The mechanical endurance is the critical characteristic of Magnetic Contactors, which are widely used in such industrial equipments as elevators, cranes, and factory control rooms in order to close and open the control circuit.
Magnetic contactors are mainly located in the end of the power distribution system, meaning the nearest position of the electrical load. Magnetic Contactors are composed of a magnetic component, a contact point and some frames to hold them which is illustrated in figure 1.1.
Figure 1.1 A Schematic Diagram Of Magnetic Contactors
The voltage and current capacity of the magnetic switches for alternating current range from 220V-11A to 690V-5A and also from 220V-800A to 690V-630A, respectively. In the field operation, the magnetic switches are generally used below 690V-800A.
Magnetic contactor consists of electromagnetic coil, several stationary contacts, and auxiliary contacts (NO contacts and NC contacts). The function of stationary contacts is as a connector between terminal motor with the voltage source. Stationary contacts have larger contact and those are on a center position. These contacts are shown with 1,2,3,4,5,6 symbols. Auxiliary contacts serve as the part of control circuit. Among its function is as the locker and as contacts to lamp indicators. These contacts are shown with 11,12,13,14 symbols for NO and 21,22,23,24, and so on for NC. But the last number is always 1 until 4. The magnetic coil are shown with A1-A2 symbols which will work , if the coil gets the voltage source.
Figure 1.2 Magnetic Contactor
The Characteristics Of Magnetic Contactor
a. The power capability of contactor must be written in Watt/KW which is adapted by the load.
b. The ability to draw the current from the contacts, Written in ampere .
c. The ability of voltage from the magnetic coil, whether for 127 volt or 220 volt, so also its frequency.
d. The ability to protect against the low voltage.
The Applications of Magnetic Contactors
a. Lighting control
Contactors are often used to provide central control of large lighting installations, such as an office building or retail building. To reduce power consumption in the contactor coils, latching contactors are used, which have two operating coils. One coil, momentarily energized, closes the power circuit contacts, which are then mechanically held closed; the second coil opens the contacts.
b. Magnetic starter
A magnetic starter is a device designed to provide power to electric motors. It includes a contactor as an essential component, while also providing power-cutoff, under-voltage, and overload protection.
c. Vacuum contactor
Vacuum contactors utilize vacuum bottle encapsulated contacts to suppress the arc. This arc suppression allows the contacts to be much smaller and use less space than air break contacts at higher currents. As the contacts are encapsulated, vacuum contactors are used fairly extensively in dirty applications, such as mining.
d. PLC(programmable logic control)
With magnetic contactors, automatic and semiautomatic control is possible with equipment such as programmable logic controllers.
References :
Petruzella (1996). Industrial Electronics.Singapore: McGraw Hill.
Haeng-Soo Ryu, Gyu-Hwan Han, and Nam-Sik Yoon. (2007).”Basic Study of Degradation Test for Magnetic Contactors and Reliability Centered Maintenance”. Journal of Electrical Engineering and Technology.2.441-444.
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