The contactor is a highly versatile automatic electromagnetic switchgear, which is an important low-voltage electrical appliance in electric drag and automatic control systems. It can frequently contact and segment AC and DC main circuits and large-capacity control circuits. The main control object is the electric motor, and it can also control other equipment such as electric welding machine, electric resistance furnace and lighting equipment. It uses the pull-in and reverse-elastic action of the electromagnetic force to close and break the contact point, thereby turning the circuit on and off. It features undervoltage release protection and zero voltage protection with large control capacity for frequent operation and remote control. It is reliable in operation, long in life, stable in performance and easy to maintain. The contactor cannot cut off the short-circuit current and is therefore usually used in conjunction with a fuse.
The working principle and structure of the contactor
The contactor is mainly composed of an electromagnetic system, a contact system, an arc extinguishing system and other parts.
(1) Electromagnetic system: The electromagnetic system includes an electromagnetic coil and an iron core, and is an important component of the contactor, and relies on it to drive the closing and opening of the contact.
(2) Contact system: The contact is the execution part of the contactor, including the main contact and the auxiliary contact. The main contact is switched on.
(3) Break the main circuit to control the large current, and the auxiliary contact is in the control loop to meet the requirements of various control methods.
(4) Arc extinguishing system: The arc extinguishing device is used to ensure that the arc generated can be reliably extinguished when the contact is disconnected from the circuit, and the damage of the arc to the contact is reduced. In order to quickly extinguish the arc at the time of disconnection, the contactor is usually equipped with an arc extinguishing device, generally adopting a semi-sealed longitudinal joint ceramic arc extinguishing cover and a strong magnetic blowing circuit.
(5) Other parts: insulated casing, spring, short-circuit ring, transmission mechanism, etc.
Working principle: When the coil is energized, the static iron core generates electromagnetic attraction, and the moving iron core is sucked. Since the contact system is linked with the moving iron core, the moving iron core drives the three dynamic contact pieces to operate at the same time, and the contacts are closed, thereby turning on the power supply. . When the coil is de-energized, the suction force disappears, and the moving iron core linkage part is separated by the reaction force of the spring, so that the main contact is disconnected and the power is cut off.
Principle of selection of AC contactors
The contactor is used as the equipment for switching off the load power supply. The contactor should be selected according to the requirements of the controlled equipment. Except the rated working voltage is the same as the rated working voltage of the controlled equipment, the load power, usage category and control of the controlled equipment. Mode, operating frequency, working life, installation method, installation size and economy are the basis for selection. The selection principles are as follows:
(1) The voltage level of the AC contactor should be the same as the load, and the type of contactor to be used should be compatible with the load.
(2) The calculated current of the load must conform to the capacity level of the contactor, that is, the calculated current is less than or equal to the rated operating current of the contactor. The contact current of the contactor is greater than the starting current of the load. The breaking current is greater than the current required for the breaking of the load. The calculated current of the load should take into account the actual working environment and working conditions. For a load with a long starting time, the peak current of half an hour cannot exceed the convention. Heating current.
(3) According to short-term dynamic and thermal stability check. The three-phase short-circuit current of the line should not exceed the dynamic and thermal stable current allowed by the contactor. When the contactor is used to disconnect the short-circuit current, the breaking capacity of the contactor should also be verified.
(4) The rated voltage, current, auxiliary contact quantity and current capacity of the contactor attracting coil should meet the control circuit wiring requirements. To consider the length of the line connected to the contactor control loop, the recommended operating voltage value, the contactor should be able to work at rated voltage of 85% to 110%. If the line is too long, the contactor coil may not reflect the closing command because the voltage drop is too large; it may not work for the trip command because the line capacitance is too large.
(5) Verify the operating frequency allowed by the contactor based on the number of operations. If the operating frequency exceeds the specified value, the rated current should be doubled.
(6) The short circuit protection component parameters should be selected in conjunction with the contactor parameters.
(7) The installation distance of the contactor and other components must comply with the relevant national standard, and the maintenance and wiring distance should be considered.
(8) Selection of AC contactor under special requirements
1 anti-sway electric AC contactor
The power system slams the power supply system due to lightning strikes, reclosing after a short circuit, and automatic recovery of a single-phase human short-term fault after grounding. The sloshing time is generally less than a few seconds.
In the case of continuous production requirements, the process does not allow the equipment to be interrupted (shake) in the short-term power supply, causing the equipment to trip and power down. A new type of electronic control equipment can be used: FS series anti-sway electric AC contactor.
