(a) facilitate cooling of rotor
(b) balance the rotor dynamically
(c) eliminate noise
(d) none of these
Answer: (a) facilitate cooling of rotor
Explanation:
📖 Detailed Solution
🔹 During operation, electrical and mechanical losses generate heat inside the motor.
🔹 Excessive heat can damage insulation, windings, and bearings.
🔹 The blades are designed as part of the rotor structure or end rings.
🔹 They act as a centrifugal fan.
🔹 When the rotor rotates, air is circulated inside the motor.
🔹 This air flow removes heat from internal components.
🔹 Proper cooling improves efficiency and increases motor life.
👉 Therefore, the primary function of rotor blades is cooling.
⚙️ Main Parts Related to Cooling System are:
✔️ Rotor Blades / Fan
✔️ Cooling Ducts
✔️ Ventilation Openings
✔️ Stator Frame
✔️ Housing
🌬️ Cooling Mechanism in Squirrel Cage Motor:
🔹 Rotor-mounted blades rotate with the shaft.
🔹 Air is drawn from one side and expelled from the other.
🔹 Heat is transferred to surrounding air.
🔹 Continuous ventilation is maintained.
🔹 Prevents overheating under load conditions.
❌ Why Other Options are Incorrect
(b) Balance the rotor dynamically ❌
🔹 Rotor is balanced during manufacturing.
🔹 Blades are not meant for balancing.
🔹 Their main function is cooling.
(c) Eliminate noise ❌
🔹 Noise reduction is mainly done by skewing rotor slots.
🔹 Blades do not reduce noise.
🔹 Airflow may even increase noise.
(d) None of these ❌
🔹 Incorrect because option (a) is correct.
📌 Key Exam Notes
⭐ Blade Function → Cooling
⭐ Cooling Method → Forced Air Ventilation
⭐ Purpose → Heat Dissipation
⭐ Benefit → Long Motor Life
⭐ Efficiency → Improved
📝 Final Summary
📍 The blades on a squirrel cage motor rotor:
✔️ Circulate air
✔️ Remove internal heat
✔️ Protect windings
✔️ Improve durability
👉 Hence, Option a is Correct.