Motor speed issue

“The idea that “the greater the power, the faster the speed” is wrong!

The speed of the motor is determined by the power supply frequency and the number of pole pairs it has, and it has no direct relation to power.

This post was last edited by zyz8438 on 2010-11-14 21:24: r=60f/n, where f is the frequency and n is the number of pole pairs

Reply 1# wanyuanchen: The power of a motor refers to its ability to output mechanical energy, thereby enabling it to drive mechanical loads. The speed of an AC motor is determined by the frequency of the power supply and the number of pole pairs in the motor. Under the condition of a grid frequency of 50 Hz in our country, the more pole pairs a motor has, the slower its speed. For example: when the frequency f = 50 Hz and the number of pole pairs r = 2 (with a total of 4 poles). Rotational speed n = 60f/r = 60*50/2 = 1500 rpm ； When the pole count r = 4 (with a total of 8 poles). Rotational speed n = 750 rpm 　　

Reply to 1# wanyuanchen: For the speed of a DC motor, below the base speed (the rated speed) at the rated excitation current, the speed increases as the armature voltage rises until it reaches the rated speed. Above the base speed (rated armature voltage), the speed increases as the excitation current decreases until it reaches the maximum speed.

There is a certain relationship between the speed of the rotating magnetic field, the number of pole pairs, and the frequency of the stator current. In a rotating magnetic field with two poles, as the current completes one cycle, the magnetic field rotates 360° (one full turn) in space ； In a rotating magnetic field with two poles, as the current completes one cycle, the magnetic field rotates 180° (1/2 turn) in space ； By analogy, when the rotating magnetic field has p pairs of poles, as the current completes one cycle, its rotating magnetic field rotates 1/p turns in space. ? The normal rotation speed is expressed in revolutions per minute; therefore, the formula for calculating the rotation speed of a rotating magnetic field is n1 = 60f1/p. Thus, the rotation speed n1 depends on the power supply frequency f and the number of pole pairs p

Under variable-frequency conditions, it is consistent with your understanding. Is it energy-efficient?

There is no direct relationship between motor power and speed; for example, household hair dryers have a speed of over 10,000 revolutions per minute, haha

We are currently using 380V motors, with frequency converters used to adjust their speed. While adjusting the speed, the frequency converters also modify the voltage, thereby changing the power

The formula for the speed of an asynchronous motor is: n=60f(1-s)/p, where n is the speed, f is the frequency, s is the slip rate, and p is the number of pole pairs. It can be seen that there are several main factors that affect the speed of an asynchronous motor: frequency (which is why frequency converters are used), the number of pole pairs (determined at the time of manufacturing by the manufacturer), and the slip rate (related to the operating condition of the motor). Actually, for asynchronous motors, their output power does have some influence on their speed. Why is that? Due to the change in the motor’s output power, the operating conditions of the motor change, and as a result, the motor’s slip rate s experiences slight variations. Generally speaking, the heavier the load, the greater the slip rate s, and the motor speed decreases accordingly. It’s just that this change is very subtle and hard to detect. But we can make an extreme assumption: assume that the load is infinite, and the motor’s output power has reached its limit; in this case, the motor will stall, that is, it will get stuck, and its speed will drop to 0. (Without considering the operation of current rise protection)