In recent decades, with the development of power electronics technology, microelectronics technology and modern control theory, medium and small power motors have been widely used in industrial and agricultural production and people's daily life. Especially with the rapid development of township enterprises and household appliances, a large number of medium and small power motors are needed. Due to the development and wide application of this kind of motor, its use, maintenance and maintenance work become more and more important. This paper mainly introduces the development and present situation of motor technology, the working principle, operation and maintenance of motor. Key words: technical status quo, working principle, operation and maintenance 1. Development and status quo of motor technology The motor is a machine that works by electromagnetic induction principle. With the development of production, in turn, the development of electric machinery has promoted the continuous improvement of social productivity. Since the end of19th century, the motor has gradually replaced the steam engine as the prime mover to drag the production machinery. For more than a century, although the basic structure of motors has not changed much, the types of motors have increased a lot, and the running performance and economic indicators have also been greatly improved. Moreover, with the development of automatic control system and computer technology, a variety of control motors have been developed on the basis of general rotating motor theory, which has the characteristics of high reliability and good accuracy. There are various classification methods due to different performances. There are two kinds of commonly used motor classification methods: one is divided into four categories: generator, motor, voltage regulator and control motor according to functional purposes. The function of motor is to convert electric energy into mechanical energy, which is used as the power to drive various production machinery. It is the most widely used power machinery and the most important electrical equipment in all sectors of the national economy. The electric energy consumed by various motors accounts for 60%~70% of China's total power generation. Another classification method is based on the structure or speed of the motor, which can be divided into transformer and rotating motor. According to the different power supply current, rotating motors can be divided into DC motors and AC motors. AC motors can be divided into synchronous motors and asynchronous motors. In the process of modern industrial production, in order to realize various production processes, various production machines are needed. Drag all kinds of production machinery to run, pneumatic, hydraulic transmission, electric drag can be. Because electric drive has a series of advantages such as simple control, good adjustment performance, low consumption, economy, remote control and automatic control, most production machines adopt electric drive. According to different types of motors, electric drive systems can be divided into two categories: DC electric drive systems and AC electric drive systems. Throughout the development of electric drive, AC and DC drive modes coexist in various production fields. Before alternating current appeared, DC electric drive was the only electric drive mode. At the end of 0/9 century, AC electric drive was widely used in industry due to the development of economical and practical AC motors. However, with the development of production technology, especially the progress of precision machining and metallurgical industry, new and higher requirements are put forward for the static characteristics and dynamic response of electric drive in starting, braking, forward and reverse rotation, speed regulation accuracy and range. Because AC drive is technically more difficult to meet these requirements than DC drive, DC drive has been used in the technical fields of reversible, speed regulation and high precision drive for quite a period of time since the 20th century, while AC drive is mainly used in constant speed systems. Although the speed regulation performance of DC motor is excellent, the failure rate is high because of the brush and commutator (also known as commutator), and the use environment of the motor is also limited (such as not being used in places with explosive gas and dust), and the development of its voltage grade, rated speed and single machine capacity is also limited. Therefore, after the 1960s, with the development of power electronics technology, the AC speed regulation system of semiconductor AC technology was realized. Especially since 1970s, the development of large-scale integrated circuits and computer control technology has created favorable conditions for the wide application of AC electric drive. Such as cascade speed regulation of AC motor, various types of frequency conversion speed regulation, commutator-less motor speed regulation and so on. , so that AC drive gradually has good technical performance such as wide speed regulation range, high steady-state precision, fast dynamic response and four-quadrant reversible operation, and can be completely comparable to DC electric drive in speed regulation performance. In addition, AC electric drive has the advantages of excellent speed regulation performance and low maintenance cost, so it will be widely used in various industrial electrical automation fields in the future, and will gradually replace DC electric drive and become the mainstream of electric drive. After 100 years of technical development, the theory of the motor itself has basically matured. With the development of electrical technology, the requirements for the conversion, control and effective utilization of electric energy are getting higher and higher. The continuous improvement of the performance of electromagnetic materials and the wide application of power electronics technology have injected new vitality into the development of motors. In the future, the motor will continue to develop in the direction of smaller unit power volume, higher electromechanical energy conversion efficiency and more flexible control. A batch of Big Mac cars and a batch of Luqi cars will be presented to the world at the same time. Second, the working principle of the motor At present, AC motors are commonly used, which are divided into 1 and three-phase asynchronous motors. 