Relation between motor power and speed Motor power: P=1.732×U×I×cosφ Motor torque: T=9549×P\/n; Motor speed: n=60f\/p, p is the motor pole number, such as p=2 of the four-stage motor; Note: When the frequency reaches 50Hz, the motor reaches the rated power, and then increase the frequency, the power will not increase again, and the rated power will be maintained.
When the motor torque is below 50Hz, it is proportional to the frequency. When the frequency f reaches 50Hz, the motor reaches the maximum output power, that is, the rated power; If the frequency f continues to increase after 50Hz, the output torque changes inversely with the frequency, because its output power is so large, you have to continue to increase the frequency f, then the torque will be significantly reduced by the above calculation analysis.
The situation of speed and frequency is the same, because the power supply voltage is unchanged, the change in frequency is the result of the direct reaction of the change in speed, the frequency increases, the speed increases, it decreases the other one also decreases. The voltage analysis is a little tricky, you look at these formulas first.
The stator voltage of the motor: U = E I×R (I is the current, R is the electronic resistance, E is the induction potential); And: E = k×f×X (k: constant, f: frequency, X: flux); For asynchronous motors: T=K×I×X (K: constant, I: current, X: magnetic flux); It is easy to see the change of frequency f, also accompanied by the change of E, the stator voltage should also be changed, in fact, the commonly used frequency converter speed regulation method is like this, when the frequency changes, the output voltage of the frequency converter, that is, the voltage added to both ends of the stator is also changed, is proportional to the constant V\/f ratio frequency conversion method. These three equations can also be used in the previous analysis to get the same result.