Principle of alternating current

When the coil passes through the neutral plane, the current will change direction, the coil rotates once, twice through the neutral plane, the current direction will change twice. The logarithm of the positive and negative magnetic fields in the actual motor can have 1 pair, 2 pairs, 3 pairs, and 5 pairs. Therefore, the frequency of the AC power emitted F=1/T=nP/60, where n represents the number of poles, P represents the speed of the coil, the unit is rap/min, F represents the frequency, the unit is Hz, 60 is per minute (second).

China stipulates that the standard power supply frequency is f=50 cycles/second, that is, the power frequency is 50Hz, so the speed of the rotating magnetic field is only related to the number of magnetic poles. The number of magnetic poles is large, and the rotational speed of the rotating magnetic field is low. When the pole number P=1, the rotational speed n=3000; When the number of poles P=2, the rotational speed n=1500; When the pole number P=3, the rotational speed n=1000; When the pole number P=4, the rotational speed n=750; When the pole number P=5, the rotating magnetic field speed n=600 (in fact, due to the existence of slip rate, motor. The actual speed is slightly lower than that of the rotating magnetic field)

In the frequency conversion speed regulation system (the basic principle of the engine and the motor is the same), according to the formula n=60f/p, we can see:

Change the frequency f to change the speed

Reduce the frequency ↓f, the speed becomes smaller: that is, 60 f↓ / p = n↓

Increasing the frequency ↑f increases the speed: 60 f↑ / p = n↑.

In summary, alternating current is a sine wave, and the frequency of electricity is determined by the number of poles and the speed of the generator.