The basic content needed to select the correct motor model are: the type of load being driven, the rated power, the rated voltage, and the rated speed.

　　1. Rated power

　　The rated power of the motor refers to the output power, that is, the shaft power, also called the capacity. It is the most important index to quantify the motor's drag load capacity, and it is also the parameter requirement that must be considered when the motor is selected.

　　The power of the motor should be determined in the most economical and reasonable manner on the premise that the motor can meet the requirements of the production mechanical load. If the power is selected too large, the equipment investment will increase, resulting in 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 selected too small, the motor will run with overload, causing the motor to run prematurely damage.

　　2. The type of load driven

　　Motors can be simply divided into DC motors and AC motors, and AC is further divided into synchronous motors and asynchronous motors.

　　The principle of selecting a motor is that on the premise that the performance of the motor meets the requirements of the production machinery, the motor with simple structure, low price, reliable work and convenient maintenance is preferred. In this respect, AC motors are superior to DC motors, AC asynchronous motors are superior to AC synchronous motors, and squirrel cage asynchronous motors are superior to winding asynchronous motors.

　　For production machinery with stable load and no special requirements for starting and braking, ordinary squirrel-cage asynchronous motors should be preferred, which are widely used in machinery, water pumps, fans, etc.

　　Starting and braking are more frequent, and production machinery that requires larger starting and braking torques, such as bridge cranes, mine hoists, air compressors, and irreversible rolling mills, should use wound asynchronous motors.

　　Where there is no requirement for speed regulation, a constant speed or improvement of power factor is required, synchronous motors should be used, such as medium and large-capacity water pumps, air compressors, hoists, mills, etc.

　　The speed regulation range is required to be above 1:3, and the production machinery that needs continuous, stable and smooth speed regulation should adopt a separately excited DC motor or a squirrel cage asynchronous motor or synchronous motor with frequency conversion speed regulation, such as large precision machine tools, planers, Rolling mills, hoists, etc.

　　The production machinery that requires large starting torque and soft mechanical characteristics uses series-excited or compound-excited DC motors, such as trams, electric locomotives, and heavy-duty cranes.

　　3. Rated voltage

　　The rated voltage of the motor refers to the line voltage in the rated working mode.

　　The selection of AC motor voltage level mainly depends on the power supply voltage level of the place where it is used. Generally, the low voltage network is 380V, so the rated voltage is 380V (Y or △ connection), 220/380V (△/Y connection), 380/660V (△/Y connection).

　　The rated voltages of DC motors are generally 110V, 220V and 440V. Among them, 220V is a common voltage level, and high-power motors can be increased to 600~1000V.

　　4. Rated speed

　　The rated speed of the motor refers to the speed in the rated working mode.

　　The motor and the working machine dragged by it have their own rated speed. 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 should not be too high, because this will make the transmission mechanism too complicated and difficult to maintain.

　　The rotor of the motor will vibrate during operation, and the amplitude reaches the maximum at a certain speed, which is commonly referred to as resonance. The speed with the largest amplitude of the rotor is called the critical speed of the rotor.

　　When the rotor is running at a critical speed, severe vibration will occur, and the curvature of the shaft will increase significantly. Long-term operation will also cause severe bending and deformation of the shaft, or even breakage. This effect should be considered when determining the speed parameters to avoid long-term use of the motor in the critical speed range.

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

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