1. SEE 3433 ELECTRICAL MACHINES Interpoles in DC machines

2. Current in a conductor changes direction as the conductor moves between the poles Why do we need interpoles (or commutator poles) ?

3. Current in a conductor changes direction as the conductor moves between the poles Why do we need interpoles (or commutator poles) ?

4. Current in a conductor changes direction as the conductor moves between the poles Why do we need interpoles (or commutator poles) ? Ideal situation – current changes linearly

5. Actual case: Why do we need interpoles (or commutator poles) ? 1. Inductance in a coil delays the changes of current in that coil 2. Non-zero flux between poles induced voltage (reactance voltage) which further delays the changes

7. Non-zero flux between the poles

8. Why do we need interpoles (or commutator poles) ? Ideal situation – current changes linearlyActual situation – delay in current changes

9. Why do we need interpoles (or commutator poles) ? Flux produced by interpoles will cancel the flux produced by armature reaction