Can an asynchronous motor generate electricity?
Many readers have reported that the state of power generation of asynchronous motors, if it is to be understood, it is not difficult: when the direction of the rotor current is reversed, it becomes a state of power generation. But when you think about it carefully, you always feel that it is not clear: how does the phase angle of the stator current change after the rotor current is reversed? Is there an asynchronous generator? The author experimented with a popular and in-depth explanation method and achieved good results.
A generator is a device that converts mechanical energy into electrical energy. That is to say, by rotating a rotor of a motor with a prime mover (turbine, diesel, turbine, etc.), electric energy can be generated, that is, power generation.
Any motor is reversible and can be used both as an electric motor and as a generator. Asynchronous motors are no exception, but they have their particularities.
Particularity of asynchronous generator
First look at how other generators generate electricity?
(1) DC generator
The stator of the DC generator is a magnetic pole, and the rotor is an armature winding, as shown in Figure a.
When the prime mover drives the rotor to rotate, the armature winding generates an induced electromotive force by cutting the stator magnetic field, and the DC voltage is obtained by the commutator and the brush.
(2) Synchronous generator
The stator of the synchronous generator is a three-phase winding, and the rotor is a magnetic pole, as shown in Figure b.
When the prime mover drives the rotor to rotate, the three-phase winding of the stator cuts the rotor magnetic field to generate an induced electromotive force, thereby outputting a three-phase alternating voltage.
(3) Common features of DC generators and synchronous generators
1) They all have a fixed magnetic field;
2) Under the driving of the prime mover, the windings cut the magnetic lines of force and "send" the electricity from the endless.
(4) Particularity of asynchronous generator
The stator of an asynchronous machine is a three-phase winding, and the rotor is a short-circuit winding and has no magnetic field itself. Therefore, the asynchronous motor is only powered by the prime mover. Although, in theory, the use of residual magnetism can also generate electricity, but it has no practical significance.
In order for an asynchronous motor to generate electricity, it is first necessary to establish a magnetic field. However, as is well known, an asynchronous motor generates a rotating magnetic field after a three-phase alternating current is passed through the three-phase winding of the stator. That is to say, in order to obtain a magnetic field, the asynchronous winding of the asynchronous motor must be connected to the three-phase power supply, as shown in Figure c. There is no doubt that in this case it will work as an asynchronous motor. However, if a prime mover is used to drive the rotor to exceed the synchronous speed, it becomes an asynchronous generator.
Therefore, asynchronous motors cannot generate electricity independently from scratch, which is its particularity.
