Basic structure and working principle of three-harmonic excitation three-phase alternator

Basic structure

The third harmonic excitation three-phase alternator is based on the brushed three-phase synchronous generator structure shown in Figure 3-4 . In addition to the main winding embedded in the stator core slot, a third harmonic secondary winding and base are embedded. Wave secondary winding. The expansion diagram of the stator winding is shown in Figure 3-86 and Figure 3-87.

(1) Third harmonic secondary winding. The third harmonic secondary winding is a winding with a winding pitch of 1/3 of the stator slot pitch. It can also be said that the total number of poles of the third harmonic secondary winding per phase is three times that of the generator. Taking a generator with 4 poles and a total number of slots of 36 slots as an example, the stator slot pitch = 36 ÷ 4 = 9 slots, then the winding pitch of the third harmonic secondary winding = 1/3 × 9 = 3 slots The groove pitch of the welt is 1-4. The total number of poles of the second harmonic secondary winding of this generator = 9 × 4 = 12 poles. The third harmonic secondary winding has a single phase and three phases. The third-harmonic secondary winding of a typical low-power generator uses a single phase, and its structure is the simplest. Large power secondary winding of the third harmonic generator using the multi-phase, which is the advantage of high utilization of the stator core slots by the rectified high rectification efficiency.

(2) Fundamental wave secondary winding. In order to establish a self-excited voltage generator smoothly, reliably, harmonic excitation phase synchronous generator in addition to the secondary windings in the stator slots must be embedded with the third harmonic of the fundamental secondary windings. The shape of the fundamental winding is the same as that of the main winding, and its pitch is also the same as that of the main winding. Therefore, the fundamental winding is wound by the winding of the main winding, but the number of turns is small.

2. Working principle

Harmonic excitation phase AC generator principle circuit shown in Figure 3-21. In the synchronous generator main magnetic field pole core, inevitably contains a series of odd harmonic components, especially in the stator and rotor salient pole generator air gap uniform main magnetic field structure, the content of third harmonic is maximum Harmonic components, the third harmonic excitation generator is the use of this third harmonic magnetic field.

When the load, as long as the generator rotor pole iron core has a residual magnetic field, will contain a third harmonic component of residual magnetization in a magnetic field. When the rotor rotates, the third harmonic winding induces a third harmonic voltage, which is rectified by the rectifier bridge group and supplied to the rotor pole winding. As the generator excitation power source, the generator establishes no-load voltage. Adjusting the magnetic field rheostat, the generator may be in the amount of load voltage setting value.

During the load, there is a current in the stator winding of the generator, which forms an armature reaction magnetic field. The reaction magnetic field also contains the third harmonic component in the reaction magnetic field of the direct axis and the cross-axis armature (the two winding positions are different by 90° electrical angle) . If the load power factor is lagging and the rotor pole pole arc coefficient ap>2/3 , the third harmonic component in the armature reaction magnetic field plays a role in assisting the third harmonic component in the rotor main magnetic field to make the generator gas The third harmonic magnetic field in the integrated magnetic field is enhanced, and the voltage induced by the third harmonic winding is correspondingly increased, so that the excitation voltage of the rotor pole winding rises, the excitation current increases, and the generator terminal voltage is stabilized. This generator structure and circuit are very simple and low in manufacturing cost. The voltage regulation rate can only reach 7%, but it can basically meet the power requirements of general power equipment and electric heating equipment. For high voltage accuracy requirements, an automatic voltage regulator must be provided.