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. [1][ Edit this paragraph] Basic classification AC contactors can be divided into electromagnetic type, permanent magnet type and vacuum type.
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. [ 1]
Structure and working principle of permanent magnet AC contactor
(1) structure:
Contactor is mainly composed of drive system, contact system and arc extinguishing system.
① Drive system: The drive system, including electronic module, soft iron and permanent magnet, is an important part of permanent magnet 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, transmission mechanism, etc.
(2) Working principle:
Permanent magnet AC contactor is a kind of micro-power contactor, which uses the principle of like repulsion and opposite attraction to replace the traditional electromagnet drive mechanism with permanent magnet drive mechanism. The permanent magnet with fixed polarity installed on the contactor linkage mechanism interacts with the soft magnet with variable polarity solidified on the contactor base to achieve the purpose of attraction, retention and release. The polarity change of soft magnet is that the electronic module solidified with it generates positive and negative pulse currents of ten to twenty milliseconds, thus generating different polarities. According to the needs of the site, the set release voltage can be controlled by the control electronic module, and the reverse pulse current can be sent out after a period of delay, so as to achieve the purpose of low-voltage delayed release or power-off delayed release, thus preventing the motor controlled by it from jumping and stopping due to power grid shaking and maintaining the stability of the production system.
(3) Features:
The innovative technical feature of permanent magnet AC contactor is to replace the traditional electromagnet drive mechanism with permanent magnet drive mechanism, that is, the control device composed of permanent magnet and microelectronic module replaces the electromagnetic device in traditional products, and there is no working current in operation, only a weak signal current (0.8- 1.5mA). Microelectronics module consists of six basic parts: 1. Power supply rectification; 2. Control the real-time detection of power supply voltage; 3. Release energy storage (some also have pull-in energy storage, but not necessarily); 4. Energy storage capacitor voltage detection; 5. Anti-interference threshold voltage detection; 6. Release the logic circuit. These six parts are necessary parts of the electronic control part of the permanent magnet operating mechanism. If any part is missing, the operating mechanism will not work normally in some cases. These six parts also determine that the operating mechanism can have anti-sloshing function.
(1) energy saving:
The closing maintenance of traditional contactor is realized by overcoming the opening spring by the electromagnetic force generated by the closing coil. Once the generated electromagnetic force is insufficient to overcome the reaction force of the spring, the contactor cannot remain closed. Therefore, the traditional AC contactor closing maintenance must be maintained by the continuous energization of the coil, and the current varies from tens of milliamps to thousands of milliamps. The permanent magnet AC contactor relies on the permanent magnet force, which does not need the coil to generate electromagnetic force through current, and only has the working current of 0.8 Ma- 1.5 Ma of the electronic module, so it can save electricity to the maximum extent, and the power saving rate is as high as 99.8%.
②. No noise:
The traditional AC contactor closes the silicon steel sheet by energizing the coil, so that the static and dynamic silicon steel sheets attract each other. When the power grid voltage is insufficient or the surface of dynamic and static silicon steel sheets is uneven or there are dust and foreign objects, noise will be generated. The closure of permanent magnet AC contactor is maintained by permanent magnet force, so there will be no noise.
③. No temperature rise:
Traditional contactors rely on coils to generate enough electromagnetic force to maintain attractive force. The coil is composed of resistance and inductance, and it will inevitably heat up if the current is applied for a long time. On the other hand, the magnetic flux in the iron core will also generate heat. These two kinds of heat work together in the contactor cavity, which often burns out the contactor coil and reduces the capacity of the main contact. Permanent magnet AC contactor is maintained by permanent magnet force. Without the maintenance coil, there is naturally no temperature rise.
(4). Contact fatigue:
The attraction of traditional AC contactor is realized by energizing the coil, and the attraction is related to current and magnetic gap. When the voltage fluctuates in the critical state of closing and opening, the contactor is in the state of sharing and closing, which will constantly vibrate, resulting in contact welding or burning, and motor burning out. However, the attraction of permanent magnet AC contactor is completely realized by permanent magnet force, and the attraction is completed at one time, so the voltage fluctuation will not affect the permanent magnet force, and the main contact will not be burned due to vibration, so the possibility of burning the motor is greatly reduced.
