Take you to understand the structure and working principle of the three-phase alternator in one minute

The three-phase alternator is one of many generators. Its structure and composition determine the working principle of the current generated by the three-phase alternator, and its power and excitation mode determine that the three-phase alternator has different classifications. In this article, JUNVOCH, a generator manufacturer, will introduce you to the professional knowledge of three-phase alternators in detail.

 

The structure of the three-phase alternator

1. The three-phase alternator is composed of stator, rotor, end cover, frame, brush and bearing.​​

2. The stator consists of the frame, the stator core, the coil winding and other structural parts that fix these parts. The rotor is composed of rotor core, rotor magnetic pole, fan, slip ring and rotating shaft.

3. The three-phase alternator connects the stator and rotor of the generator through the frame, bearing and end cover, so that the rotor can rotate in the stator, and a certain excitation current is passed through the slip ring, so that the rotor becomes a rotating magnetic field. The stator coil performs the motion of cutting the magnetic field lines, thereby generating an induced potential, which is drawn out through the terminals and connected to the loop to generate a current.

 

 Three-phase alternator working principle

 The three-phase alternator uses the principle of electromagnetic induction that the wire cuts the magnetic line of force to induce the potential, and converts the mechanical energy of the prime mover into electrical energy output. A synchronous generator consists of a stator and a rotor. The stator is the armature that generates electricity, and the rotor is the magnetic pole. The stator consists of armature iron core, three-phase windings evenly distributed, frame and end cover. The rotor is usually a hidden pole type, consisting of an excitation winding, an iron core and a shaft, a guard ring, a ring, and the like.

 

The excitation winding of the rotor is fed with a DC current to generate a nearly sinusoidal distributed magnetic field (called the rotor magnetic field), and its effective excitation flux is interlinked with the stationary armature winding. When the rotor rotates, the magnetic field of the rotor rotates along with it, and the magnetic field line cuts each phase winding of the stator sequentially, and a three-phase AC potential is induced in the three-phase stator winding. When the generator runs with a symmetrical load, the three-phase armature currents combine to generate a rotating magnetic field with a synchronous speed. The interaction between the stator magnetic field and the rotor magnetic field produces braking torque. The mechanical torque input from the steam turbine overcomes the braking torque to perform work. The generator can generate active power and reactive power. Therefore, to adjust the active power, it is necessary to adjust the steam intake of the turbine. The strength of the rotor magnetic field directly affects the voltage of the stator winding, so the rotor current must be adjusted to adjust the generator terminal voltage or adjust the reactive power of the generator.

 

Classification of excitation methods of three-phase alternators

The generator excitation system refers to a system that supplies DC to the generator rotor to establish rotor excitation. It is further divided into:

1. It is an excitation system. Its excitation is generated by an alternating current generator coaxial with the generator, which is rectified into direct current to excite the rotor of the generator.

2. The self-parallel excitation magnetic system is to step down the alternating current from the generator end through the transformer, and then rectify it into direct current, which is used as the excitation of the generator rotor.