电机,在设备领域是无处不在
Motors are ubiquitous in the field of equipment
这是一个不孤单的设备
It’s a device that doesn’t stand alone
靠谱的泵需要靠谱的电机
A reliable pump needs a reliable motor
电机的好坏直接影响着设备能否正常运行
The quality of the motor directly affects the normal operation of the equipment
电机类型、软启动方式,选型步骤,损坏原因方式处理方法,优劣电机区别…..这一个个问题都是电机幸福指数的重要反映。
Motor type, soft start mode, selection steps, damage cause method, treatment method, difference between good and bad motors….. These problems are an important reflection of the motor happiness index.
下面就让我们一同看看
Let’s take a look
电机基础知识01
Motor Basics 01
各类电机的区别
The difference between various types of motors
1、直流、交流电机区别
The difference between DC and AC motors
Schematic diagram of DC motor structure
![电机基础知识图文介绍 | 同步电机、异步电机、普通电机、变频电机、交流电机、直流电机](https://www.ippdd.com/wp-content/uploads/2024/02/347031.png)
Schematic diagram of AC motor structure
![电机基础知识图文介绍 | 同步电机、异步电机、普通电机、变频电机、交流电机、直流电机](https://www.ippdd.com/wp-content/uploads/2024/02/347032.png)
Name implies
DC motors use direct current as a power source.
AC motors, on the other hand, use alternating current as a power source.
Structurally speaking, the principle of DC motor is relatively simple, but the structure is complex and not easy to maintain.
The principle of AC motor is complex but the structure is relatively simple, and it is easier to maintain than DC motor.
In terms of price, DC motors with the same power are higher than AC motors.
Including the speed control device, the price of DC is higher than that of AC, of course, the structure and maintenance are also very different.
In terms of performance, due to the stable speed and accurate speed control of the DC motor, which cannot be achieved by the AC motor, the DC motor has to be used instead of the AC motor under the strict requirements of the speed.
AC motors are relatively complex to regulate speed, but they are widely used due to the use of AC power in chemical plants.
2同步、异步两类电机区别
There is a difference between synchronous and asynchronous motors
![电机基础知识图文介绍 | 同步电机、异步电机、普通电机、变频电机、交流电机、直流电机](https://www.ippdd.com/wp-content/uploads/2024/02/347033.png)
The rotor rotates at the same speed as the stator, so it is called a synchronous motor.
If it is inconsistent, it is called an asynchronous motor.
3普通、变频两类电机区别
The difference between ordinary and inverter motors
First of all, it is clear that ordinary motors cannot be used as inverter motors.
The ordinary motor is designed according to the constant frequency and constant voltage, and it is impossible to fully adapt to the requirements of the frequency converter speed regulation, so it cannot be used as a frequency conversion motor.
The influence of the inverter on the motor
Mainly in the efficiency of the motor and the temperature rise
The inverter can produce different degrees of harmonic voltage and current during operation, so that the motor runs under non-sinusoidal voltage and current, and the higher harmonics in it will cause the increase of stator copper consumption, rotor copper consumption, iron consumption and additional loss of the motor.
Among them, the most significant is the copper loss of the rotor, which will cause the motor to generate additional heat, reduce efficiency, reduce the output power, and increase the temperature rise of ordinary motors by 10%-20%.
![电机基础知识图文介绍 | 同步电机、异步电机、普通电机、变频电机、交流电机、直流电机](https://www.ippdd.com/wp-content/uploads/2024/02/347034.png)
The carrier frequency of the inverter ranges from a few thousand hertz to more than ten thousand hertz, which makes the stator winding of the motor bear a high voltage rise rate, which is equivalent to applying a steep impulse voltage to the motor, so that the inter-turn insulation of the motor can withstand a more serious test.
When ordinary motors are powered by inverters, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors will become more complicated.
The harmonics contained in the variable frequency power supply interfere with the inherent space harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces, thereby increasing the noise.
Due to the wide working frequency range of the motor and the wide range of speed changes, it is difficult for the frequencies of various electromagnetic force waves to avoid the natural vibration frequencies of each structural part of the motor.
When the frequency of the power supply is low, the loss caused by the higher harmonics in the power supply is larger; Secondly, when the speed of the switch-through motor is reduced, the cooling air volume decreases proportionally to the cubic of the speed, resulting in the heat of the motor not being dissipated, the temperature rise increases sharply, and it is difficult to achieve constant torque output. (We recommend that you pay attention to the “Mechanical Engineer” public account to grasp the knowledge of dry goods and industry information at the first time)
How to distinguish between ordinary motors and inverter motors?
