Ac contactor, a commonly used control appliance: in the electrical control circuit, it is divided into control circuit and main circuit. AC contactor is the main circuit that is often used to connect or disconnect motors or other equipment. It can be opened and closed hundreds of times per hour. In circuits, it is often used with buttons.

First, the product selection guide

1, selection point

(1) According to the controlled objects, operation times and use categories of contactors, select the contactors of corresponding categories.

(2) Select according to the rated voltage of the line in the use position.

(3) Select the rated current of the contactor main contact according to the load capacity.

(4) For the voltage level and current type of the attraction coil, the requirements of controlling the power supply should be considered.

(5) The capacity selection of auxiliary contacts should be considered according to the number of interlocking circuits required and the breaking current of the connected contacts.

(6) With regard to the on-off ability of contactors, attention should be paid to the loads in some usage categories, such as capacitors, tungsten lamp and other illuminators, which have large current value and long on-off time, so there should be a margin when selecting.

(7) For the electrical life and mechanical life of the contactor, calculate the required electrical life according to the known average operation times per hour and the service life of the machine. Can not meet the requirements, should reduce the capacity.

(8) When selecting, the environmental temperature, humidity, vibration, dust and chemical corrosion of the place of use should be considered, and different types of contactors should be selected according to the corresponding environment.

(9) The contactor of lighting device should also consider the type, starting current, starting time and long-term working current of the illuminator, and the current selection of contactor should not be greater than 90% of the rated current of electrical equipment (line). For tungsten lamp and lighting equipment with capacitance compensation, the conduction current value should be considered.

(10) The consistency of primary and secondary equipment actions should be considered in the design.

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 AC contactor model is CJ. The model of DC contactor is CZ.

3 structure and working principle of electromagnetic AC contactor

Principle, Selection and Connection of AC Contactor

AC contactors are widely used as circuits to cut off and control power. It uses the main contact to open and close the circuit, and uses the auxiliary contact to execute the control instruction. Generally, the main contact has only normally open contacts, and the auxiliary contact often has two pairs of contacts, which have normally open and normally closed functions respectively. Small contactors are often used as intermediate relays to work with the main circuit.

The contact of AC contactor is made of silver-tungsten alloy, which has good conductivity and high temperature ablation resistance.

Ac contactor is mainly composed of four parts: (1) electromagnetic system, including pull-in coil, moving core and static core; (2) Contact system, including three pairs of main contacts, two normally open contacts and two normally closed auxiliary contacts, linked with the moving iron core; (3) Arc extinguishing device. Large-capacity AC contactors are generally equipped with arc extinguishing devices to quickly cut off the arc and avoid burning out the main contacts; (4) Insulation shell and accessories, various springs, transmission mechanisms, short-circuit rings, terminals, etc.

Working principle:

When the coil is energized, the static iron core generates electromagnetic attraction to attract the moving iron core. Because the contact system is linked with the moving iron core, the moving iron core drives the three moving contacts to run at the same time, and the contacts are closed, thus turning on the power supply. When the coil is powered off, the suction disappears, and the linkage part of the moving iron core is separated by the reaction force of the spring, so that the main contact is disconnected and the power supply is cut off.

Selection of AC contactor:

(1) The equipment is running continuously. The contactor is calculated as 67-75%, that is, the AC contactor of 100A can only control the equipment with the maximum rated current below 67-75A.

(2) The equipment runs intermittently. The contactor is calculated as 80%, that is, the AC contactor of 100A can only control the equipment with the maximum rated current below 80A.

(3) Equipment that works repeatedly for a short time. The contactor is calculated as 1 16- 120%. That is, the AC contactor of 100A can only control the equipment with the maximum rated current below 1 16- 120A.

Also consider the working environment and the structure of the contactor.

It should also be noted that due to fierce market competition, some domestic manufacturers have been cutting corners to reduce costs, such as reducing the wire diameter or even the number of turns in the production of coils, using materials that do not meet the national standard or insufficient thickness and cross section of contacts. This situation is not only reflected in contactors, but also in other products such as short-circuit breakers. As a result, in actual use, the actual load of contactor or short-circuit breaker with the target of 100A can only be 80A or even lower, and the failure rate is very high. Therefore, there is a popular saying that domestic low-end products should be used at a 30% discount on the rated capacity specified on the nameplate!

Connection:

One: Generally, a three-phase contactor has 16 points, three inputs and three outputs, two normally open auxiliary contacts, two normally closed auxiliary contacts and two control points (contactor coils). Output and input correspond, so it is easy to see. If you want to increase self-locking, you need to connect the wire of the normally open auxiliary contact to the control point.

Two: First of all, we should know the principle of AC contactor. He added an external power supply to the coil to generate an electromagnetic field. When the power is on, the contacts are disconnected after the power is off. After knowing the principle, you should find out the contacts of the external power supply, that is, the two contacts of the coil, which are generally at the lower part and both sides of the contactor. Other inputs and outputs are generally in the upper part, which is clear at a glance. Also pay attention to the voltage of the external power supply (220V or 380V), which is generally marked. And pay attention to whether the contact is normally closed or normally open. If there is self-locking control, just arrange the circuit according to the principle.

