Consider the following statements regarding Induction Motor Torque:1.The maximum torque developed by an induction motor is independent of rotor resistance under constant supply conditions.2.Increasing rotor resistance improves the starting torque of a slip-ring induction motor.3.The slip corresponding to maximum torque is directly proportional to rotor resistance.4.The electromagnetic torque becomes zero when the rotor reaches synchronous speed.Which of the above statements is/are correct?
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For a given supply, the value of maximum torque is approximately independent of rotor resistance, while the slip at which it occurs is proportional to rotor resistance. Adding rotor resistance in a slip-ring motor can improve starting torque and shift maximum torque toward standstill. Key relation: s_max≈R₂/X₂ (referred form, simplified); T∝sR₂/(R₂²+(sX₂)²).
Exam focus: Rotor resistance shifts the torque-slip curve horizontally; it does not materially raise Tmax. Common trap: Maximum torque does not occur at synchronous speed because slip is zero there.
Correct Answer: D - All of the above Quick Concept Explanation For a given supply, the value of maximum torque is approximately independent of rotor resistance, while the slip at which it occurs is proportional to rotor resistance. Adding rotor resistance in a slip-ring motor can improve starting torque and shift maximum torque toward standstill. Key relation: s_max≈R₂/X₂ (referred form, simplified); T∝sR₂/(R₂²+(sX₂)²).Exam focus: Rotor resistance shifts the torque-slip curve horizontally; it does not materially raise Tmax. Common trap: Maximum torque does not occur at synchronous speed because slip is zero there. Statement-wise Verification Statement 1 - Correct.The maximum torque developed…
Correct Answer: D - All of the above
Quick Concept Explanation
For a given supply, the value of maximum torque is approximately independent of rotor resistance, while the slip at which it occurs is proportional to rotor resistance. Adding rotor resistance in a slip-ring motor can improve starting torque and shift maximum torque toward standstill. Key relation: s_max≈R₂/X₂ (referred form, simplified); T∝sR₂/(R₂²+(sX₂)²).
Exam focus: Rotor resistance shifts the torque-slip curve horizontally; it does not materially raise Tmax. Common trap: Maximum torque does not occur at synchronous speed because slip is zero there.
Statement-wise Verification
Statement 1 - Correct. The maximum torque developed by an induction motor is independent of rotor resistance under constant supply conditions. Induction-motor torque depends on slip and rotor resistance.
Statement 2 - Correct. Increasing rotor resistance improves the starting torque of a slip-ring induction motor. Adding rotor resistance in a slip-ring motor can improve starting torque and shift maximum torque toward standstill.
Statement 3 - Correct. The slip corresponding to maximum torque is directly proportional to rotor resistance. For a given supply, the value of maximum torque is approximately independent of rotor resistance, while the slip at which it occurs is proportional to rotor resistance.
Statement 4 - Correct. The electromagnetic torque becomes zero when the rotor reaches synchronous speed. Induction-motor torque depends on slip and rotor resistance.
Core Concept
Induction-motor torque depends on slip and rotor resistance. For a given supply, the value of maximum torque is approximately independent of rotor resistance, while the slip at which it occurs is proportional to rotor resistance. Adding rotor resistance in a slip-ring motor can improve starting torque and shift maximum torque toward standstill.
Option A is incorrect because it omits correct statement(s) 1, 2. Option B is incorrect because it omits correct statement(s) 2, 4. Option C is incorrect because it omits correct statement(s) 1, 4.
Exam Shortcut / Approach
Rotor resistance shifts the torque-slip curve horizontally; it does not materially raise Tmax.
Common Mistake
Maximum torque does not occur at synchronous speed because slip is zero there.
Quick Revision
Maximum Torque and Rotor Resistance is linked with Torque-Slip Characteristics, Induction Motors and Electrical Machines. Rotor resistance shifts the torque-slip curve horizontally; it does not materially raise Tmax.
Quick Trick
Rotor resistance shifts the torque-slip curve horizontally; it does not materially raise Tmax.
Why Other Options Are Wrong
Option A is incorrect because it omits correct statement(s) 1, 2. Option B is incorrect because it omits correct statement(s) 2, 4. Option C is incorrect because it omits correct statement(s) 1, 4.
Common Mistake
Maximum torque does not occur at synchronous speed because slip is zero there.
Exam Tip
Rotor resistance shifts the torque-slip curve horizontally; it does not materially raise Tmax.
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