FS series anti-sway electric contactor does not depend on auxiliary working power supply, does not rely on auxiliary mechanical device, has small volume and high reliability. It adopts powerful suction device, double winding coil, and the contactor has no harmful vibration when it is released by suction, avoiding The arc welding caused by the contact jitter when the grid is out of pressure reduces the contact wear. The contactor coil has an energy storage mechanism. When the sway occurs, the contactor coil is delayed to release, and the auxiliary contact delays the release of the control signal, thereby avoiding the sloshing time, the sway time is caused by the nature of the load and the power is cut off. The length of the contactor is adjustable, and the contactor delay time is adjustable.
2 energy-saving AC contactor
The power saving of the AC contactor refers to the use of various power saving technologies to reduce the active and reactive power consumed when operating the electromagnetic system. The operating electromagnetic system of the AC contactor generally adopts the AC control power supply. The existing AC contactor of 63A or more in China consumes tens of watts to several hundred watts of active power during the holding, and the reactive power is in the tens of Between a few hundred, the power consumed by the core is about 65% to 75%, the short-circuit ring is about 25% to 30%, and the coil is about 3% to 5%, so the AC holding current can be changed to DC. Holding, or using mechanical structure holding, current limiting, etc., can reduce most of the power loss in the short circuit, and can eliminate, reduce noise and improve the environment.
According to the principle, it is generally divided into three categories: power saver, node coil, and power-saving AC contactor. The electromagnetic system adopts a power-saving device, which can make the electromagnetic noise-free and low temperature rise, and solves the problem that the power-saving device has a release delay, such as the domestic CJ40 series.
3 AC contactor with additional functions
The application of electronic technology can easily add main circuit protection functions in the contactor, such as under-voltage, over-voltage protection, phase-fail protection, and leakage protection. In the event of motor burnout, the contactor has a poor contact with one phase, which is 11%. Therefore, it is necessary to select electrical components such as circuit breakers and contactors with phase failure protection.
The contactor plus auxiliary module can meet some special requirements. Adding mechanical interlocking can form reversible contactor, realize positive and negative reversible rotation of motor, or two contactors plus mechanical interlocking to realize electrical interlock of main circuit, can be used for frequency conversion/power frequency switching of frequency converter; gas-filled delay contact and auxiliary The contact group can realize the motor Y/â–³ start; the air delay contact can constitute the delay contactor.
The electromagnetic coil of the AC contactor can be used as the low voltage protection of the motor, and the control loop should be powered by the main circuit of the motor. If the power is supplied by other power sources, the control power should be automatically disconnected when the main circuit loses pressure.
Contactor installation method
(1) Before installing the contactor, check whether the technical data such as the rated voltage of the coil is in accordance with the actual use, and then wipe the iron and rust preventive grease or rust on the iron surface with gasoline to avoid sticking with grease after repeated use. The electric shock cannot be released when the contactor is powered off.
(2) When the contactor is installed, it should be installed vertically, and its inclination should not exceed 5°, otherwise it will affect the operating characteristics of the contactor. When installing a contactor with a heat dissipation hole, the heat dissipation hole should be placed in the up and down position to facilitate heat dissipation of the coil.
(3) When installing and wiring the contactor, be careful not to let the debris fall into the contactor, so as to avoid jamming and burning the coil. At the same time, tighten the screw to prevent the vibration from loosening.
(4) After checking the wiring is correct, the main coil should be energized and divided several times to check whether the product action is reliable before it can be put into use.
(5) For the contactor for reversible conversion, in order to ensure reliable interlocking, in addition to the electric interlock, a mechanical interlocking mechanism should be installed.
Daily use management
(1) Regularly check the power supply voltage of the contactor coil, and prevent the coil from overheating when the voltage is too high. The impact force is large when the magnetic system is closed, and it is easy to damage related parts; if the voltage is too low, the contactor closes slowly and is easy to move. Mechanical jamming, the contacts are easy to sinter together, causing undesirable effects during shifting or commutation, resulting in failure of the automatic control circuit.
(2) Regularly clean and remove dust with high-quality cleaning cloth or brush; if using dry compressed air to blow ash, the air pressure should not exceed O.2MPa, and should be deflated before use, the water vapor in the pipeline And after the dust is blown out and used again, these two points are often neglected and bring about undue trouble.
When conductive dust or putty is adhered to the conductive portion, insulation failure may occur, and even a phase-to-phase short circuit may occur, and the movable mechanical component may be jammed and mechanical wear may be increased.
(3) Regularly check the working surface of the core to remove oil, dust and rust. Because their presence can cause noise and the contactor does not release when the power is turned off, or the release action is delayed.
(4) It is necessary to regularly check the wear condition of moving parts to prevent mechanical wear jams and the like, and the fault range is expanded.
