The basic contents required for motor selection are: driven load type, rated power, rated voltage, rated speed, and other conditions.

1. The type of load to be driven is inversely said from the characteristics of the motor. Motors can be simply divided into DC motors and AC motors, and AC is further divided into synchronous motors and asynchronous motors.

The advantages of the DC motor can easily adjust the speed by changing the voltage, and can provide a large torque. It is suitable for loads that need to adjust the speed frequently, such as rolling mills in steel mills, hoists in mines, etc. But now with the development of frequency conversion technology, the AC motor can also adjust the speed by changing the frequency. However, although the price of variable frequency motors is not much more expensive than ordinary motors, the price of frequency converters occupies a major part of the whole set of equipment, so another advantage of DC motors is that they are cheap. The disadvantage of DC motors is that the structure is complex. As long as any equipment has a complex structure, it will inevitably lead to an increase in the failure rate. Compared with AC motors, DC motors are not only complicated in windings (excitation windings, commutation pole windings, compensation windings, armature windings), but also add slip rings, brushes and commutators. Not only the process requirements of the manufacturer are high, but the maintenance cost in the later period is also relatively high. Therefore, DC motors in industrial applications are in an embarrassing situation where they are gradually declining but still have a place in the transitional stage. If the user has sufficient funds, it is recommended to choose the scheme of AC motor with frequency converter.

2. Asynchronous motor

The advantages of asynchronous motors are simple structure, stable performance, convenient maintenance and low price. And the manufacturing process is also the simplest. I have heard from an old technician in the workshop that it takes two synchronous motors or four asynchronous motors of similar power to assemble a DC motor. This is evident. Therefore, asynchronous motors are the most widely used in industry.

2. Rated power

The rated power of the motor refers to the output power, that is, the shaft power, also known as the capacity, which is the iconic parameter of the motor. People often ask how big the motor is. Generally, it does not refer to the size of the motor, but to the rated power. It is the most important indicator to quantify the motor’s drag load capacity, and it is also the parameter requirements that must be provided when the motor is selected.

The principle of correctly selecting the motor capacity should be the most economical and most reasonable decision on the power of the motor under the premise that the motor can meet the requirements of the production mechanical load. If the power is too large, the equipment investment will increase, causing waste, and the motor often runs under load, and the efficiency and power factor of the AC motor are low; on the contrary, if the power is too small, the motor will be overloaded, causing the motor to run prematurely. damage. There are three factors that determine the main power of the motor: 1) the heating and temperature rise of the motor, which are the most important factors in determining the power of the motor; 2) the short-term overload capacity is allowed; 3) the starting capacity should also be considered for the asynchronous squirrel cage motor.

3. Rated voltage

The rated voltage of the motor refers to the line voltage in the rated working mode. The choice of the rated voltage of the motor depends on the power supply voltage of the power system to the enterprise and the size of the motor capacity.

The motor and the working machinery driven by it have their own rated speed. When choosing the speed of the motor, it should be noted that the speed should not be too low, because the lower the rated speed of the motor, the more the number of stages, the larger the volume and the higher the price; at the same time, the speed of the motor should not be too selected. high, as this would make the transmission too complex and difficult to maintain. In addition, when the power is constant, the motor torque is inversely proportional to the speed.

Generally speaking, the motor can be roughly determined by providing the type of load driven, the rated power, rated voltage, and rated speed of the motor. However, these basic parameters are far from sufficient if the load requirements are to be optimally met. Parameters that also need to be provided include: frequency, working system, overload requirements, insulation class, protection class, moment of inertia, load resistance torque curve, installation method, ambient temperature, altitude, outdoor requirements, etc., which are provided according to specific conditions.