The power of the motor should be selected according to the power required by the production machinery, and try to make the motor run under the rated load. When choosing, you should pay attention to the following two points:

①If the motor power is too small. There will be a phenomenon of "small horse-drawn cart", which will cause the motor to be overloaded for a long time. Its insulation is damaged due to heat. Even the motor was burned out.

②If the motor power is too large. There will be a "big horse-drawn cart" phenomenon. Its output mechanical power cannot be fully utilized, and the power factor and efficiency are not high, which is not only unfavorable to users and the power grid. And it will also cause waste of electricity.

To correctly select the power of the motor, the following calculations or comparisons must be made:

P=F*V/1000(P=calculated power KW, F=required pulling force N, working machine linear speed M/S)

For constant load continuous operation, the required motor power can be calculated as follows:

P1(kw): P=P/n1n2

In the formula, n1 is the efficiency of the production machinery; n2 is the efficiency of the motor, that is, the transmission efficiency.

The power P1 obtained by the above formula is not necessarily the same as the product power. therefore. The power rating of the selected motor should be equal to or slightly greater than the calculated power.

also. The most commonly used is the analogy method to select the power of the motor. The so-called analogy. It is compared with the power of the motors used in similar production machinery.

The specific method is: to know how much power motor is used by similar production machinery in this unit or other nearby units, and then select a motor with similar power for test run. The purpose of the test run is to verify that the selected motor matches the production machine.

The verification method is: make the motor drive the production machinery to run, measure the working current of the motor with a clamp ammeter, and compare the measured current with the rated current marked on the motor nameplate. If the actual working current of the motor is not much different from the rated current marked on the spleen. It indicates that the power of the selected motor is suitable. If the actual working current of the motor is about 70% lower than the rated current marked on the nameplate. It indicates that the power of the motor is too large, and the motor with lower power should be replaced. If the measured working current of the motor is more than 40% larger than the rated current marked on the nameplate. It indicates that the power of the motor is too small, and the motor with larger power should be replaced.

In fact, torque (torque) should be considered, and there are calculation formulas for motor power and torque.

That is T=9550P/n

where:

P—power, kW;

n—the rated speed of the motor, r/min;

T—torque, Nm.

The output torque of the motor must be greater than the torque required by the working machine, and a safety factor is generally required.