⑤ Long service life and high reliability;
The life and reliability of contactor are mainly determined by the life of coil and contact. The traditional AC contactor will generate heat when working, especially when the voltage, current and magnetic gap increase, which will easily lead to heat and burn the coil, while the permanent magnet AC contactor does not have the possibility of burning the coil. Contact ablation is mainly caused by arc generated during opening and closing. Compared with the traditional contactor, the permanent magnet AC contactor not only has the same electromagnetic force, but also has permanent magnetic force, so the closing speed is much faster than the traditional AC contactor. According to the test, the closing time of permanent magnet AC contactor is generally less than 20ms, while the closing speed of traditional contactor is generally about 60 ms. When opening the brake, permanent magnet AC contactor not only has the function of opening spring, but also has the function of magnetic pole repulsion, which makes the opening speed much faster than that of traditional contactor. According to the test, the opening time of permanent magnet AC contactor is generally less than 25ms, while the opening speed of traditional contactor is generally more than 80 ms In addition, the heating of coil and iron core will reduce the capacity of main contact, and insufficient suction or vibration caused by voltage fluctuation will make the main contact of traditional contactor heat, arc and even weld. Compared with the traditional AC contactor, under the same conditions, the contact life of permanent magnet AC contactor is prolonged by 3-5 times.
6. Anti-electromagnetic interference:
The permanent magnetic circuit used in permanent magnet AC contactor is completely sealed and will not be disturbed by external electromagnetic interference during use.
7. Intelligent anti-sloshing:
The control electronic module controls the set release voltage value, and can send out reverse pulse current after a certain delay, so as to realize low-voltage delayed release or power-off delayed release, prevent the motor controlled by it from jumping and stopping due to grid voltage fluctuation (power flicker), and maintain the stability of the production system. In particular, enterprises with continuous plant production can reduce the consumption of electricity, steam and natural gas, and reduce labor costs, equipment damage and repair costs. [Edit this paragraph] Use connection 1: Generally, a three-phase contactor has eight points, three inputs, three outputs and two control points. Output and input correspond, so it is easy to see. If you want to add self-locking, you need to connect the wire from one terminal of the output point 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][ Edit this paragraph] Model classification in electrical technology. Contactor is an automatic switch, which is used to connect or disconnect the AC /DC main circuit with load or the large-capacity control circuit. The main control object is motor, which is also used for other electric loads, such as electric heaters, electric welding machines, lighting equipment, etc. Contactor can not only make and break the circuit, but also has the function of low voltage tripping protection. The contactor has great control ability. Suitable for frequent operation and remote control. It is one of the important parts of automatic control system. General contactors can be roughly divided into the following two categories.
1 AC contactor. There are mainly electromagnetic mechanisms. Contact system. Arc extinguishing device, etc. . Commonly used is CJ 10. CJ 12 .CJ 12B and other series.
2 DC contactor, generally used to control DC electrical equipment, DC passes through the coil, and the action principle and structure of DC contactor are basically the same as that of AC contactor.
But now the contactor model has been reclassified. They are all AC series. . . 1; AC- 1 contactor is used to control non-inductive or micro-inductive circuits.
2; AC-2 contactor is used to control the start and break of wound asynchronous motor.
3; AC-3 and AC-4 contactors can be used to frequently control the starting and breaking of asynchronous motors [Edit this paragraph] Selection and maintenance selection ① According to the controlled objects, operation times and use categories of contactors, select the corresponding types of contactors. 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. Maintenance ① Check whether the passing 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, platinum scale formed by metal vapor will be formed in the contact gap, which will affect the service life of the contactor. [2][ Edit this paragraph] Operation and use 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 work system
This working system is a long-time 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, which is enough to make the contactor temperature return 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 work system
Intermittent periodic working system, that is, repeated short-time working system, refers to the working system in which the closing and opening time of contactor is too short to make 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.