The reference standards for motor selection mainly include: motor type, voltage and speed; motor type and type; motor protection type selection; motor voltage and speed.
Motor selection should refer to the following conditions:
1. The type of power supply for the motor, such as single-phase, three-phase, DC, etc.
2. The operating environment of the motor, whether the motor operating occasion has special characteristics, such as humidity, low temperature, chemical corrosion, dust, etc.
3. The operation method of the motor is continuous operation, short-term operation or other operation methods .
4. The assembly method of the motor, such as vertical assembly, horizontal assembly, etc.
5. The power and speed of the motor, etc., the power and speed should meet the requirements of the load .
6. Other factors, such as whether it is necessary to change speed, whether there is a special control request, the type of load, etc.
1. Selection of motor type, voltage and speed
When choosing the type of motor, the details of voltage and speed, and the usual steps , it is mainly based on the requirements of the production machine for the electric drive, such as the frequency level of starting and braking, whether there is a speed regulation requirement, etc. to select the current type of the motor. That is to say, choose an alternating current motor or a DC motor; secondly, the size of the motor’s extra voltage should be selected in conjunction with the power supply environment; then its extra speed should be selected from the speed required by the production machine and the requirements of the transmission equipment; and then according to the motor and production machine. The surrounding environment determines the layout type and protection type of the motor; finally, the extra power (capacity) of the motor is determined by the power size necessary for the production machine. Based on the above considerations, finally select the motor that meets the requirements in the motor product catalog. If the motor listed in the product catalog cannot meet some special requirements of the production machine, it can be individually customized to the motor manufacturer.
2. Selection of motor type and type
The selection of the motor is based on AC and DC, machine characteristics, speed regulation and starting performance, protection and price, etc., so the following criteria should be followed when selecting:
1. First, choose a three-phase squirrel-cage asynchronous motor. Because it has the advantages of simplicity, durability, reliable operation, low price and convenient maintenance, but its shortcomings are difficult speed regulation, low power factor, large starting current and small starting torque. Therefore, it is mainly suitable for ordinary production machines and drives with hard machine characteristics and no special speed regulation requirements, such as ordinary machine tools and production machines such as pumps or fans with a power less than 100KW .
2. The price of the wound motor is higher than that of the cage motor, but its mechanical characteristics can be adjusted by adding resistance to the rotor, so it can limit the starting current and increase the starting torque, so it can be used for small power supply capacity. Where the motor power is large or there is a speed regulation requirement, such as some lifting equipment, hoisting and lifting equipment, forging presses and beam movement of heavy machine tools, etc.
3. When the speed regulation scale is lower than 1:10 , and it is required to be able to adjust the speed smoothly, the slip motor can be selected first. The layout type of the motor can be divided into two types: horizontal type and vertical type according to the difference of its assembly position. The shaft of the horizontal motor is assembled horizontally, and the shaft of the vertical motor is assembled vertically to the height, so the two motors cannot be interchanged. Under normal circumstances, you should only choose a horizontal motor. As long as it is necessary to run vertically (such as vertical deep well pumps and drilling machines, etc.), in order to simplify the transmission assembly, the vertical motor should be considered (because it is more expensive) .
3. Selection of motor protection type
There are many types of protection for the motor. When selecting the application, the appropriate protection type motor must be selected according to different operating environments. The protection type of the motor includes open type, protective type, closed type, explosion-proof type, submersible type and so on. Choose the open type in the usual environment because it is cheap, but it is only suitable for dry and clean environments. For humid, weather-resistant, dusty, flammable, and corrosive environments, the closed type should be selected. When the insulation is harmful and it is easy to be blown out by compressed air, the protective type can be selected. As for the motor for submersible pumps, a completely sealed type should be adopted to ensure that moisture is not intruded when operating in water. When the motor is in an environment with a risk of fire or explosion, it should be noted that the explosion-proof type must be selected.
Fourth, the selection of motor voltage and speed
1. When selecting a motor for the production machine of an existing factory enterprise, the additional voltage of the motor should be the same as the power distribution voltage of the factory. The voltage selection of the motor of the new factory should be considered together with the selection of the power supply and distribution voltage of the factory, according to the different voltage levels. After technical and economic comparison, the best decision will be made.
The low voltage standard stipulated in China is 220/380V , and most of the high voltage is 10KV . In general, most of the small and medium-capacity motors are high-voltage, and their additional voltages are 220/380V ( D/Y connection) and 380/660V (D/Y connection ) . When the motor capacity exceeds about 200KW , it is recommended that the user choose a high-voltage motor of 3KV , 6KV or 10KV .
2. The selection of the (extra) speed of the motor should be considered according to the requirements of the production machine and the ratio of the transmission assembly. The number of revolutions per minute of the motor is usually 3000 , 1500 , 1000 , 750 and 600. The extra speed of the asynchronous motor is usually 2 % to 5% lower than the above speed because of the slip rate . From the perspective of motor production, if the additional speed of a motor of the same power is higher, the shape and size of its electromagnetic torque will be smaller, the cost will be lower and the weight will be lighter, and the power factor and efficiency of high-speed motors are higher than those of low-speed motors. If you can choose a motor with a higher speed, the economy will be better, but if the speed difference between the motor and the machine to be driven is too large, the more transmission stages need to be installed to accelerate the device, which It will increase the equipment cost and the energy consumption of the transmission. Explain the comparison and selection. Most of the motors we usually use are 4 -pole 1500r/min motors, because this type of motor with extra speed has a wide range of applications, and its power factor and operating efficiency are also high.
Post time: Jun-11-2022