In an electromechanical energy conversion device, the developed torque depends upon

(a) stator field strength and torque angle.
(b) stator field and rotor field strengths.
(c) stator field and rotor field strengths and the torque angle.
(d) stator field strength only.

Answer: (c) stator field and rotor field strengths and the torque angle.

Explanation:

CONCEPT: Electromechanical Energy Conversion

1. An electromechanical energy conversion device converts:
• Electrical energy → Mechanical energy (motor), or
• Mechanical energy → Electrical energy (generator).
2. The conversion takes place through a coupling medium, generally a magnetic field.
3. Magnetic field is preferred because its energy storage capability is higher than that of the electric field.
4. The energy conversion process is reversible.

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Torque Production Principle

5. Electromagnetic torque is produced due to the interaction of magnetic fields.
6. In rotating machines, torque arises from the interaction between:
• The stator magnetic field
• The rotor magnetic field

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Factors Affecting Developed Torque

(a) Stator Field Strength

7. A stronger stator field increases the force acting on the rotor conductors or poles.
8. Hence, torque increases with stator field strength.

(b) Rotor Field Strength

9. A stronger rotor field increases the interaction with the stator field.
10. Hence, torque is directly proportional to rotor field strength.

(c) Torque Angle (δ)

11. The torque angle (δ) is the angle between the stator and rotor magnetic axes.
12. Torque depends on the sine of this angle:

13. Maximum torque occurs when sin δ is maximum.

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EXPLANATION

14. Since torque is produced due to the interaction of stator and rotor magnetic fields, both field strengths directly influence torque.
15. The relative alignment of these fields (torque angle) determines how effectively the interaction produces torque.
16. Therefore, torque depends on:

• Stator field strength
• Rotor field strength
• Torque angle (δ)

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Final Answer

✅ Correct option: (c)
Stator field strength, rotor field strength, and torque angle

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✔️ Key One-Line Exam Statement

In electromechanical energy conversion devices, torque is proportional to stator field strength, rotor field strength, and sin δ.