A Brief Introduction to Armature Reaction of Synchronous Motors
When a synchronous generator outputs load, the magnetic field generated by the current in the armature winding will act on the main magnetic field. This is the armature reaction of the synchronous generator.
1) When the generator outputs a capacitive load, the direction of the armature reaction magnetic field is the same as that of the main magnetic field, which will have a magnetizing effect on the main magnetic field;
2) When the generator outputs an inductive load, the direction of the armature reaction magnetic field is opposite to that of the main magnetic field, which will have a demagnetizing effect on the main magnetic field;
3) When the generator outputs a resistive load, the armature reaction magnetic field is perpendicular to the main magnetic field. At the front tip of the main magnetic pole, it is opposite to the direction of the main magnetic field and has a demagnetizing effect on the main magnetic field. At the rear tip of the main magnetic pole, it is in the same direction as the main magnetic field and has a magnetizing effect on the main magnetic field. Since the motor operates in a state where the magnetic circuit is close to saturation, the magnetizing effect is less than the demagnetizing effect, and the overall magnetic field is slightly reduced.
Armature reaction conditions of synchronous motors
When a synchronous generator is outputting power, current flows through the armature, which generates a magnetic field. This magnetic field interacts with the main magnetic field, resulting in armature reaction. When the stator is under current, there is no armature reaction under no-load conditions.
Armature reaction effect
The typical armature reaction effects are mainly of the following three types:
① Cross-axis armature reaction occurs when E0 and Ia are in phase (if the influence of armature winding reactance is ignored, the generator is equivalent to a purely resistive load).
② Direct-axis demagnetizing armature reaction occurs when Ia lags behind E090° (at which point the generator is carrying a purely inductive load).
③ The direct-axis magnetizing armature reaction occurs when Ia leads E090° (at which point the generator is carrying a purely capacitive load).
Physical meaning of synchronous reactance
Synchronous reactance is the sum of the stator leakage reactance and the armature reaction reactance of a synchronous motor. It represents the effect of the armature reaction magnetic field and leakage magnetic field on each phase circuit when the synchronous motor is operating symmetrically and stably.
Difference between armature reaction reactance and synchronization reactance
Armature reaction reactance: When a load is applied to a synchronous generator, a circuit is formed, and a current is generated in the stator winding, which is the armature winding. This current also generates a magnetomotive force, called armature magnetomotive force. This armature magnetomotive force affects the excitation magnetomotive force, which is called armature reaction.
The results of armature reaction are divided into three categories depending on the type of load.
1) If it is a resistive load, the combined magnetomotive force of the armature magnetomotive force and the excitation magnetomotive force will increase, and the combined magnetomotive force will be slightly larger.
2) If it is an inductive load, the combined magnetomotive force of the armature magnetomotive force and the excitation magnetomotive force will be much smaller, and the combined magnetomotive force will be smaller.
3) If it is a capacitive load, the combined magnetomotive force of the armature magnetomotive force and the excitation magnetomotive force will increase. The combined magnetomotive force becomes larger.
Armature reaction reactance reflects the degree to which the armature reaction magnetomotive force influences the excitation magnetomotive force. Armature reaction reactance is an external characteristic of armature reaction.
Synchronization reactance includes armature reaction reactance, as well as stator leakage reactance. This is the relationship between synchronization reactance and armature reaction reactance—a subordinate relationship.
