"Introduction
Rotating machinery refers to machinery that mainly relies on rotating action to complete specific functions, such as steam turbine, gas turbine, water turbine, motor, generator and aeroengine. Motor is the main equipment driving rotating machinery such as fan, water pump and compressor. The power consumption of motor accounts for more than 70% of the total industrial power consumption. It is the largest type of equipment in rotating machinery. Small and medium-sized motors cover the power range of 0.55kw ~ 5000kW, the voltage range of 380V ~ 10kV, and the base number range of H80 ~ H630, At present, there are more than 300 series and more than 1500 varieties of small and medium-sized motor products in China. The annual production accounts for 60% ~ 70% of the annual output of the whole motor. They are widely used in various fields of the national economy such as industry, agriculture, commerce, transportation and national defense. The safe and reliable operation of small and medium-sized motors is of great importance.
As the main driving equipment of various rotating machinery, motor is widely used in various fields of industrial production. A large equipment or a production line often needs dozens or even hundreds of driving and control motors. Even if only one motor fails, it will lead to the failure of the whole equipment, system or production line; However, modern mass production emphasizes continuity and requires complete sets of equipment to operate reliably and continuously. Due to the interruption of equipment operation, even for only a few hours, the loss can be as high as hundreds of thousands, millions or even more, which may seriously lead to the scrapping of complete sets of equipment. Therefore, it is very important for the supporting motor to operate safely and reliably. This paper detects the sensitive parameters of various motors in normal operation, points out the abnormal phenomena, and puts forward a series of methods and steps for diagnosis, so as to help the motor user find the problems earlier and solve the problems faster; In order to avoid the problem expansion caused by various minor faults not found in time, resulting in equipment shutdown or even damage.
1 main phenomena of motor failure
As an electrical equipment that can convert electrical energy into mechanical energy for use, motor is widely used in industry and household fields. The structure is relatively simple, which is composed of two main parts: stator and rotor, as well as end cover, bearing, fan and other auxiliary parts. During the operation of the motor, these parts may have problems, some are improper process or design in the manufacturing process, some are strain or improper use in the use process. These problems will cause all kinds of abnormal phenomena. Taken together, there are the following kinds of phenomena: abnormal temperature, abnormal vibration and noise, abnormal electrical parameters, etc.
2 fault phenomenon and mechanism of various motors
2.1 abnormal temperature 2.1.1 overview the main heating components of the motor are generally windings and bearings. Specific temperature abnormalities on the surface are generally divided into the following categories: too high bearing temperature, too high winding temperature and too high casing temperature. 2.1.2 the bearing temperature is too high 2.1.2.1 the bearing temperature is too high, which will harm the motor bearing. As the main component supporting the rotor, if the temperature is too high and is not solved, it will lead to the loss of motor bearing and low efficiency; It may even cause the motor bearing to bite, causing the motor to stall suddenly; Finally, the whole traditional system was damaged. Therefore, the monitoring of motor bearing condition is very important. 2.1.2.2 the causes of high bearing temperature generally include the following types of wear: mechanical parts will inevitably lose in the long-term operation process, and the bearing should be replaced every few years for the motor in normal operation. Slack in this aspect may cause excessive wear of the bearing.
After excessive wear, the bearing will produce a series of phenomena, such as high bearing temperature, large bearing vibration and abnormal bearing noise. Lack of oil: lubricating grease will be added to the bearing of the motor to lubricate the bearing. The lubricating grease in the bearing of the motor in normal operation will be gradually lost. When the loss of lubricating grease is too large, it will cause poor lubrication and a significant increase in the temperature of the motor bearing. When it is found that the bearing temperature is too high without other accompanying phenomena, the motor shall be shut down to check the bearing condition of the motor. Others: as an integral part of the motor, if the temperature of each part is too high, it may be transmitted to the bearing, resulting in too high bearing temperature. Therefore, when the bearing is found to be normal, focus on the abnormal conditions of each part of the motor near the problem bearing.
The problem of significant increase in bearing temperature needs to be investigated in time, because if such problems are not solved in time, when the bearing temperature is too high, it may cause grease evaporation and other phenomena, which will greatly increase the loss of grease and cause bearing damage or even bite in a very short time. Therefore, when the bearing temperature is too high, it needs to be investigated in time to avoid further harm. 2.1.3 the harm of too high winding temperature 2.1.3.1 as the most important part of converting electrical energy into mechanical energy, the state monitoring of motor winding is very important. Through the monitoring of winding temperature, many problems can be reflected, such as excessive load caused by bearing problems, damaged winding insulation, abnormal load end, etc., which will lead to too high winding temperature of motor.
