AC motor stator winding does not turn, why the back EMF?
When the current is energized, the coil almost does not move and the current is the maximum. The torque generated by the ampere force is much greater than the resistance torque, and the coil begins to rotate. When it starts to turn coil cutting magnetic line, resulting in a "reverse EMF E" in the coil, and the coil loading external potential U (external power supply) play a role in contrast, reducing the current. At the beginning, the reverse electromotive force is very small, the current is very large, the torque of the ampere force is larger, and the speed is increasing gradually. As the speed increases, the reverse electromotive force increases, and the current in the coil decreases. The torque of the ampere force decreases to the maximum speed of the motor when it is against the resistance torque.
The principle of an electric motor can be understood in junior high school. It is a device that transforms electrical energy into mechanical energy. The energized coil is subjected to a magnetic field to its ampere force in the magnetic field, causing the coil to rotate around the shaft. Ampere force is the power source of coil rotation. If we see only the power of the ampere force, the coil of the motor will continue to accelerate, which is obviously impossible because each motor has a maximum speed.
Back EMF is the electromotive force in the opposite direction of the electromotive force of the power supply. EMF may occur when there are multiple power supplies in the circuit. For example, the two metal bars on the same rail circuit cut the magnetic field at different speeds, and there may be a counter electromotive force; the electromotive force and the induced electromotive force exist simultaneously, and the back EMF may occur. For the coil, when the current of the winding changes, both ends of the coil will generate back electromotive force. For example, in the LC oscillating circuit, the change of the voltage at the two ends of the inductance coil is closely related to the counter electromotive force. When the motor coil turns, the back EMF is also generated.
According to the electromagnetic law, when the magnetic field changes, the nearby conductor will produce an induced electromotive force, which is in accordance with Faraday's law and Lenz's law, and the original voltage at the opposite end of the coil is reversed. This voltage is the back electromotive force.
