In a drum type dc armature winding the back pitch and front pitch in terms of the coil-sides must be

(a) even and odd respectively.
(b) odd and even respectively.
(c) both even.
(d) both odd.

Answer: (d) both odd.

Explanation:

CONCEPT: Pitch in DC Armature Windings

1. In DC machines, the armature winding must be balanced for:
• Proper commutation
• Smooth current collection
• Uniform EMF distribution
2. This balance depends strongly on the choice of pitches.

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Definitions

Back Pitch (  )

3. Back pitch is:
• The distance between the top and bottom coil sides of the same coil
• Measured around the back of the armature
• Expressed in coil sides or slots

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Front Pitch (  )

4. Front pitch is:
• The distance between the two coil sides connected to the same commutator segment
• Measured around the front of the armature
• Also expressed in coil sides or slots

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EXPLANATION

5. For a practical drum-type DC winding:
• The winding must return smoothly to the commutator
• The coil connections must be symmetrical
6. To satisfy these conditions:
• The average pitch must be an integer

7. For  to be an integer:
• Both  and  must be odd numbers
8. Also:
• The difference  must be an even number (commonly 2 for simplex windings)
9. Example:

This gives a balanced and practical winding.

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Special Note on Wave Winding

10. In simplex wave winding:
• Both back pitch and front pitch are always odd
• Both are of the same sign (progressive or retrogressive)
11. This is essential for the wave progression around the armature.

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FINAL CONCLUSION

12. In a drum-type DC armature winding, for practical and balanced operation:

13. Hence, the correct answer is:

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Correct Answer

✅ Option (d): Both odd

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✔️ Key One-Line Exam Statement

For a balanced drum-type DC armature winding, both back pitch and front pitch must be odd numbers.