Armature Reaction in an Alternator

Armature reaction is the effect of the armature flux on the main field flux in an alternator. The armature flux is generated in the armature winding when an alternating current flows through it. This flux interacts with the main field flux, which is generated by the field winding on the rotor, and thereby alters the distribution of the main field flux in the air gap. The armature reaction can be either demagnetizing or magnetizing depending on the power factor of the load.

Armature Reaction and Power Factor

The power factor of a load is the ratio of the real power (or active power) to the apparent power (or total power). It is a measure of the efficiency of the load in utilizing the supplied power. The power factor can be lagging, leading or unity depending on the nature of the load.

- Lagging power factor: When the load is inductive, the power factor is lagging. This means that the load consumes reactive power, which lags behind the real power. The phase angle between the voltage and current is such that the current lags behind the voltage.
- Leading power factor: When the load is capacitive, the power factor is leading. This means that the load generates reactive power, which leads the real power. The phase angle between the voltage and current is such that the current leads the voltage.
- Unity power factor: When the load is resistive, the power factor is unity. This means that the load consumes only real power and there is no reactive power. The phase angle between the voltage and current is zero.

Effect of Power Factor on Armature Reaction

The effect of the armature reaction on the main field flux depends on the power factor of the load. When the load power factor is unity, the armature reaction is negligible because there is no reactive power. However, when the load power factor is lagging or leading, the armature reaction becomes significant.

- Lagging power factor: When the load power factor is lagging, the armature reaction is demagnetizing. This means that the armature flux opposes the main field flux and reduces the flux density in the air gap. The demagnetizing effect is maximum at a lagging power factor of 0.8.
- Leading power factor: When the load power factor is leading, the armature reaction is magnetizing. This means that the armature flux reinforces the main field flux and increases the flux density in the air gap. The magnetizing effect is maximum at a leading power factor of 0.8.

Conclusion

In an alternator, the armature reaction can be either demagnetizing or magnetizing depending on the power factor of the load. When the load power factor is unity, the armature reaction is negligible. However, when the load power factor is lagging or leading, the armature reaction becomes significant. At a lagging power factor of 0.8, the demagnetizing effect is maximum, whereas at a leading power factor of 0.8, the magnetizing effect is maximum.