Function of Interpoles in a DC Machine

Interpoles are small auxiliary poles placed between the main poles of a DC machine. They are connected in series with the armature winding and are wound with a few turns of small gauge wire. The main function of interpoles is to improve commutation in a DC machine.

Improving Commutation

1. Definition of Commutation: Commutation is the process of changing the direction of current in a coil as it rotates within a magnetic field. In a DC machine, commutation ensures that the current flowing through the armature coil is always in the same direction relative to the field poles. A good commutation is essential for the proper operation of a DC machine.

2. Role of Interpoles: Interpoles help in achieving better commutation by neutralizing the cross-magnetizing effect of armature reaction. When the armature current flows, it produces a flux that opposes the main field flux, resulting in armature reaction. This armature reaction distorts the main field flux and causes poor commutation.

3. Neutralizing Armature Reaction: The interpoles are connected in series with the armature winding and produce a flux that is opposite to the armature reaction. This neutralizes the armature reaction and helps in maintaining a uniform magnetic field around the armature. As a result, the commutation process becomes smoother and more efficient.

4. Compensation for Magnetic Field Variation: Another important function of interpoles is to compensate for the magnetic field variation caused by load changes. When the load on the DC machine changes, the armature current also changes, resulting in variations in the magnetic field. This can lead to poor commutation. However, the interpoles produce a magnetic field that adjusts itself to compensate for these variations and ensures good commutation under different load conditions.

5. Reduction of Sparking: Improved commutation achieved by interpoles reduces the sparking at the brushes. Sparking causes excessive wear on the brushes and commutator, leading to reduced machine efficiency and increased maintenance requirements.

Conclusion

In summary, interpoles play a crucial role in improving commutation in a DC machine. They neutralize the armature reaction, compensate for magnetic field variation, and reduce sparking, ensuring efficient and reliable operation of the machine.