Given Ns as synchronous speed and s as slip, the operational speed of an induction motor will be___________?
Show answer Hide answer
Answer: C. (l-s)Ns
Explanation
The operational speed of an induction motor is always slightly lower than the theoretical synchronous speed. Slip represents the fractional difference between synchronous speed and the actual rotor mechanical operating speed. Multiplying synchronous speed by one minus the slip factor directly yields the true mechanical rotor speed. Synchronous speed depends entirely on the supply frequency and the number of stator magnetic poles. Slip is dimensionless and measures the relative speed difference required to induce rotor currents. Without a relative speed difference between stator field and rotor, no electromagnetic torque could be generated.
Calculating actual rotor speed is crucial for determining motor efficiency in industrial manufacturing applications. Electrical engineers use this mathematical relationship to monitor performance and predict slip under varying loads. Knowing operational speed helps in selecting appropriate gearboxes for pumps, fans, and conveyor systems. Option A represents synchronous speed, which only occurs if the rotor rotates without any mechanical load. Option B incorrectly scales synchronous speed by slip alone, ignoring the fundamental speed reduction mechanics. Option D presents a mathematically invalid formula that bears no resemblance to standard induction motor equations.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
Related questions
Q1. By what means can the starting torque of a three-phase induction motor be enhanced__________?
Show answer Hide answer
Answer: C. both A. and (b)
The starting torque of an induction motor depends directly on rotor resistance and reactance values. Increasing rotor resistance improves the starting torque by optimizing the phase angle of current. Ensuring adequate cu...
Q2. Introducing external resistance into the stator of an induction motor___________?
Show answer Hide answer
Answer: B. decreases the starting torque
Adding external resistance directly into the stator circuit increases total circuit impedance. Higher impedance limits the electrical current flowing into the motor windings during startup. Reduced stator current signifi...
Q3. The phenomenon known as cogging is typically linked with___________?
Show answer Hide answer
Answer: D. induction motors
Cogging occurs when the number of stator slots interacts unfavorably with the number of rotor slots. This magnetic locking phenomenon prevents the induction motor from reaching its normal operating rotational speed. The...
Q4. How can the transformation ratio value of an induction motor be evaluated__________?
Show answer Hide answer
Answer: B. short-circuit test only
The short-circuit test provides necessary voltage and current measurements to evaluate leakage reactances accurately. During this blocked-rotor test, the rotor is held stationary while a reduced voltage is applied safely...
Q5. What is the characteristic profile of the torque-slip curve for an induction motor__________?
Show answer Hide answer
Answer: C. rectangular parabola
Mathematical analysis of equivalent circuits reveals the hyperbolic shape of the motor torque curve. In the normal operating region, the torque-slip relationship resembles a rectangular parabola curve. This graphical cur...
Q6. Under no-load conditions, the power factor of an induction motor tends to be close to_____________?
Show answer Hide answer
Answer: A. 0.2 lagging
Under no-load conditions, the induction motor draws a very large magnetizing current from the supply. This high reactive current component creates the necessary magnetic field while contributing very little active power....