Question

Dummy coils may be needed in a DC wave winding _______.

• A. to achieve mechanical balance of armature
• B. to achieve electrical balance of parallel paths
• C. to avoid use of equalizer rings
• D. to achieve good commutation

Hint:

Dummy coils = Mechanical balance only. Not connected to commutator or circuit!

Answer 1

The Correct Option is A

Step 1: What are dummy coils?
Dummy coils are non-functional coils inserted in the armature slots to maintain physical symmetry of winding.
Step 2: Why are they used?
In wave windings, due to constraints on number of conductors (must fit winding equations), sometimes we can’t use all slots.
To keep mechanical balance: - Dummy coils are inserted without connecting them electrically.
Step 3: Key point.
These coils do not carry current or contribute to EMF generation — only serve structural/mechanical purpose.
Conclusion: Dummy coils are required for mechanical symmetry of the armature.