2. Single-phase AC motor. The first one is mostly used in industry, and the second one is mostly used in civil appliances. The following three-phase asynchronous motor is taken as an example to introduce its basic working principle. The diagram below shows the schematic diagram of three-phase squirrel-cage asynchronous motor. Symmetric three-phase windings U 1-U2, V 1-V2 and W 1-W2 are embedded in the stator core. A guide rod is placed in the rotor slot, and both ends of the guide rod are short-circuited by short-circuit rings to form a cage-shaped closed winding. Stator three-phase windings can be connected in star or triangle. According to the theoretical analysis of rotating magnetic field, if a symmetrical three-phase voltage is applied to the stator symmetrical three-phase winding, a symmetrical three-phase current will flow and a rotating magnetic field will be formed in the air gap of the motor. The rotating speed of this magnetic field is called synchronous speed. Its relationship with grid frequency f 1 and motor pole number p is as follows: n 1=60 f 1/p The steering is related to the arrangement of three-phase windings and the phase sequence of three-phase current. In the figure, U, V and W phases are arranged clockwise. When the three-phase current of U, V and W phase sequence passes through the stator winding, the rotating magnetic field of the stator rotates clockwise. Because the rotor is stationary, there is relative motion between the rotor and the rotating magnetic field, and the rotor conductor generates induced electromotive force due to cutting the stator magnetic field. Because the rotor winding itself is closed, there is current flowing in the rotor winding. The rotor active current is in phase with the rotor induced electromotive force, and its direction can be determined by the "right-handed generator law". The rotor winding with active component current will produce electromagnetic force F under the action of stator rotating magnetic field, and its direction is determined by the "left-handed motor law". The electromagnetic force forms an electromagnetic torque on the rotating shaft, which acts in the same direction as the rotating magnetic field, dragging the rotor to rotate along the rotating direction of the rotating magnetic field, and converting the input electric energy into rotating mechanical energy. If there is a mechanical load on the motor shaft, the mechanical load rotates with the rotation of the motor, and the motor does work on the mechanical load. From the above analysis, it can be seen that the basic working principle of three-phase asynchronous motor rotation is that (1) three-phase symmetrical winding generates a circular rotating magnetic field through three-phase symmetrical current. (2) the rotor conductor cuts the rotating magnetic field to induce electromotive force and current; (3) The current-carrying conductor of the rotor is acted by the electromagnetic force in the magnetic field to form an electromagnetic torque, which drives the motor rotor to rotate. 3. Operation and maintenance of the motor (1) Preparation before starting the motor In order to ensure the normal and safe starting of the motor, the following preparations should be made before starting: (1) Check whether the power supply is energized and the voltage is normal. If the power supply voltage is too high or too low, it is not suitable for starting. (2) Whether the starter is normal, such as whether the parts are in good condition, whether it is flexible to use, whether the contacts are in good condition, whether the wiring is correct and firm, etc. (3) whether the fuse size is appropriate, whether the installation is firm, and whether it is blown or damaged. (4) The joints on the motor terminal board are not loose or oxidized. (5) Check the transmission device, such as whether the belt is tight, whether the connection is firm, and whether the screws and pins of the coupling are fastened. (6) Drive the rotor of the motor and the shaft of the loader to see if it can rotate flexibly. (7) Check whether the motor and starter shell are grounded, whether the grounding wire is open, whether the grounding screw is loose or falling off, etc. (8) Remove sundries around the motor, and remove dust and grease on the surface of the frame. (9) Check whether the loaded machine is ready for starting. (10) If the wound motor is in normal operation, always observe whether the motor slip ring has eccentric swing; Observe whether the spark of slip ring is abnormal. Whether the carbon brush on the slip ring should be replaced. (2) Problems that should be paid attention to when starting (1) After turning on the power supply, if the motor does not turn, immediately cut off the power supply, do not hesitate to wait, and do not turn on the power to check whether the motor is out of order, otherwise it will burn out the motor and cause danger. (2) When starting, pay attention to the working conditions of motor, transmission device and load machinery, as well as the instructions of ammeter and voltmeter on the line. If there is any abnormality, cut off the power supply immediately for inspection, and then start the line after troubleshooting. (3) When starting the motor with manual compensator or manual star delta starter, special attention should be paid to the operation sequence. Be sure to push the handle to the start position first, and then pull it to the running position after the motor speed is stable to prevent equipment and personal accidents caused by misoperation. (4) The motors on the same line should not be started at the same time. Generally, it should be started one by one from big to small to avoid too many motors starting at the same time and too much current on the line. Too large voltage drop makes it difficult to start the motor, resulting in line failure or switch equipment tripping. (5) When starting, if the rotation direction of the motor is reversed, the power supply should be cut off immediately, and the position of any two phases in the three-phase power line can be changed. (3) Monitoring the motor in operation When the motor is running, the personnel on duty can monitor its operation through instruments and sensory organs, so as to find problems early and reduce or avoid failures. 