The structure and principle of AC Contactor

The contactor is an electromagnetic automatic switch. It is used for frequent starting and remote control of motor, which makes the operation more safe and convenient. Contactor is one of the main low-voltage appliances which are widely used. Contactor is operated by electromagnetic force, according to the operating power source can be divided into dc and ac two categories. The two structures are roughly the same. Figure 1 is the physical object of the contactor, figure 2 is the internal structure of the contactor, character symbol.

1. Structure of ac contactor the contactor shown in figure 2 is composed of upper and lower sections, and the upper section is a thermosetting plastic body. The auxiliary contact, main contact and arc extinguishing device are fixed above; The lower section is a thermoplastic base on which the electromagnetic system and buffer device are installed. The base is provided with screw holes and the lower part is provided with a lock for IEC standard 35mm slot rail. 1. Electromagnetic system. The electromagnetic system is composed of coil, "E" shaped static core and armature core. The head of the static core is equipped with a short circuit ring to prevent the armature from vibrating when ac current flows through zero.

2. The contact part includes three pairs of main contact and four pairs of auxiliary contact. The main contact is composed of three groups of bridge moving contacts and three pairs of static contacts on the upper and lower sides. The contact is made of silver-based alloy, which has a larger capacity and allows a larger current to connect and disconnect the main circuit. Static contact, static core, coil into one, bridge type moving contact and armature into one. Contact is divided into normally open (NO) and normally closed (NC). When the coil is energized at the end, the contact in the breaking state is called normally open contact. A contact in a closed state is called a normally closed contact. The number of normally open (NO) and normally closed (NC) contacts in the four pairs of auxiliary contacts of the contactor can be arbitrarily combined. Auxiliary contacts are only allowed in control circuits with low current.

3. The arc extinguisher is equipped with an arc extinguisher in the ac contactor with the arc extinguisher current over 40A, whose function is to limit the arc generated when the main contact is broken, so as to avoid contact sintering or fusion welding.

Working principle of contactor when ac voltage is applied to both ends of the coil (called coil electricity), the stator core of the coil generates electromagnetic suction, which attracts the armature to drive the bridge contact downward and make it contact with the static contact on both sides (suction). If the three static contacts on the upper side are connected to a three-phase power supply and the three static contacts on the lower side are connected to a motor, then the three-phase power supply is connected to the motor to start and run since the bridge contacts have connected the static contacts on the upper and lower sides. When the coil power off, electromagnetic suction disappeared, under the action of spring force moving contact and static contact separation (release). Cut off the power, and the motor stops. Therefore, as long as the control contactor coil voltage on and off, can easily control the start and stop of the motor. Figure 2 b) shows the electrical symbol of the contactor. It includes main contact, auxiliary contact and coil. The main contact and the auxiliary contact have different graphic symbols, but the text symbols are KM.


Post time: Dec-08-2019