For a three-phase induction motor slip at No Load ÷ slip at Full Load

• A. Always less than one
• B. Always equal to one
• C. Always equal to zero
• D. Always less than one

Answer: (D)

In terms of slip, the actual speed of the motor (N) can be expressed as
N = Ns(1 − s)
At start, the motor is at rest and hence its speed N is zero.
s = 1 ( start)
This is the maximum value of slip s possible for the induction motor which occurs at start. While s = 0 gives us N = N. which is not possible for an induction motor. So slip of the induction motor cannot be zero under any circumstances.
Practically motor operates in the slip range of 0.01 to 0.05 i.e. 1 % to 5 %. The slip corresponding to the full load speed of the motor is called full load slip.