The difference between the structure of ordinary motor and inverter motor
01. Higher requirements for insulation grade
Generally, the insulation grade of the inverter motor is F or higher, and the insulation strength of the ground insulation and line turns should be strengthened, especially the ability of the insulation to withstand the impulse voltage.
02. The vibration and noise requirements of the inverter motor are higher
The inverter motor should fully consider the rigidity of the motor mechanism and the whole, and try to increase its natural frequency to avoid resonance with each force wave.
03. The cooling method of the inverter motor is different
Inverter motors generally use forced ventilation cooling, that is, the main motor cooling fan is driven by an independent motor.
04. Different requirements for protective measures
Bearing insulation measures should be used for variable frequency motors with a capacity of more than 160KW. When the current generated by other high-frequency components is combined, the shaft current will increase greatly, resulting in bearing damage, so insulation measures should generally be taken. For constant power variable frequency motors, when the speed exceeds 3000/min, special grease with high temperature resistance should be used to compensate for the temperature increase of the bearing.
05. The heat dissipation system is different
The inverter motor cooling fan is powered by an independent power supply to ensure continuous heat dissipation capacity.
电机基础知识02
Motor Basics 02
电机的选型
Selection of motors
The basic contents required for motor selection are:
The type of load driven, the rated power, the rated voltage, the rated speed, and other conditions.
The type of load
DC motors
Asynchronous motor
Synchronous motors
For production machinery with stable load and no special requirements for lifting and braking, it is advisable to give preference to ordinary squirrel cage asynchronous motors, which are widely used in machinery, water pumps, fans, etc.
![电机基础知识图文介绍 | 同步电机、异步电机、普通电机、变频电机、交流电机、直流电机](https://www.ippdd.com/wp-content/uploads/2024/02/347035.png)
Winding asynchronous motors should be used for production machinery that starts and brakes more frequently and requires larger starting and braking torques, such as overhead cranes, mine hoists, air compressors, irreversible rolling mills, etc.
There is no requirement for speed regulation, and the speed needs to be constant or the power factor needs to be improved, synchronous motors should be used, such as medium and large capacity water pumps, air compressors, hoists, mills, etc.
调速范围要求在1∶3以上,且需连续稳定平滑调速的生产机械,宜采用他励直流电动机或用变频调速的鼠笼式异步电动机或同步电机,例如大型精密机床、龙门刨床、轧钢机、提升机等。
For production machinery that requires a speed regulation range of more than 1:3 and requires continuous, stable and smooth speed regulation, it is advisable to use separately excited DC motors or squirrel cage asynchronous motors or synchronous motors with frequency conversion speed regulation, such as large-scale precision machine tools, gantry planers, rolling mills, hoists, etc.
要求起动转距大,机械特性软的生产机械,使用串励或复励直流电动机,例如电车、电机车、重型起重机等。
Production machinery that requires a large starting distance and soft mechanical characteristics use series or compound excitation DC motors, such as trams, electric locomotives, heavy cranes, etc.
Generally speaking, the type of load driven, the rated power, the rated voltage, and the rated speed of the motor can be roughly determined.
However, if the load requirements are to be optimally met, these basic parameters are not sufficient.
Parameters that also need to be provided include:
Frequency, working system, overload requirements, insulation level, protection level, moment of inertia, load resistance torque curve, installation method, ambient temperature, altitude, outdoor requirements, etc. (provided according to the specific situation)
电机基础知识03
Motor Basics 03
电机故障排查步骤
Steps for motor selection
When the motor is running or malfunctioning,
Faults can be prevented and eliminated in time by seeing, hearing, smelling, and touching.
In order to ensure the safe operation of the motor.
1. Look
Observe whether there is any abnormality in the operation of the motor, which is mainly manifested in the following situations.
1. When the stator winding is short-circuited, you may see smoke coming from the motor.
2. When the motor is seriously overloaded or out of phase, the speed will slow down and there will be a heavy “hum” sound.
3. The motor maintenance network is operating normally, but when it stops suddenly, you will see sparks coming from the loose wiring; Phenomena such as a blown fuse or a stuck component.
4. If the motor vibrates violently, it may be that the transmission device is stuck or the motor is poorly fixed, the foot bolts are loose, etc.
5. If there are discoloration, burn marks and smoke marks at the contact points and connections in the motor, it means that there may be local overheating, poor contact at the conductor connection or burning of the winding.
2. Listen
When the motor is operating normally, it should emit a uniform and light “hum” sound, without noise and special sounds.
