Electrical Engineering XYZ MCQs

At stand still condition the value of slip is:

- 0
- 1
- Finite value
- Infinite value

Correct answer: 2. 1

Explanation: Slip in an induction motor is defined as the difference between the synchronous speed (N_{s}) of the magnetic field in the stator and the actual speed (N_{r}) of the rotor, expressed as a fraction of the synchronous speed. It is usually given by the formula:

s = (Ns – Nr)/Ns

Where:

- s is the slip
- N
_{s} is the synchronous speed - N
_{r }is the rotor speed

At standstill condition, the rotor speed 𝑁𝑟*N**r* is 0 because the rotor is not moving. Therefore, if we plug this into the slip formula, we get:

𝑠 = (𝑁_{𝑠}−0)/𝑁_{𝑠}=𝑁𝑠 = 𝑁𝑠/𝑁𝑠 = 1

Thus, at standstill, the slip 𝑠 is 1. This means the rotor is stationary relative to the rotating magnetic field produced by the stator, and it needs to catch up to the field’s rotational speed to start turning. This is typical when the motor is just starting up. As the motor reaches closer to its operating speed, the slip decreases but remains a positive finite value less than 1 during normal operation.