How to choose the right motor
The power of the motor should be selected according to the power required by the production machinery, and the motor should run under the rated load as far as possible. The following points should be paid attention to when choosing:
(1) If the motor power is too small. There will be "small horse big car" phenomenon, resulting in long-term overload of the motor. The insulation is damaged by heat. Even the motor gets burned.
(2) If the motor power is too large. There will be a "big horse small car" phenomenon. Its output mechanical power can not be fully utilized, power factor and efficiency are not high, not only to the user and the power grid. It also wastes electricity.
To correctly select the motor power, the following calculations or comparisons must be made:
P=F*V/1000(P= calculated power KW, F= required tension N, working machine linear speed M/S)
For constant load continuous working mode, the required motor power can be calculated according to the following formula:
P1 (kw) : P = P/n1n2
Where n1 is the efficiency of production machinery; N2 is the efficiency of the motor, namely the transmission efficiency.
According to the above formula, the power P1 may not be the same as the product power. Therefore, the rated power of the selected motor should be equal to or slightly greater than the calculated power.
In addition, the most commonly used method is to choose the power of the motor by analogy. This is called analogy. It is compared to the power of a motor used in a similar production machine.
The specific approach is to understand the use of similar production machinery of the unit or other nearby units of high power motor, and then choose similar power motor for test run. The purpose of the test run is to verify whether the selected motor matches the production machine.
The method of verification is: the motor drives the production machinery to run, and the working current of the motor is measured with a clamp ammeter, and the measured current is compared with the rated current marked on the nameplate of the motor. If the actual working current of the motor is not much different from the rated current marked on the spleen. It shows that the power of the selected motor is appropriate. If the actual operating current of the motor is about 70% lower than the rated current marked on the nameplate. It shows that the power of the motor is too large, should be replaced with a smaller power motor. If the measured motor operating current is more than 40% greater than the rated current marked on the nameplate. It shows that the power of the motor is too small, should replace the larger power of the motor.
In fact, it should be considered torque (torque), motor power and torque are calculated by formula.
T = 9550 p/n
P -- power, kW;
N -- Rated speed of the motor, r/min;
T minus torque, Nm.
The output torque of the motor must be greater than the torque required by the working machinery, which generally requires a safety factor.