Contactor is a widely used switching appliance, which uses electromagnetic, pneumatic or hydraulic principles to control the circuit to achieve the main circuit on-off.The contactor has the advantages of strong current breaking ability, rapid action, safe operation, frequent operation and remote control, but it can not cut off the short circuit current, so the contactor usually must be connected withFuseUsed together.The main control objects of the contactor areMotor, can also control other powerload, such asElectric welding machine、electric furnaceEtc.[6]
There are many classification methods for contactors, which can be divided into electromagnetic contactors, pneumatic contactors and hydraulic contactors according to the different power sources of the drive contact system;It can also be divided into air contactor, oil immersed contactor and vacuum contactor according to the nature of arc extinguishing medium.[6]
The working principle of the contactor is: when the contactor coil is energized,coilThe current will generate a magnetic field, which will make the static iron core generate electromagnetic attraction to attract the moving iron core, and drive the AC contactor point action. The normally closed contact will open, and the normally open contact will close. The two are linked.When the coil is powered off, the electromagnetic force disappears, and the armature is released under the action of the release spring, making the contact recover. The normally open contact is disconnected, and the normally closed contact is closed.DC contactorIts working principle is a little similar to that of temperature switch.
Device function
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Contactor[4]
In electrotechnics, because the contactor is a device that can quickly cut off the AC and DC main circuits and can frequently turn on and off the large current control circuit (up to 800A), it is often used as a control object for motors, and can also be used to control power loads such as factory equipment, electric heaters, machine tools and various power units. The contactor can not only turn on and turn off the circuit,It also has the function of low-voltage release protection.The contactor has large control capacity and is suitable for frequent operation and remote controlautomatic control systemOne of the important components in.
As a high-power switching device, contactor is widely used in aerospace, aviation, weapons, ships, electronics and other system equipment. Its load current is greater than 25A and voltage is 25VDC;115VAC、402Hz；386VAC, 50Hz, mainly used as power distribution switch in equipment to control power supply or start/stop control of high-power motor, is a key device in equipment and plays an important role.[3]In industrial electrical industry, there are many types of contactors, and the working current varies from 5A-1000A, so they are widely used.
Main structure
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AC contactorThe main contact is used to control the circuit, and the auxiliary contact is used to conduct the control circuit.
The main contact is normally open, while the auxiliary contact usually has two pairs of normally open contacts and normally closed contacts. Small contactors are also often used asIntermediate relayCooperate with the main circuit.
The contact of AC contactor is made of silver tungsten alloy, which has good conductivity and high temperature ablation resistance.
Contactor[5]
The power for the action of AC contactor comes from the magnetic field generated by AC through the coil with iron core,electromagnetThe core is composed of two "mountain" shaped young silicon steel sheets, one of which is a fixed core, and is covered with coils. The working voltage can be selected in a variety of ways.In order to stabilize the magnetic force, a short circuit ring is added to the pull in surface of the iron core.After the AC contactor loses power, it returns by spring.
The other half is a movable iron core with the same structure as the fixed iron core to drive the main contact and auxiliary contact to be closed and disconnected.
Contactors above 20A are equipped with arc extinguishing hoods. The electromagnetic force generated when the circuit is disconnected is used to quickly break the arc and protect the contacts.
The contactor can be operated at a high frequency. When it is used as power on and off control, the maximum operating frequency can reach 1200 times per hour.
The service life of the contactor is very high, the mechanical life is usually millions to 10 million times, and the electrical life is generally hundreds of thousands to millions of times.
technological development
The AC contactor is made as a whole, and its shape and performance are also improving, but its function remains unchanged.No matter to what extent the technology develops, ordinary AC contactors still have an important position.
Air type electromagnetic contactor(English: Magnetic Contact): mainly composed of contact system, electromagnetic operating system, support, auxiliary contact and shell (or chassis).
Because of communicationElectromagnetic contactorThe coil of the electromagnetic contactor is usually powered by AC power supply. After the contactor is energized, there is usually a high decibel "cluck" noise, which is also the feature of the electromagnetic contactor.
After the 1980s, various countries studied the soundless and power saving of AC contactor electromagnets. One of the basic feasible schemes is to reduce the voltage of AC power supply with transformer, and thenrectifierIntoDC power supplyRear power supply, but this complex control mode is rare.
Vacuum contactor：vacuumThe contactor is a contactor whose contact system adopts vacuum degaussing chamber.
Semiconductor contactor: Semiconductor contactor is a contactor that completes current operation by changing the conduction state and open circuit state of circuit circuit.
