For a P-pole machine, the relation between electrical and mechanical degrees is

(a) 
(b) 
(c) 
(d) 

Answer: (d) 

 

Explanation:

CONCEPT: Mechanical and Electrical Angles

1. Mechanical angle ():
• Represents the actual physical rotation of the rotor or shaft.
2. Electrical angle ():
• Represents the angular position related to one cycle of induced EMF or current.
3. Poles (P):
• Total number of magnetic poles (north + south).
4. Pole pairs:
• Number of pole pairs = .

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Relationship Between Mechanical Rotation and Electrical Cycles

5. In one full mechanical revolution (360° mechanical):
• The rotor passes through P/2 pole pairs.
6. Each pole pair produces:
• One complete electrical cycle (360° electrical).
7. Therefore:
• One mechanical rotation corresponds to P/2 electrical cycles.

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Formula Derivation

8. Since the electrical angle increases P/2 times faster than the mechanical angle:

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EXPLANATION

9. Electrical quantities such as EMF and current complete one full cycle for each pole pair encountered.
10. Hence, the electrical angle is scaled by the number of pole pairs relative to the mechanical angle.
11. This relationship is fundamental in the analysis of AC machines, including:

• Alternators
• Synchronous motors
• Induction motors

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Final Answer

✅ Correct option: (d)

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✔️ Key One-Line Exam Statement

Electrical angle equals mechanical angle multiplied by the number of pole pairs.