With reference to the synchronous motor, state true or false for following statements.

1. The percentage slip is always zero.

2. The speed regulation is always zero.

Concept: 

With reference to Synchronous Motor:

Statement 1: The Percentage slip is always zero

A synchronous motor rotates due to the interlocking of stator R.M.F. poles and rotor poles. Due to this Interlocking, the rotor always rotates at a synchronous speed.

Slip (s): The difference between the rotor speed (N) and the rotating magnetic flux speed (Ns) is called slip.

s = Ns - N

fractional slip, \(s = \frac{{{N_s}\;-\;N}}{{{N_s}}}\) 

The motor slip is usually expressed as a percentage of synchronous speed (NS).

Percentage slip, \(\% \;s = \left[ {\frac{{{N_s}\;-\;N}}{{{N_s}}}} \right] \times 100\)

At synchronous speed: N = Ns

Percentage Slip, \(\%\ s = [\frac{{{N_s}\;-\;{N_s}}}{{{N_s}}} ]\times100= 0\)

Statement 2: The speed regulation is always zero

Speed regulation of induction motor is the ratio of the change in speed from no load to full load to the full load speed.

Speed regulation = (No load speed – Full load speed) / (Full load speed)

Synchronous motor running at a constant synchronous speed.

Therefore there is no speed loss, so the speed regulation of the synchronous motor is zero.