background knowledge
Induction motor is also known as "asynchronous motor", that is, the rotor is placed in a rotating magnetic field, and under the action of the rotating magnetic field, a rotational torque is obtained, so the rotor rotates.
The rotor is a rotatable conductor, usually in the shape of a squirrel cage. The stator is the non-rotating part of the motor and its main task is to generate a rotating magnetic field. The rotating magnetic field is not achieved mechanically. Instead, alternating current is passed through several pairs of electromagnets, so that the properties of the magnetic poles are cyclically changed, so it is equivalent to a rotating magnetic field.
This kind of motor does not have brushes or collector rings like DC motors. There are single-phase motors and three-phase motors according to the type of AC power used. Single-phase motors are used in washing machines, electric fans, etc.; three-phase motors are used as power for factories. equipment.
Back EMF refers to the tendency to resist current changes and generate electromotive force, which is essentially an induced electromotive force. Back EMF generally appears in electromagnetic coils, such as relay coils, solenoid valves, contactor coils, motors, inductors, etc.
When the DC motor is initially started, the excitation winding establishes a magnetic field, the armature current generates another magnetic field, and the two magnetic fields interact to start the motor. The armature windings rotate in a magnetic field, thus creating a generator effect. In fact, the rotating armature generates an induced electromotive force, which is opposite to the polarity of the armature voltage. This self-induced electromotive force is called back electromotive force.
emf usually means electromotive force, but since it's not a "force" in the physical sense, it doesn't help, but back emf is still used in motors as self-induced electromotive force. Back EMF, also known as back EMF, can significantly reduce the armature current when the motor is running at a constant speed.
question of the day
Here is the approximate equivalent circuit I found for the rotor inside an induction motor, which seems to introduce a variable resistance. Is this R2(1-s/s) formed because of the back EMF? Is this a "sensing resistance value" or a voltage drop due to slip?