Armature Reaction in a Synchronous Generator

Introduction:
In a synchronous generator, armature reaction refers to the magnetic field produced by the armature windings that affects the main magnetic field produced by the field windings. This interaction can have different effects on the generator's performance, depending on the power factor of the load.

Armature Reaction at Zero Power Factor Lagging:
When a synchronous generator operates at zero power factor lagging, the load is purely reactive, and the armature current lags the generator terminal voltage by 90 degrees. In this condition, the armature reaction has a demagnetizing effect on the main magnetic field produced by the field windings.

Demagnetizing Effect:
The armature current in a synchronous generator produces its own magnetic field, which interacts with the main magnetic field. At zero power factor lagging, the armature current lags the generator terminal voltage by 90 degrees. This results in the armature magnetic field being out of phase with the main magnetic field.

The armature magnetic field opposes the main magnetic field, weakening it. This demagnetizing effect reduces the overall flux in the generator, which leads to a decrease in the generator's terminal voltage. The demagnetizing effect of the armature reaction is more pronounced at low power factors, such as zero power factor lagging.

Magnetizing Effect:
In contrast, at unity power factor (purely resistive load), the armature current is in phase with the generator terminal voltage. This results in the armature magnetic field reinforcing the main magnetic field, increasing the overall flux in the generator. Therefore, at unity power factor, the armature reaction has a magnetizing effect.

Cross-Magnetizing Effect:
Cross-magnetizing effect refers to the component of armature reaction that is perpendicular to the main magnetic field. At zero power factor lagging, the armature current lags the generator terminal voltage by 90 degrees, resulting in a cross-magnetizing effect. This effect can cause additional distortion of the generator's magnetic field and introduce harmonics in the output voltage waveform.

Conclusion:
In summary, when a synchronous generator operates at zero power factor lagging, the armature reaction has a demagnetizing effect on the main magnetic field. This demagnetizing effect reduces the flux in the generator and decreases the terminal voltage. Additionally, there is also a cross-magnetizing effect that can cause distortion and harmonics in the output voltage waveform.