The difference between the speed of the revolving field (Ns) and the rotor speed (N), expressed as a percentag

Question

The difference between the speed of the revolving field (Ns) and the rotor speed (N), expressed as a percentage of synchronous speed (Ns) is called __________

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Option C: slip

Explanation & Concepts:
The correct answer is C, slip, which refers to the difference between the speed of the revolving magnetic field (synchronous speed, $N_s$) and the rotor speed ($N$), expressed as a percentage of synchronous speed.

Working Principle: In induction motors, slip occurs due to the rotor not rotating at synchronous speed. This difference allows for relative motion between the rotor and the rotating magnetic field, inducing currents in the rotor and creating torque, essential for motor operation.

Key Formulas: $Slip = \frac{N_s - N}{N_s} \times 100 \%$ — represents the slip as a percentage of synchronous speed.

Key Points: Slip is crucial for the induction motor's operation, enabling torque production.; Higher slip indicates more load on the motor, while lower slip suggests light loading.

Advantages: Provides necessary torque for induction motor operation; Enables speed control under varying load conditions

Disadvantages: Higher slip can lead to increased losses and reduced efficiency; Excessive slip may result in overheating

Applications: Used in various industrial applications where variable loads are common; Found in fans, pumps, and conveyor systems

Additional Info: Standard value for slip in industrial motors is generally 2-6%.. Option A refers to slip speed, which is not the term used here for percentage difference.

Answer: C is correct — slip represents the percentage difference between synchronous speed and rotor speed.

Exam Tip: Understanding slip is essential for analyzing performance issues in AC machines.

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Option A: slip speed

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Option B: rotor rmf speed wrt stator

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Option D: Speed at which rotor shaft slip from bearing

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