# Power selection of asynchronous three-phase motor

Update:09 Oct 2021
Summary:The power of the asynchronous three-phase motor should be selected according to the power required by the production mac...
The power of the asynchronous three-phase motor should be selected according to the power required by the production machinery, and try to make the asynchronous three-phase motor run under the rated load. When selecting the size of the motor power, it should be based on the principle of appropriateness. It neither wastes electrical energy nor causes the motor to run overloaded for a long time. If the selected motor power is too small. There will be a "small hand-drawn cart" phenomenon, leading to long-term overload of the motor. Make its insulation layer damaged by heat. Even the motor burns out; if the selected motor power is too large. There will be a "horse cart" phenomenon. Its output mechanical power is not
Can be fully utilized, the power factor and power are not high, it will also cause electrical energy waste
Method 1: Use the formula to calculate the required power of the asynchronous three-phase motor:
(1) For the continuous operation method of constant load, if the power of the load (that is, the power on the shaft of the production machine) is known, it is Pl (kw). The required motor power P (kw) can be calculated as follows: P = P1 / n1n2, where n1 is the power of the production machinery; n2 is the power of the motor. That is the transmit power.
The power calculated according to the above formula, because the power does not have to be very accurate, the loss of mechanical energy has certain variables. The rated power of the selected asynchronous three-phase motor should be equal to or slightly greater than the calculated power. Example: The power of the machine produced is 3.95kw. Mechanical power is 70%
If you choose a motor with a power of 0.8, how much kw should the motor's power be? Solution: P = P1 / n1n2 = 3.95 / 0.7 * 0.8 = 7.1kw Since there is no 7.1kw specification, please choose 7. 5kw three-phase asynchronous motor.
(2) Asynchronous three-phase motor running for a short time. Compared with continuously running motors with the same rated power. The weight is small, the maximum torque is large, and the price is low. Therefore, when conditions permit, a three-phase asynchronous motor with a short-time work quota of S2 should be used as much as possible. The power size can also refer to the above
State the formula, which is approximately or equal to the calculation result.
(3) For asynchronous three-phase motors with intermittent operation quota S3 operating system, the power should be selected according to the size of the load duration, and the operation method should be selected for the asynchronous three-phase motors with S3 operating system specially used for intermittent operation.