 3) In electrical engineering, the Korndorfer starter is a technique used for reduced voltage soft starting of induction motors. The circuit uses a three-phase autotransformer and three three-phase switches. This motor starting method has been updated and improved ...
Typically, the voltage is controlled by reverse-parallel-connected silicon-controlled rectifiers , but in some circumstances with three-phase control, the control elements can be a reverse-parallel-connected SCR and diode. [2] [3] Another way to limit motor starting current is a series reactor. If an air core is used for the series reactor then ...
NEMA (National Electrical Manufacturers Association) contactors and motor starters are rated by sizes. These sizes are grouped by rated current and power. [1] [2]
Motor control centers are usually used for low voltage three-phase alternating current motors from 208 V to 600 V. Medium-voltage motor control centers are made for large motors running at 2300 V to around 15000 V, using vacuum contactors for switching and with separate compartments for power switching and control. [3]
For three phase motors, this is achieved by swapping the wires connecting any two phases. Single phase AC motors and direct-current motors often can be reversed by swapping two wires but this is not always the case. Motor starters other than 'DOL' connect the motor through a resistance to reduce the voltage the motor coils get on start up.