Armature Reaction in DC Generator

Armature reaction is a phenomenon that occurs in DC generators due to the interaction of armature flux with the main field flux. This interaction leads to a change in the distribution of the magnetic field in the air gap, which affects the performance of the generator. The armature reaction can be either demagnetizing or cross-magnetizing, depending on the direction of the armature current and the polarity of the main field.

Causes of Armature Reaction

The main causes of armature reaction in DC generator are:

1. Armature Current: When the armature current flows through the armature winding, it produces its own magnetic field, which interacts with the main field to create the armature reaction.

2. Field Current: The field current also plays a role in armature reaction, as it affects the distribution of the magnetic field in the air gap.

3. Commutation: Commutation is the process of converting the AC voltage induced in the armature winding into DC voltage. During this process, there is a brief moment when the brushes are in contact with both the outgoing and incoming commutator segments, which causes a short-circuit current to flow in the armature winding. This short-circuit current interacts with the main field to create the armature reaction.

Role of Field and Armature Current

Both the field and armature current play a role in armature reaction, as they affect the distribution of the magnetic field in the air gap. The field current is responsible for creating the main field in the generator, which interacts with the armature current to create the armature reaction. The armature current, on the other hand, produces its own magnetic field, which interacts with the main field to create the armature reaction.

Therefore, the correct answer to the question is option 'B' - Field and Armature Current.