The power of the motor. It should be selected according to the power required by the production machine, and the motor should be operated under the rated load as much as possible. Pay attention to the following two points when choosing:
(1) If the motor power is too small, there will be a phenomenon of “small horse-drawn cart”, causing the motor to be overloaded for a long time. The insulation is damaged by heat. Even the motor is burnt.
(2) If the motor power is selected too large. There will be a "big horse car" phenomenon. The output mechanical power cannot be fully utilized, and the power factor and efficiency are not high (see table), which is not only bad for users and the power grid. It also causes a waste of electricity.
To properly select the power of the motor, the following calculations or comparisons must be made:
(1) For a constant load continuous operation mode, if the power of the load (ie, the power on the production machine shaft) is known (Pl(kw). The power P(kw) of the required motor can be calculated as follows: P=P1/n1n2
Where n1 is the efficiency of the production machine; n2 is the efficiency of the motor. That is, transmission efficiency.
The power obtained by the above formula is not necessarily the same as the power of the product. therefore. The rated power of the selected motor should be equal to or slightly greater than the calculated power.
Example: The power of a production machine is 3.95kw. The mechanical efficiency is 70%. If a motor with an efficiency of 0.8 is selected, how much kw should the power of the motor be?
Solution: P=P1/ n1n2=3.95/0.7*0.8=7.1kw Since there is no 7.1kw this specification. So choose 7.5kw motor.
(2) Short-time work quota motor. Compared with a motor with the same continuous working rating. The maximum torque is large, the weight is small, and the price is low. Therefore, when conditions permit, try to use a motor with a short-time working quota.
(3) For the motor with intermittent working quota, the power selection should be based on the magnitude of the load duration, and the motor specially used for the intermittent operation mode should be selected. The formula for the load continuous string Fs% is FS%=tg/(tg+to)×100%
Where tg is the working time, t. To stop the time min; tg ten to is the duty cycle time min.