The principle and structure of Contactor

Contactor is an electrical instrument used to remotely control switching, reversing and overload protection (if there is a thermal relay) asynchronous three-phase squirrel cage induction motors.

A contactor that includes one item called a conventional starter to switch off the electric motor. Booting from two Contactor is a dual-purpose starter that changes the direction of the engine, called a reversing start. For short circuit protection, a fuse must be fitted.

Sort startup word:

Classification Contactor in the cabinet according to the following characteristics:

According to the principle of transmission: we have electromagnetic Contactor (electromagnetic induction), press type, hydraulic type. Usually in the cabinet use electromagnetic Contactor.

– In the form of current: Contactor one-way and Contactor AC (Contactor 1 phase and 3 phase).
Rated voltage of the coil: 36V, 127V, 220V, 380V, 500V.
– Structural protection against impact by the surrounding environment: openness, protection, dust, water explode …
– Ability to change the direction of the electric motor: No rotation reversal and rotation reversal.
– Number and type of contact: Open, usually closed.

Structure and operation principle:


The Contactor is composed of the following components: electromagnetic structure (electromagnet), arc cut system, contact system (main and auxiliary contacts)

A) Electromagnet:
The electrification consists of four components:

– Coils used to create magnet attraction.

– The iron core (or magnetic circuit) of the magnet consists of two parts: the fixed part and the movable cap. The magnetic steel core may be of EE, EI or CI type.

– Spring springs push the lid back to full mobile position

B) Electric arc control system:

When the Contactor in the switchboard switches, the electric arc appears as the contacts are burnt, worn out. Therefore, it is necessary to have a metal articulated system with two metal contacts next to each other, especially at the contactors of the contactor in the cabinet.

C) Contactor contactor system in control cabinet.

The Contactor contactor system in the electrical panel connects the core from the mobile to the mechanical interconnect. Depending on the load capacity of the contacts, one can divide the Contactor contacts into two types:

It is possible for large currents to pass through (from 10A to several thousand A, for example, about 1600A or 2250A). The main contact is the open contact normally closed when the power supply to the Contactor circuit in the cabinet causes the circuit from the Contactor to suck.

– Additional contact of the Contactor in the cabinet: Capable of passing current through contactors less than 5A. The secondary contact has two states: the normally closed and open contacts of the contactor in the cabinet.

The normally closed contact is a closed contact type (contact between two contacts) when the magnet coil in the contactor in the cabinet is in a resting state (no power supply). This contact opens when Contactor is active. The opposite is usually open contact.

Thus, the main contactor of the control panel is usually mounted in a dynamo circuit, while the auxiliary contacts are mounted in the control circuit of the Contactor in the electrical panel (which controls the supply of power to the coils). The magnet wire of the Contactor according to the predetermined process).

According to some common Contactor structures in the cabinet, the subcontractors in the cabinet can be fixedly connected in the number of each Contactor, but there are also some fixed-numbered manufacturers. The main contactor on each contactor, and the auxiliary contacts in the switchboard are made up of individual loose units. When needing to use only to add on the Contactor, the number of auxiliary contacts in this case can be arranged in the cabinet is optional.
Operating principle:

1.a) Boot word and two buttons:

2 lines of music
The Jumpstart diagram

When supplying the winding voltage by pressing the start button M, the Contactor windings have a mobile steel core suction power and the magnetic circuit closes: Close the main contacts to start the motor and close the normally open contact. To maintain the control circuit when the hand release from the start button. When the D stop button is pressed, the start-up is switched off, under the effect of a compression spring, returning the moving core back to its original position; The contacts return to normal mode. Engine stopped working. When there is a motor overload problem, the thermal relay will cause the winding circuit breaker to interrupt the starting and stopping of the electric motor.

B) Boot from reversing and three buttons
When the MT push button is pressed, the Contactor T is electrically driven by the steel core and the magnetic circuit is closed; Close the main contacts T to start the forward rotary motor and close the normally open contact T to maintain the control circuit when letting go of the MT start button.

To reverse the motor rotation, press the MN button to make the Contactor T coil
Electric, Contactor N coils are electrically suction mobile steel core and closed loop magnetic resistor; Closing the main contacts N, now on the reverse circuit of the two wires in the three phases, reversing the motor reversing and the normally open contact N to maintain the control circuit when let go from the trigger button Animated MN.
Rotation reversal is repeated as above.
When the D stop button is pressed, the N (or T) power is turned off, the engine stops.
When there is a motor overload problem, the thermal relay will cause the winding circuit breaker to interrupt the start and stop of the electric motor.
Diagram: image of kdt


Asian. Rated voltage of Contactor in the cabinet

Nominal voltage of Contactor Nomad is the voltage of the circuit in the control cabinet corresponding to which the main contact must be switched off, which is the voltage applied to the two windings of the electromagnet so that the magnet is drawn back.

Supply voltage rating in the cabinet: 110V, 220V, 440V one-way and 127V, 220V, 380V, 500V alternating.

B. Rated current of the Contactor in the cabinet

The rated current of the Contactor in the Ion cabinet is the rated current passing through the main contact in the long-term working mode.

The rated current of the Contactor in common low voltage cabinets are: 10A, 20A, 25A, 40A, 60A, 75A, 100A, 150A, 250A, 300A, 600A. If placed in the cabinet, the rated current must be lowered by 10% due to poor cooling, the current passed through the Contactor must be lowered in the long-term working mode.

Selection and assembly startup from:
Three-phase asynchronous motors can work continuously depending on the reliability of the startup. Therefore, the verb must satisfy the following technical requirements:
– High abrasion resistance.
– Ability to close – high cutting.
– Operation close – cut decisively.
– Low power consumption.
– Motor protection is not overloaded (thermal relay).
Currently in our country, three-phase asynchronous squirrel cage induction motors with a capacity of 0.6 to 100KW are widely used. To control their operation, we usually use the word start. Therefore, to facilitate the start-up selection, the manufacturer usually not only provides the rated output power but also the power of the electric motor that starts from the service of other voltages. together.
For start-up from reliable work, when mounting, it is necessary to secure the hard starting of the boot from a vertical plane (inclination allowed against the vertical axis 50), not allowing the grease to the contacts and sets. reactionary. After starting the installation from and before operation, the following must be checked:
– For manual moving parts that are not jammed.
– The control voltage must match the rated voltage of the coil.
– The contacts must be in contact and good.
– The wiring must follow the control diagram.
– The thermal relay must be set to start from the fuse according to the protection fuse.

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