(5) Regularly check whether the fastening connectors are loose, especially when the contact surface of the contactor is subjected to vibration. Due to the looseness of the connecting fastener, the mechanical part is blocked and the wear is increased; and the looseness of the conductive part may cause poor conductive contact, increase the contact resistance, cause overheating, discolor the metal member, and burn the insulating material. The hot spot can be determined intuitively by the discoloration condition of the metal member and the degree of scorch of the insulating member. The pressure drop can also be measured with a millivoltmeter to determine the hot spot. After the overheating is found, the control system should be powered down for processing. Metal parts are best not to be treated with trowels, gold grit, etc., which will shorten the service life. It is recommended to use metallographic sandpaper for treatment. Of course, it should be cleaned after treatment; when repairing the insulation, completely remove the burnt area.
(6) Regularly check the contactor contacts for black soot, metal particles, surface leveling and contact pressure, opening distance and overtravel conditions, to clean the contacts and adjust the contact pressure, opening distance and overtravel. Within the scope. When cleaning the contacts, it is best not to use a trowel to level the contacts to the working surface (working point or line), which will shorten the life of the contacts.
The pressure adjustment should include initial pressure and final pressure adjustment. The initial pressure refers to the pressure acting on the contact when the moving and stationary contacts are in contact; and the final pressure refers to the pressure acting on the contact after the contact is completely closed. The initial pressure measurement is measured when the contact is open; the final pressure is measured when the contact is fully closed. Care should be taken during measurement to make the direction of the tension perpendicular to the contact line. There are many methods of measurement, one of which is to measure the corresponding pressure of the height of the spring installation space when the contact is just separated and completely closed by a spring dynamometer, which are the initial pressure and the final pressure, respectively. The contact opening and overtravel can be measured with calipers, internal calipers and special models. Of course, it is also possible to measure the height change of the contact spring.
For multi-phase rotating contactors with copper contacts, the contacts should be adjusted so that the contacts can be in contact at the same time. If the phases are not in contact, it is generally not more than O.5ram. Also, the position of the contacts should be adjusted to have a certain amount of rolling and sliding during the closing process. The oxide film on the surface of the contact is scratched to reduce the contact resistance. For direct-acting contacts containing silver, avoid the formation of silver oxide, which will shorten the service life. Since silver oxide can decompose silver after being heated, such contact contact resistance is small and stable.
(7) Regularly check whether the contactor coil is firmly attached to the core and the temperature rise changes.
(8) Regularly check the condition of the arc extinguishing chamber to prevent short circuit faults. Due to the opening and closing action of the contactor, black soot and/or metal particles are attached to the arc extinguishing chamber wall and the arc extinguishing grid, so that the arc extinguishing performance is deteriorated, and a short circuit fault is easily generated, so it should be cleaned and arranged. If it is cleaned with solvent, it should be used after drying, otherwise it will cause arc short circuit failure. For the ceramic arc extinguishing chamber and asbestos arc extinguishing chamber, it is brittle and brittle, and special care should be taken not to collide. If it is broken, it should be replaced. After replacing the arc extinguishing chamber, it should be dried before use, and should be replaced with the same type and the same specifications of the arc extinguishing grid; the number of arc extinguishing grid should not be less.
(9) Check the insulation regularly. The insulation resistance to ground in the hot state of the coil in the system shall not be less than 2MΩ. If it is lower than this value, the cause should be ascertained. When the coil is in a cold state, its value must not be less than 0.5 MΩ.
(10) Before power-on operation, check the flexibility of the movable mechanism of the contactor by hand, and inject a proper amount of lubricating oil into the bearing on schedule. When it is found that the moving mechanism has jamming and other inflexibility, it should be put back into use after returning to normal. .
(11) Measure the working current or loss power in the coil when the armature is closed; measure the DC resistance of the coil.
(12) Precautions for contactor replacement.
1 The new contactor under the rated voltage of the control circuit, the loss of the magnetic system and the loss of the conductive part under the working current of the main circuit, can not be much larger than the original contactor, so as to avoid the temperature rise exceeds the specified value.
2 The distance between the contactor and the surrounding metal body in the direction of arcing shall not be less than that specified in the product specification.
3 After the replacement of the contactor, if it is used in the automatic reversible conversion circuit, the operation time when it is reversible conversion should be greater than the arc burning time when the contactor is disconnected to prevent short-circuit failure when the inverter is reversibly converted.
4 After replacement, the rated current and closing and breaking capacity of the contactor should not be lower than the original contactor.
5 Before replacing the contactor, check whether the working voltage of the electromagnetic coil is consistent with the voltage of the control circuit; whether there is looseness of the fastening connector due to transportation and other factors; remove the anti-rust oil on the working surface of the core.