How to choose the motor protection type and its voltage and speed?

There are many types of protection for motors. In practical selection, suitable protection type motors must be selected according to different working environments. The protection type of the motor includes open type, protective type, closed type, explosion-proof type, submersible type and so on.

1. Selection of motor protection type

There are many types of protection for motors. In practical selection, suitable protection type motors must be selected according to different working environments. The protection type of the motor includes open type, protective type, closed type, explosion-proof type, submersible type and so on. Usually, the open type is selected 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 harmless and easy to be blown out by compressed air, the protective type can be selected. As for the motor for submersible pumps, it should be completely sealed to ensure that moisture is not intruded when working in water.

How to choose the motor protection type and its voltage and speed?

2. Selection of motor voltage and speed

(1) When selecting motors for the production machinery of existing factories and enterprises, the rated voltage of the motor should be consistent with the distribution voltage of the factory. For motors in new factories, the voltage selection should be considered together with the selection of the power supply and distribution voltage of the factory. According to different voltages The grades are selected based on technical and economic comparisons. The low voltage standard stipulated in my country is 220/380V, and most of the high voltage distribution voltage is 10KV. Generally, motors with small and medium capacity are mostly low-voltage, and their rated 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 editor tells you that the selection of the (rated) speed of the motor should be considered according to the requirements of the driving production machinery and the ratio of the transmission device. The number of revolutions per minute of the motor is usually 3000, 1500, 1000, 750 and 600. The rated speed of the asynchronous motor is generally 2% to 5% lower than the above speed due to the existence of slip. From the perspective of motor manufacturing, if the rated speed of the motor with the same power is higher, the 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 driven machine is too large, the number of transmission stages that need to be installed will be more. It will increase the equipment cost and the energy loss of the transmission. Therefore, it is necessary to analyze and compare the best choice. Most of the motors we usually use are 4-pole 1500r/min motors, because this rated speed motor has a wide range of applications, and its power factor and work efficiency are also high.

Author: Yoyokuo