Too high temperature will damage the insulation of the winding, and conduction to the bearing will accelerate the loss of bearing grease; Therefore, the monitoring of winding temperature is also very important. 2.1.3.2 reasons for excessive winding temperature generally include the following categories: abnormal load: before purchasing the motor, the user of the motor will select a suitable motor according to the actual use. The sudden change of load during operation will lead to obvious change in the winding temperature of the motor. Sudden changes in general load will also lead to sudden changes in motor current.
Abnormal heat dissipation: during the operation of the motor, various losses will occur, including stator / rotor loss and iron loss, which are mainly reflected in the winding temperature. Therefore, this part of heat needs to be dissipated by components such as heat dissipation ribs on the casing. When it is found that the winding temperature is too high, check whether there is dirt blocking at the air inlet or outlet of the motor, Check whether the cooling rib is damaged. Winding aging: the internal temperature of the motor in normal operation is generally high. For the motor powered by the frequency converter, there are also harmonic problems. These problems will lead to the aging of windings, magnetic steel and other components. When the aging reaches a certain degree, the performance of the motor will decline. When the motor changes from normal operation to overload operation, the temperature of the winding will rise significantly, Generally, the winding temperature change caused by such problems is relatively slow, and it is not easy to have a sudden rise in temperature.
The excessive temperature of the winding is a relatively slow abnormal phenomenon compared with the temperature of the motor bearing. Generally, the excessive temperature of the winding will be accompanied by various other abnormalities, but the temperature monitoring of the winding is relatively simple compared with the monitoring of other values (such as vibration abnormalities caused by fan damage), Therefore, the monitoring of winding temperature is the most common method for motor condition detection. 2.1.4 casing temperature is too high 2.1.4.1 importance of casing temperature monitoring for large motors, the method of embedding temperature monitoring equipment is generally used to monitor the bearings or windings of motors, but for small motors, the method of embedding temperature monitoring equipment is sometimes difficult to achieve. Similarly, some motors do not embed temperature monitoring probes when leaving the factory, The non-contact temperature measurement method can be adopted, and the professional personnel on duty patrol the motor to replace the embedded temperature monitoring probe.
Similarly, it can play an early warning role for excessive temperature. 2.1.5 it can be seen from the above that in the actual use of the motor, many faults will lead to abnormal temperature. Therefore, temperature monitoring is very important in the actual use of the motor. For this, the national standard GB 14711 specifies the temperature of the main parts of the motor in safe use, which is combed in the following table, as shown in Table 1. Table 1 temperature (℃) and temperature rise (k) limits of main parts of traditional motor
2.2 abnormal noise and vibration 2.2.1 overview as an electrical equipment that converts electrical energy into mechanical energy, the motor will inevitably produce noise and vibration in the process of use, especially when the mechanical structure of the motor is abnormal, the first abnormal phenomenon is the significant increase of noise or vibration. Therefore, the monitoring of noise and vibration can give early warning of motor failure, so as not to cause greater harm. 2.2.2 excessive vibration 2.2.2.1 excessive vibration endangers the motor in normal operation and will inevitably produce vibration. Vibration, as an important technical index of the motor, is also one of the main items for type test of various motors. The motor in long-term operation will produce obvious vibration when mechanical parts are loose, For example, excessive bearing wear will lead to greater vibration on the extension side of the motor shaft. The greater vibration is a vicious cycle process. Excessive vibration will cause damage to more parts, resulting in greater vibration, and finally cause serious hazards such as shaft breakage and foot breakage, which may lead to serious accidents of "machine destruction and human death".
2.2.2.2 there are many reasons for excessive vibration, including damage to mechanical structure, aging of electrical structure and installation itself. From the perspective of monitoring, it is divided into vibration value abnormalities at various parts, mainly including front end cover vibration abnormalities, rear end cover vibration abnormalities and base vibration abnormalities. Abnormal vibration of the front end cover: for long-term operation of the motor, the bearing is the most aging mechanical component. When the bearing outlet is worn, the obvious vibration on the end cover side of the motor may increase. In addition, the problem of the motor output shaft may also cause abnormal vibration on the end cover side. When the motor has process problems or improper use in the manufacturing process, After long-term operation, it may cause cracks or bending deformation of the motor shaft, resulting in uneven stress of the motor. The vibration caused by such problems is often obvious; When this kind of problem occurs, radial runout is often visible to the naked eye on the output shaft side of the motor.
