Cooling tower motor characteristics and basic knowledge（3）

Formula of motor speed and frequency

n=60f/p
n——Motor speed (rev / min);
60——Every minute (seconds)；
f——Power frequency (Hz)；
p——The number of pole pairs of the rotating magnetic field of the motor.

China stipulates that the standard power supply frequency is f=50 cycles/second, so the rotational speed of the rotating magnetic field is only related to the number of magnetic pole pairs.The number of pole pairs is large, and the rotational speed of the rotating magnetic field is lower.

When the pole pair P=1, the rotational speed of the rotating magnetic field is n=3000;

When the pole pair P=2, the rotational speed of the rotating magnetic field is n=1500;

When the pole pair P=3, the rotational speed of the rotating magnetic field is n=1000;

When the pole pair P=4, the rotational speed of the rotating magnetic field is n=750;

When the pole pair P=5, the rotational speed of the rotating magnetic field is n=600.

(In fact, due to the slip rate, the actual motor speed is slightly lower than the rotating magnetic field.)
In the variable frequency speed control system, according to the formula n=60f/p:

Change the frequency f to change the speed

Reducing the frequency ↓f, the speed becomes smaller: 60 f↓ / p = n↓;
Increase the frequency ↑f and increase the speed: 60 f↑ / p = n↑.