Electric motors are firmly entrenched as the most important components of most devices used by humans every day. One of the types of electric machines for rotating the working body is a synchronous electric motor. We will consider the features of the device and the principle of operation of a synchronous motor further.
Device
Structurally, any synchronous unit is a stator and a rotor combined in one housing. The stator winding is wound into the slots of a stationary magnetic circuit, assembled from a ferromagnetic material. The rotor structure can include a winding mounted on a steel frame or a permanent magnet mounted on a shaft. The task of both one and the second is to create a magnetic flux interacting with the stator electromagnetic field.
Principle of operation
On the basis of clause 53 of GOST 27471-87, the concept of a synchronous motor implies a contactless machine operating on alternating current. In which, in the steady state, the ratio of the rotor speed to the current frequency in the armature windings does not depend on the magnitude of the load at rated operation.
From a practical point of view, it looks like this:
- a three-phase voltage is applied to the stator windings, also called an armature;
- as the amplitude of the sinusoid in one phase increases, the current and the electromagnetic field created around the winding will proportionally increase;
- in view of the fact that the sinusoid increases in all three phases of the motor alternately, the peak of the maximum electromagnetic field will shift from one winding to another clockwise;
- the magnetic field of the rotor (inductor) is alternately attracted by its own poles to the opposite sign of the stator field vector.
As a result of this interaction, translational rotation of the synchronous motor shaft around its axis occurs. Since power lines formed by an independent source are constantly present in the inductor, the frequency of its rotation fully corresponds to the frequency of the voltage supplied to the armature windings. Synchronism occurs in the motor.
Types of synchronous motors
In general, synchronous motors are divided into several categories, depending on their design features.
So, to obtain a flux of excitation use:
- rotor winding - to ensure electromagnetic interaction, power is supplied to the winding from a third-party source;
- magnetic rotor - the auxiliary magnetic field of the rotor is created by permanent magnets installed on it;
- jet rotor - the shape of the magnetic circuit of the inductor is made in such a way that the lines of force of the armature are refracted to obtain synchronous rotation.
Depending on the design of the rotor, a salient pole and an implicit pole synchronous motor are distinguished.
According to the operating mode, they can be used as an electric motor, generator or synchronous compensator.
Operating modes
In practice, each electric machine can be used in different operating modes:
- Engine mode - the unit operates on the principle of converting electrical energy into mechanical energy. Voltage is applied to the armature leads and converted into rotational force on the rotor.
- Generator mode - in this case, the motor shaft rotates due to the turbine or other object, and the generated voltage is removed from the armature leads.
- Synchronous compensator - the electric motor is connected to the distribution network at idle speed. This increases the power factor of the system due to the consumption of reactive power.
P.S. More other details about synchronous motor, and also about how it differs from an induction motor, see the video: