1 usage classification

Contactor is an automatic control device. Contactors are mainly used to frequently connect or disconnect DC circuits, with large control capacity and remote operation. Relays can realize timing operation, interlocking control, various quantitative control and under-voltage protection, and are widely used in automatic control circuits. Their main control objects are motors, and they can also be used to control other electrical loads, such as electric heaters, lighting, electric welding machines, capacitor banks and so on.

According to the type of control current, contactors can be divided into AC contactors and DC contactors. This paper mainly introduces the commonly used AC contactors. AC contactors can be divided into electromagnetic type and vacuum type.

2 model description

(1) The above models are standard models. In recent years, B series AC contactors have been newly developed, and the model is BXX.

(2) The model of electromagnetic AC contactor is CJ. The model of vacuum AC contactor is CZ.

3 structure and working principle of electromagnetic AC contactor

(1) structure:

Contactor is mainly composed of electromagnetic system, contact system and arc extinguishing system.

① Electromagnetic system: The electromagnetic system, including electromagnetic coil and iron core, is an important part of the contactor, which drives the contacts to close and open.

② Contact system: Contacts are the executive parts of contactors, including main contacts and auxiliary contacts. The main contact is used to connect and disconnect the main circuit and control the larger current. The auxiliary contact is in the control circuit to meet the requirements of various control modes.

(3) Arc extinguishing system: The arc extinguishing device is used to ensure that the arc generated when the contact leaves the circuit is reliably extinguished, so as to reduce the damage of the arc to the contact. In order to quickly extinguish the arc when it is disconnected, contactors are usually equipped with arc extinguishing devices. Generally, semi-closed longitudinal ceramic arc extinguishing cover is adopted, and it is equipped with strong magnetic arc blowing circuit.

④ Other components: insulation shell, spring, short-circuit ring, transmission mechanism, etc.

(2) Working principle:

When the electromagnetic coil of the contactor is not energized, the reaction force of the spring and the self-weight of the armature core keep the main contact disconnected. When the electromagnetic coil is connected to the control voltage (usually rated voltage) through the control loop, the electromagnetic force overcomes the reaction force of the spring to attract the armature to the static core, which drives the main contact to close the circuit and the auxiliary contact to move with it.

4 AC contactor selection and operation and maintenance

(1) Select:

(1) The rated current of the main circuit contact should be greater than or equal to the rated current of the controlled equipment, and the starting current of the motor should also be considered when controlling the contactor of the motor. In order to prevent the main contact of frequent contactor from ablation, the rated current of frequent contactor can be reduced.

(2) The rated voltages of the contactor electromagnetic coil are 36V, 1 10V, 220V, 380V, etc. The electromagnetic coil is allowed to be used in the range of 80% ~ 105% of the rated voltage.

(2) Operation and maintenance: ① Check whether the passed load current is within the contactor rating during operation: 1;

2) Whether the opening and closing signals of the contactor are consistent with the circuit state;

3) Whether the running sound is normal and whether there is any discharge sound with poor contact;

4) Whether the electromagnetic coil is overheated and whether the electromagnet short-circuit ring is abnormal.

5) Whether the arc extinguishing cover is loose or damaged;

6) auxiliary contact with and without burning;

7) Whether the transmission part is damaged;

8) Whether there are unfavorable factors such as excessive vibration, poor ventilation and excessive dust in the surrounding working environment.

② Maintenance:

When maintaining electrical equipment, contactors should be maintained together.

1) External maintenance:

A. clean external dust;

B. Check whether the fastener is loose, especially the conductor connection part, to prevent the contact from loosening and heating;

2) Contact system maintenance:

A. Check whether the positions of dynamic and static contacts are aligned and whether the three phases are closed at the same time. If there is any problem, adjust the contact spring;

B. Check the degree of contact wear, the wear depth shall not exceed 1mm, and replace the contact in time if it is burnt or falls off after welding; When slightly burned, it generally does not affect the use. Sandpaper is not allowed to be used when cleaning contacts, and plastic files should be used;

C. Measure the insulation resistance between phases, and the resistance value shall be not less than10mΩ; ;

D. Check whether the auxiliary contact moves flexibly, and the contact stroke should meet the specified value. Check whether the contacts are loose and fall off. If problems are found, repair or replace them in time.

3) iron core part maintenance:

A. Remove dust, especially the dust between the moving parts and the contact surface of the iron core;

B. check the fastening of the iron core. Loose iron core will increase running noise;

C. If the iron core short-circuit ring falls off or breaks, it should be repaired in time.

4) electromagnetic coil maintenance:

A. measure the insulation resistance of the coil;

B. Whether the coil insulation is discolored or aged, and the surface temperature of the coil should not exceed 65℃; ;

C. Check the connection of coil leads, and repair them in time if there is welding or burning. 5) local maintenance of arc extinguishing cover:

A. check whether the arc extinguishing cover is damaged;

B. Whether the position of the arc extinguishing cover is loose or not, and whether the position changes;

C, removing metal particles and sundries in the gap of the arc extinguishing cover.

5 working principle of vacuum AC contactor

Vacuum contactor uses vacuum as arc extinguishing medium, and the main contact is sealed in a special vacuum arc extinguishing tube. When the operating coil is energized, the armature is attracted, and the contact is closed under the action of the contact spring and the self-closing force of the vacuum tube; When the working coil is powered off, the reaction spring overcomes the self-closing force of the vacuum tube, releases the armature and disconnects the contact. When the contactor breaks the current, metal vapor will form in the contact gap.

References:

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