Permanent magnet contactorThe permanent magnet AC contactor is a kind of low-power contactor formed by replacing the traditional electromagnet driving mechanism with a permanent magnet driving mechanism based on the principle that the same polarity repels and the different polarity attracts.
Main categories
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It can be divided into:DC contactor, AC contactor.
It is divided into:Electromagnetic contactorPermanent magnet contactor。
Permanent magnet AC contactor is a kind of low-power contactor, which uses the same-sex repulsion of magnetic poles and replaces the traditional electromagnet drive mechanism with a permanent magnet drive mechanism.Domestic mature product models: CJ20JNSFC1、NSFC2、NSFC3、NSFC4、NSFC5、NSFC12、NSFC19、CJ40J、NSFMR。
DC contactor
Development Status of DC Contactors at Home and Abroad
The overall development trend of contactors will be towards the direction of long electrical life, high reliability, multi-function, environmental protection, multi specification, intelligence and communication.
Hybrid DC contactor
Compared with the AC current, there is no periodic zero crossing of the current value. Therefore, when the traditional contactor breaks the circuit, the arc between the contacts is strong and the arcing time is long, so as to fully release the remaining energy in the circuit.The burning of the arc produces high temperature and strong light, which has a serious ablation effect on the contact surface. The contact material is gradually lost after several interruptions. When the contact is severely worn, the DC contactor is scrapped and the circuit cannot be disconnected.[1]
With the rapid development of power electronic technology, people apply power electronic components to DC contactors and ingeniously create a hybrid DC contactor, which makes DC contactors stride forward to a new step towards intelligence and controllability.This hybrid contactor takes advantage of the advantages of small contact resistance and small conduction voltage drop of the traditional DC contactor in the closed conduction state, and is composed of reverse parallel thyristors and control module unitsContactless switchIt is connected in parallel to the contact of traditional DC contactor.This contactless power electronic switch does not produce arc when breaking the circuit, which avoids the arc pair in traditional contactorscontact material The service life and reliability of the contact are greatly increased due to the electrical wear of the contact.[1]
Permanent magnet mechanism of DC contactor
As one of the widely used electrical switches, the DC contactor has a huge number of production and demand. In the normal use process, the electromagnet coil has been working with electricity, generating electromagnetic attraction, ensuring that the iron core and armature are engaged, with moving and static contacts closed, and the circuit is connected.In the above process, the coil itself has resistance and continuously consumes electric energy, which is one of the main use costs of the DC contactor and wastes a lot of energy and property. Therefore, how to reduce the working energy consumption of the DC contactor is the key and difficult point to study the DC contactor.The permanent magnet operating mechanism of DC contactor is aElectromagnetic operating mechanismThe hybrid operating mechanism, which combines the electromagnetic operating mechanism with the permanent magnet, not only uses the original electromagnetic attraction and spring reaction force as the power for the iron core to pull in and separate, but also adds the attraction of the permanent magnet to the iron core. It uses the energy storage capacitor to charge and discharge electricity to provide closing and opening power, which is commonly referred to as "electromagnetic operation, permanent magnet retention, electronic control"。In the process of opening and closing movement, the electromagnetic force, permanent magnetic force and spring force work together. In the process of stable operation, the permanent magnetic force is used to replace the previous electromagnetic force to keep the armature and core in the closed state.One is permanent magnetOperating mechanismThe electric energy consumption of the holding coil is greatly saved, which is environmentally friendly and energy-saving.On the other hand, compared with electromagnetic actuation, permanent magnet retention actuation has low noise and no pollution.Third, the permanent magnetic actuator eliminates a series of complicated and cumbersome locking protection devices in the electromagnetic mechanism, greatly improving the working reliability of the contactor operating mechanism, reducing the production process and cost, and reducing the volume of the contactor.[1]
Technical status
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Current Status of Contactor Electrical Performance Testing Technology
The research on dynamic detection technology of contactors and other contactors mainly focuses on the following aspects:
1. The computer is used as the upper computer, and A/D sampling plate or DSP is used as the automatic detection system of contact parameters of the lower computer
The self-developed computer detection and control device for electrical life of relay is used to collect overvoltage signals at the beginning, middle and end of the electrical life test of relay.Adopt self-developed A/D sampling plate or high-speed with DSP as the coredata acquisition cardThe contact electrical parameters such as contact voltage drop, voltage between disconnected contacts, main circuit current, etc. are sampled.The control part adopts digital I/O board to controlSolid state relayTo drive the contactor or relay on and off.The software uses VB programming, interrupt processing program to achieve data sampling, logic control and other functions.The data processing in the literature mainly focuses on the calculation of power grid frequency and power factor.Through the analysis of the collected voltage signalfast Fourier transform The time-domain signal is transformed into the frequency-domain signal, and the transformation results are respectively placed in the array of the real part and the imaginary part. The position where the peak occurs is the power grid frequency, and the power grid frequency is calculated using the formula.Fourier transform the collected data, transform the time-domain signal into the frequency-domain signal, calculate the phase of voltage and current, and then calculate the power factor.[2]