If the noise is too large, including electromagnetic noise, bearing noise, ventilation noise, mechanical friction sound, etc., it may be a precursor or fault phenomenon.
1. For electromagnetic noise, if the motor emits a high and low and heavy sound, the causes may be as follows:
(1) The air gap between the stator and the rotor is uneven, and the sound is high and low and the interval between high and low bass is unchanged, which is caused by the wear of the bearing so that the stator and the rotor are not concentrified. (We recommend that you pay attention to the “Mechanical Engineer” public account to grasp the knowledge of dry goods and industry information at the first time)
(2) Three-phase current unbalance. This is the reason that the three-phase winding has misgrounding, short circuit or poor contact, etc., if the sound is very dull, it means that the motor is seriously overloaded or out of phase operation.
(3) The iron core is loose. During the operation of the motor, the core fixing bolt is loosened due to vibration, resulting in the loosening of the core silicon steel sheet and the noise.
2. For bearing noise, it should be monitored frequently during the operation of the motor.
The monitoring method is to hold one end of the screwdriver against the bearing mounting part and the other end close to the ear, and the bearing operation sound can be heard. If the bearing is running normally, the sound is a continuous and small “rustling” sound, and there will be no high and low changes and metal friction sounds.
If the following sounds are present, it is abnormal:
(1) There is a “squeak” sound when the bearing is running, which is the sound of metal friction, which is generally caused by the lack of oil in the bearing, and the bearing should be disassembled and filled with an appropriate amount of grease.
(2) If there is a “chirping” sound, which is the sound made when the ball rotates, it is generally caused by the drying up of grease or lack of oil, and an appropriate amount of grease can be added.
(3) If there is a “click” sound or “crunch” sound, it is the sound produced by the irregular movement of the balls in the bearing, which is caused by the damage of the balls in the bearing or the long-term use of the motor and the drying up of the grease.
3. If the transmission mechanism and the driven mechanism emit continuous sound instead of high and low, it can be divided into the following situations.
(1) Periodic “popping” sound is caused by the unevenness of the belt joint.
(2) Periodic “knock” sound, caused by the loosening between the coupling or pulley and the shaft, as well as the wear of the key or keyway.
(3) The uneven collision sound is caused by the fan blade colliding with the fan cover.
3. Smell
By smelling the smell of the motor, it is also possible to detect and prevent malfunctions.
Open the junction box and sniff with your nose
If there is a special smell of paint, it means that the internal temperature of the motor is too high; If a strong mushy or burnt smell is found, it may be that the insulation repair net has been broken down or the windings have been burned.
If there is no smell, it is also necessary to use a megohmmeter to measure the insulation resistance between the winding and the shell to be less than 0.5 trillion, and it must be dried. If the resistance value is zero, it means that it has been damaged.
Fourth, touch
The cause of the fault can also be judged by touching the temperature of some parts of the motor.
In order to ensure safety, the back of the hand should be used to touch the motor housing and the surrounding parts of the bearing.
If an abnormal temperature is found, it may be due to the following reasons:
1. Poor ventilation. Such as fan falling off, ventilation duct blockage, etc.
2. Overload. As a result, the current is too large and the stator winding is overheated.
3. Stator winding inter-turn short circuit or three-phase current unbalance.
4. Frequent starting or braking.
5. If the temperature around the bearing is too high, it may be caused by bearing damage or lack of oil.
Motor bearing temperature regulations, abnormal causes and treatment
The regulations stipulate that the maximum temperature of rolling bearings should not exceed 95 °C, and the maximum temperature of plain bearings should not exceed 80 °C. And the temperature rise does not exceed 55°C (the temperature rise is the bearing temperature minus the ambient temperature at the time of the test).
Causes and treatment of high bearing temperature rise:
(1) Reason: the shaft is bent and the center line is not accurate.
Processing: Re-centering.
(2) Reason: Loose foundation screws.
Treatment: Tighten the foundation screws.
(3) Reason: The lubricating oil is not clean.
Treatment: Replace the lubricating oil.
(4) Reason: The lubricating oil has been used for too long and has not been replaced.
Treatment: Wash the bearings and replace the lubricating oil.
(5) Reason: Damage to the ball or roller in the bearing.
Treatment: Replace the bearing with a new one.
Solution(s):
1. Open the cover plate of the module and replace the damaged components such as the fuse and charging resistor in the module.
2. Replace the damaged optical flux daughter board or protection diode.
3. The optical fiber is connected normally according to the label, and the optical fiber will be replaced if it is damaged.
4. Replace the module power strip.