(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) Selection point:

(1) According to the contactor control object, operation times and use category, select the contactor of the corresponding category. ② Choose according to the rated voltage of the line in the use position.

③ Select the rated current of the contactor main contact according to the load capacity.

④ For the voltage level and current type of the attraction coil, the requirements of controlling the power supply should be considered.

⑤ The capacity selection of auxiliary contacts should be considered according to the number of interlocking circuits required and the breaking current of the connected contacts.

⑥ For the on-off ability of contactors, attention should be paid to the loads in some use categories, such as capacitors, tungsten lamp and other illuminators, which have large current value and long on-off time, so there should be a margin when selecting.

⑦ For the electrical life and mechanical life of contactors, calculate the required electrical life according to the known average operation times per hour and the service life of the machine. Can not meet the requirements, should reduce the capacity.

⑧ The environmental temperature and humidity, vibration, dust, chemical corrosion and other factors in the place of use should be considered when selecting, and different types of contactors should be selected according to the corresponding environment.

Pet-name ruby contactor for lighting device, also should consider the type of illuminator, starting current, starting time and long-term working current, contactor current selection should be no greater than 90% of the rated current of electrical equipment (line). For tungsten lamp and lighting equipment with capacitance compensation, the conduction current value should be considered.

Attending design should consider the consistency of primary and secondary equipment action.

[1] (2) Operation and maintenance: ① During operation, check whether the passed load current is within the contactor rating;

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 the coil lead, and repair it in time if there is welding or burning loss. 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, platinum scale formed by metal vapor will be formed in the contact gap, which will affect the service life of the contactor. [Edit this paragraph] AC contactor working system According to the national standard GB 14048.4-93 "Low-voltage electromechanical contactors and motor starters for low-voltage switchgear and control equipment", AC contactors can be divided into four working systems according to working hours:

(1) Eight-hour working system This is the basic working system. The agreed heating current parameters of contactor are determined according to the working system. Generally, contactors of various series specifications are suitable for the eight-hour working system. This kind of contactor with working system, its main contact can reach thermal balance through rated current when it is closed, but it will be disconnected after eight hours.

(2) Uninterrupted working system This working system is a long-term working system, that is, the main contact is kept closed and carries a stable current for more than eight hours (weeks or even years) without interrupting the current. Contactors are prone to contact oxidation and dust accumulation under long-term working conditions, which will lead to deterioration of heat dissipation conditions, reduction of interphase and relative insulation, leakage and even short circuit. When the working conditions require the contactor to work under this working system, the AC contactor must be reduced in capacity or specially designed, and the model that is not easy to accumulate dust and has a long creepage distance should be selected. In dusty and corrosive gas environment, special attention should be paid to this problem.

(3) Short-time working system Under this working system, the time for keeping the contactor main contact closed is not enough to make the contactor reach thermal balance, and the load period is separated by the no-load period, while the no-load period is enough to restore the contactor temperature to the initial temperature (that is, the temperature of the cooling medium). The standard values of contact power-on time for short-time working system are 3, 10, 30, 60 and 90 minutes.

(4) Intermittent periodic working system Intermittent periodic working system is also a repetitive short-time working system, which refers to the working system in which the closing and opening time of the contactor is too short to make the contactor reach thermal balance. Obviously, the main factor affecting the time life of this kind of contactor is the cumulative operation times. The main parameters describing the intermittent periodic working system are the power-on duration and working frequency. The standard value of electrifying duration is 15%, 25%, 40% and 60%, and the working frequency is divided into eight grades (1, 3, 12, 120, 300 and 600). Usually, the working frequency is1600. Typical equipment includes working machine tools (turning, drilling, milling and grinding), lifting equipment, rolling equipment and centrifuges. The four coke ovens in the coking industry also work intermittently, with heavy tasks. Equipment with operating frequency above 600 times /h belongs to heavy-duty equipment, mainly port lifting equipment similar to coal unloader of our company and some devices on rolling mills.

Different working systems put forward completely different requirements for AC contactors, and the emphasis of selection is naturally different. When selecting contactors for "eight-hour working system" and "short-time working system" equipment, there are few restrictions, just consider that the rated current of the contactor is greater than the actual working current, and put a little margin when the equipment is important. When selecting contactors for "uninterrupted working system" equipment, the ability to prevent dust, leakage and overheating should be considered first, and compact contactors should not be selected (circuit breakers should be used instead if necessary). In order to prevent overheating, the contactor capacity should be enlarged by more than 20%, which is the case of most electrical equipment in large chemical production plants. When selecting contactors for "intermittent periodic working system" equipment with heavy and ultra-heavy tasks, the electrical life of contacts and the mechanical life of operating mechanism should be considered first. The contactors are CJ 12 series (especially suitable for wound motors), CJ20 series or vacuum series. Because the electrical life of contactors can be greatly improved by using capacitance reduction, the starting current of the motor can be simply taken as the rated current of the selected contactor to improve the safety and reliability of the production device.