2. Relay parameter detection technology based on MCU control technology
With the continuous improvement of the automatic level of electrical apparatus detection, single-chip computers are increasingly applied to the detection and control of various electrical appliances.By improving the traditional experimental device for making and breaking AC contactors, the SCM is used as the control module of the experimental device to control the making and breaking of AC contactorsCurrent transformerData acquisition card and PC are completed.The device can realize real-time data acquisition of contact voltage, current and other dynamic waveforms during the making and breaking process of the contactor. Compared with traditional oscilloscope detection, the contact arc voltage waveform is recorded accurately.Visual C++6.0 software is used to develop the acquisition program and human-computer interface. The data processing program can automatically process the data in real time, reducing the error caused by manual processing of waveform data.The test scheme is simple and feasible, and can realize the analysis of contact voltage and current waveform in the dynamic process of making and breaking of AC contactor.The relay electrical parameter testing device developed by Zhang Qiang and others in the literature takes the enhanced 89C51 single chip microcomputer as the core, and configures AC and DC voltage sources and contact detection circuits to test the action time, action voltage, contact resistance and other electrical parameters of various types of AC and DC voltage relays.In the test of action time, connect the normally closed contact of the tested relay to the high level and the normally open contact to the ground, start the timer to start timing while detecting the rated voltage of the coil, and build a contact level detection circuit to monitor the change of the contact level in real time.Determine the contact action state according to the change of contact level.When the level changes from high to low, stop timing immediately, and then you can read the timing of the timer, which is the corresponding pull in time.Similarly, the release time of the relay can be obtained.At the same time, the test device can also monitor the contact resistance of contacts.The device has a high cost performance ratio, which has a very important reference value for the development of the test device in this topic.[2]
3. Application of virtual instrument technology in parameter detection of switching apparatus
With the development and maturity of virtual instrument technology, virtual instrument technology is more and more used in the testing of relays, contactors and other switching appliances.Virtual instrument technology is a new measurement technology centered on software, which can greatly reduce the cost of test instruments.The measurement function is mainly realized by software programming. With the support of the hardware platform composed of industrial personal computer as the core, the test function of the instrument is realized by programming on the Lab VIEW software development platform.The Lab VIEW application library has loaded many test and control modules for different purposes. Users can directly call relevant modules under the Lab VIEW application program to realize various test functions.Compared with traditional assembly, VB, VC and other text programming languages, Lab VIEW software program is very simple.After installing the driver of the data acquisition card in the Lab VIEW environment, you can call the function function of the card to control the card, collect, process and display data.[2]
4. Acquisition method of relay time parameters
The detection of relay time parameters mainly uses electric stopwatch andLight oscilloscopeThe traditional detection method is slow in measuring speed, large in error and inaccurate in measurement.With the development of computer technology, more and more relay detection devices use microprocessors, and their principles are basically the same.A time parameter detection circuit is mentioned in the literature. The main component of this circuit is a single chip microcomputer. Its detection principle is: when the relay contact is closed, the corresponding input channel voltage of the single chip microcomputer is 5V, and the port is "1". When the relay is disconnected, the corresponding voltage is 0V,I/O portIs "0".When the excitation voltage is applied to the relay, the MCU reads the corresponding digital I/O port of the MCU with a small enough sampling period, and then calculates the corresponding time parameters after data processing.But this method is used to connect the relayDC loadWhen the relay is disconnected, the instantaneous value of the MCU port voltage may also be very small or close to zero because the AC voltage is alternating when the relay is connected to the AC load.Therefore, when the circuit to which the contacts are connected is an AC circuit, using the instantaneous value of the voltage between the contacts to judge the closing and opening state of the contacts, the error will be large, and the accurate value will not be obtained.A computer detection method of relay time parameters is mentioned in the literature. It uses a self-developed acquisition board, which is mainly composed of a single chip computer and its peripheral circuits.This method can detect time parameters such as relay action time, action bounce time, release time, release bounce time, etc.The MCU is connected to the coil drive circuit to control the energization and power-off of the excitation coil, collect the state of the contact when the relay is closed and disconnected, and calculate its time parameters.The detection principle is: when the relay coil is powered on, the contact can be closed after a fixed action time, so the MCU first collects the data 0, and then collects the data 1 after the contact is closed stably.During this process, the contact will bounce and finally reach a stable state. During this period, the data collected by the MCU is either 0 or 1.Set the sampling period of the single chip microcomputer as 0.01ms, and the address value of the data collected by the single chip microcomputer multiplied by the sampling period is the required action time.[2]