1. Monitor the temperature of the motor. During normal operation, the motor will generate heat, which will increase the temperature of the motor, but it should not exceed the allowable limit. If the motor load is too large, the operating environment temperature is too high, the ventilation is not smooth or there is a fault in operation, its temperature will exceed the allowable limit, resulting in overheating and burning of the winding. Therefore, the temperature of the motor is the main sign reflecting the operation of the motor, and it should be checked frequently during operation. To judge whether the motor is overheated, the following methods can be used: (1) Touch by hand: If the shell is touched by hand, the motor temperature is normal; If you put your hand on it, it will burn back immediately, indicating that the motor is overheated. (2) Drop 2~3 drops of water on the motor housing. If there is only hot air and no sound, the motor is not overheated. If the water droplets evaporate rapidly with hissing, the motor will overheat. (3) The accurate way to judge whether the motor is overheated is to measure it with a thermometer. If the motor is found to be overheated, it should be stopped immediately for inspection, and then used after the cause is found out and the fault is eliminated. 2. Monitoring the current of the motor Generally, the motor with large capacity should be equipped with an ammeter to monitor its current at any time. If the current magnitude or three-phase current imbalance exceeds the allowable value. Stop the car immediately for inspection. Generally, motors with small capacity are not equipped with ammeters, but they are often measured with clamp meters. 3. It is best to install a voltmeter and a transfer switch on the power supply of the motor to monitor its three-phase power supply and voltage. Too high, too low or unbalanced three-phase voltage of motor power supply, especially the lack of three-phase power supply, will bring bad consequences. If this situation is found, stop the car immediately, find out the reason and troubleshoot before using it. 4. Pay attention to the vibration, noise and smell of the motor. When the motor is running normally, it should be smooth and light, without abnormal smell and noise. If there is severe vibration, noise and burning smell, stop for inspection and repair. 5. Pay attention to check the transmission device. When the motor is running, always check whether the pulley or coupling is loose and whether the drive belt is too tight or too loose. If so, stop and tighten it or adjust it. 6. Pay attention to the working condition of the bearing. When the motor is running, pay attention to the bearing sound and heat. If the bearing sounds abnormal or overheated, check whether the lubrication condition is good and whether there is wear. 7. Pay attention to the slip ring of AC motor or commutator of DC motor. In the operation of spark motor, sparks will inevitably appear between brush and commutator or slip ring. If the spark is greater than a certain limit, especially when there is a red discharge arc spark, it will have a destructive impact and must be corrected in time. (IV) Regular inspection and maintenance of the motor In order to ensure the normal operation of the motor, in addition to the correct use in accordance with the operating procedures, regular inspection and maintenance should be carried out, and attention should be paid to monitoring and maintenance during operation. The interval time can be determined according to the type of motor and the use environment. The main inspection and maintenance items are as follows: (1) Remove the dust and sludge outside the motor base in time. If there is a lot of dust in the use environment, it is best to clean it every day. (2) Always check whether the wiring board screws are loose or burned. (3) Measure the insulation resistance of the motor regularly, especially in the humid environment. (4) Regularly clean the bearing with kerosene and replace it with new oil (generally once every six months). When changing oil, it is not advisable to fill it up, which generally accounts for 1/2~ 1/3 of the oil chamber. Otherwise, it is easy to generate heat or throw it out. Oil should be added from one side, and impurities that are not cleaned can be squeezed out from the other side. (5) Check the startup equipment regularly to see whether the contacts and wiring are burnt or oxidized and whether the contact is good. (6) Insulation inspection. The insulating ability of insulating materials varies with the degree of dryness, so it is very important to keep the motor winding dry. The wet working environment and corrosive gas in the workshop will destroy the insulation of the motor. The most common fault is winding grounding fault, that is, insulation damage, which makes the charged part collide with the metal part that should not be charged, such as bushing. This kind of fault not only affects the normal operation of the motor. It will also endanger personal safety. Therefore, when the motor is in use, always check the insulation resistance, and also pay attention to check whether the grounding of the motor shell is reliable. (7) In addition to regular maintenance according to the above items, the motor should be overhauled after running for one year. The purpose of overhaul is to thoroughly and comprehensively inspect and maintain the motor, supplement the missing and worn parts of the motor, thoroughly remove the dust and dirt inside and outside the motor, check the insulation, clean the bearing and check its wear. Conclusion Electric motors play an important role in China's economic construction. With China's entry into WTO, China's automobile industry is facing increasingly fierce competition pressure and challenges from the international community. Starting from energy conservation and environmental protection, high-efficiency motors are the current international development trend. In this way, it is very necessary to promote high-efficiency motors in China. However, how to maintain it in daily use is evident. This paper focuses on the technical development and present situation, working principle, operation and maintenance of the motor, hoping to help people who are or will be engaged in motor work. Five. References (this article comes from 1 or so: Liu Shurong, Zhang Yunbo Higher Education Press 2: Paula Tsui Higher Education Press 3: Yang Lisun Jin Fan Cui Xiang [Motor Use and Maintenance].