Abnormal vibration of rear end cover: most motors are equipped with fans for heat dissipation on the non shaft side. When the fan is damaged, the vibration on the rear end cover side of the motor will obviously increase. For such problems, you can stop the machine and check the integrity of the fan. If the fan is in good condition, you should check whether the rear bearing of the motor is abnormal. Abnormal base vibration: as the main body of the motor, all kinds of vibration will be transmitted to the base of the motor. When it is found that the overall vibration of the motor becomes larger, first confirm whether the installation of the motor is loose and ensure whether each installation fastener is loose or deformed; When the fastening parts installed outside the motor and all fastening parts of the motor body are not loose, the machine shall be disassembled for inspection to confirm whether the internal components of the motor are loose, such as the looseness of rotor eccentric block, rotor chamber sweeping, etc. 2.2.2.3 vibration limit of traditional motor there are many factors causing vibration. In terms of detection and monitoring, it is mainly to monitor the displacement, speed and acceleration of the motor in three directions, so as to analyze the possible problems of a certain part of the motor. The following table combs the vibration limit of traditional motor during operation, as shown in Table 2. Table 2 vibration limits of traditional motors
2.2.3 excessive noise 2.2.3.1 excessive noise is harmful. The noise generated by the motor is mainly divided into mechanical noise and electromagnetic noise. These two types of noise will be found for the motor in normal operation. Compared with the abnormal vibration of the motor, the sharp increase of noise is easier to be found and detected, and also easier to attract attention. Therefore, abnormal noise is the most easily found abnormal phenomenon. Excessive electromagnetic noise means that there may be problems in the motor winding coil, while excessive mechanical noise means that there may be looseness or even fracture of mechanical parts. Therefore, when abnormal noise is found from the running motor, the problem shall be investigated in time, and the machine shall be shut down immediately if it is serious, so as to avoid more serious noise accidents. 2.2.3.2 the causes of excessive noise are sometimes difficult to distinguish between electromagnetic noise and mechanical noise. At this time, the method of shutdown detection can be used for diagnosis. When the motor power is disconnected, the motor speed decreases slowly. At this time, if the noise still exists, it is mechanical noise. If the noise disappears immediately, it is generally electromagnetic noise.
2.2.3.2.1 the cause of excessive electromagnetic noise is generally caused by high-frequency vibration of winding and other components due to large harmonic in the current connected to the winding. Generally, it is obvious on the motor powered by the frequency converter. When the power quality of the frequency converter is poor, the long-term operation will damage the winding insulation of the motor and cause more obvious electromagnetic noise; In addition, the rotor air gap caused by the casting process and the looseness of the winding will increase the electromagnetic noise of the motor. Since the electromagnetic noise is generally generated by the internal electrical energized parts of the motor, the diagnosis is generally complex. Therefore, when troubleshooting, generally first investigate the external causes such as power quality problems, and then disassemble the motor to troubleshoot the internal problems.
2.2.3.2.2 causes of excessive mechanical noise rotating motor, as a high-speed rotating electrical equipment, will inevitably produce vibration in the process of use. Under long-term operation, the components will become loose or even loose, which will lead to "abnormal noise". When abnormal noise is found in the motor, the occurrence position of abnormal noise can be carefully analyzed in combination with the analysis of vibration, Find out the source of abnormal noise. When it is found that the abnormal sound originates from the shaft extension end of the motor, it is generally caused by the problem of the front bearing of the motor or the connection with the load; When it is found that the abnormal sound originates from the rear axle side, it is generally caused by the damage of the fan or the problem of the rear bearing; When abnormal noise is found inside the motor, it shall be shut down immediately to check whether there is chamber sweeping or loose eccentric block inside the motor. 2.2.3.3 traditional motor noise limit noise has great difficulties in real-time monitoring and early warning due to many interference factors. Generally, the noise of motor under no-load condition is tested to analyze the possible problems of motor. This paper combs the no-load noise of traditional motor, as shown in Table 3 and table 4. Table 3 noise limits for conventional motors
Table 4 noise limits of high voltage motor
2.3 abnormal electrical parameters 2.3.1 overview as an electrical equipment, electrical parameters are the most basic performance parameters. From the power consumption of the motor, it can reflect not only the running state of the motor itself, but also the working state of the load end. Moreover, compared with vibration and noise, the electrical parameters are not easy to be disturbed by the outside world, but compared with the temperature index, Electrical parameters have the advantage of rapid response; Therefore, electrical parameters are the most simple and feasible method for motor operation monitoring and abnormal warning. Commonly used electric parameter monitoring generally adopts current monitoring and voltage monitoring. 2.3.2 excessive voltage deviation endangers the motor. As an electrical equipment, the guarantee of power supply is a main index to ensure its normal operation. Excessive undervoltage will cause motor stall and excessive current. Long-term undervoltage will cause the motor and transmission line to work under overload for a long time, resulting in damage to the motor and transmission line; Overvoltage will damage the insulation of motor and transmission line, which may
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