5. Contactor dynamic performance testing technology and comprehensive evaluation method
The technical performance of electrical appliances is mainly assessed byType testThis method focuses on the mechanical and electrical life of electrical appliances, and cannot comprehensively evaluate the dynamic characteristics of electrical appliances and the impact of their mechanical and electrical life.Therefore, the research on the comprehensive evaluation of electrical performance based on dynamic characteristics detection has practical guiding significance for the development and delivery inspection of electrical products.By testing the dynamic process of AC contactors, the literature extracts the parameters that can characterize the mechanical and electrical characteristics of contactors from the contact test waveform, and establishes a comprehensive evaluation model of contactor performance, thus forming a comprehensive evaluation system of contactor dynamic performance.The AC contactor dynamic testing device takes DSP as the core, builds various signal sensors, and communicates with the host computer through RS232.The test device can measure the electrical parameters of the contactor excitation current, voltage and coil power consumption in the pull in process.It has a practical guiding role for the construction of the test device in this topic, and its proposed contactor performance evaluation system has an important reference value for the contactor performance degradation and reliability estimation to be studied in this topic.[2]
development direction
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one
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Development of miniaturization and lightweight: Miniaturization and lightweight have always been the basic requirements of contactors. With the development of equipment, the requirements for miniaturization and lightweight become more and more important. Especially for aviation and unmanned equipment, the small size and light weight of contactors are the primary indicators for use and selection.
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Intelligent development: The contactor of traditional structure type only has the function of electrical disconnection, and the load current, voltage detection, overcurrent, overvoltage protection, short circuit protection and other functions are completed by the user on the whole machine.With the development of equipment miniaturization, these functions must be integrated to reduce the equipment volume. Therefore, these protection functions should be integrated with the contactor and completed by the contactor, so as to effectively reduce the overall volume and achieve the goal of equipment miniaturization.In the future, contactors must be developed in the direction of intelligence, that is, in addition to the basic load breaking function, they should also have load current, voltage detection and overcurrent, overvoltage protection, load short circuit protection, 2t inverse time limit protection, bus control and other functions.
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The breaking load voltage is developing towards DC high voltage: The breaking voltage and current of the contactor with traditional structure are generally 25VDC, 1200A;115VAC、400Hz、422A；386VAC, 54Hz, 100A, low voltage, large current range.With the application of equipment system voltage in the direction of high voltage DC, new requirements are put forward for the contactors of the distribution system. It is required that 274VDC series (including 400VDC, 500VDC, 600VDC) DC voltage can be cut off. We call it "high voltage contactor".With the development of new energy and unmanned equipment, high-voltage DC system voltage will be widely used. Contactors used for power distribution control must meet the equipment requirements. Therefore, disconnecting higher DC voltage loads by contactors is the future development direction.
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Long life development：（1）Life requirements under low pressure: The load voltage for contactor disconnection is 28VDC;n5VAC、402Hz；382VAC、50Hz,We call it low-voltage load. The service life of products generally does not exceed 50202 times, and some even less than 2022 times. This can meet the service life requirements in the previous weapons and equipment, but now with the improvement of equipment requirements, the service life requirements in some application fields can no longer be met. Especially in the weapons industry, the service life of equipment is required. Therefore, the service life of contactors needs to be greatly improved.（2）Life requirements under high pressure: The materials in the vacuum chamber will increase the pressure in the vacuum chamber through atomic or molecular exhaust. In order to ensure the proper electrical strength and current breaking capacity of the contactor, the vacuum degree and the total pressure level of the residual gas in the vacuum chamber shall not exceed 12-3hPa.To ensure the lifetime sealing characteristics of more than 39 years, the pressure level should be controlled below 12-7hPa.Therefore, the vacuum degree holding time of the vacuum chamber should meet the service time requirements of weapons and equipment.
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Development of waterproof and sand dust preventionWith the development of unmanned equipment, it is required that the contactors used for power distribution and control should meet the requirements of harsh environment adaptation, such as underwater work, long-term work in harsh dust environment, etc.The contactor of traditional structure type is generally of closed structure, which cannot be waterproof, nor can it work in the harsh dust environment for a long time. Therefore, the contactor is required to meet the waterproof sealing requirements, which also meet the requirements of dust prevention.However, the sealing structure is an adverse factor for the heat dissipation of the contactor itself, which has an impact on its load capacity and life, and needs to be fully considered.
