SSE JE Electrical Engineering 10 Dec 2020 Papers

The difference between the rotor speed (N) and the rotating magnetic flux speed $\left({\mathrm{N}}_{\mathrm{s}}\right)$ is called slip.
The induction motor slip is usually expressed as a percentage of synchronous speed $\left({\mathrm{N}}_{\mathrm{s}}\right)$ and is represented by symbol s.
Mathematically, Percentage slip, $\%\mathit{s}=\left[\frac{{\mathrm{N}}_{\mathrm{s}}-\mathrm{N}}{{\mathrm{N}}_{\mathrm{s}}}\right]\times 100$
Or fractional slip, $\mathrm{s}=\frac{{\mathrm{N}}_{\mathrm{s}}-\mathrm{N}}{{\mathrm{N}}_{\mathrm{s}}}$
At start, $\mathrm{N}=0$, therefore, $\mathrm{Slip},\mathrm{s}=\frac{{\mathrm{N}}_{\mathrm{s}}-0}{{\mathrm{N}}_{\mathrm{s}}}=1$
At synchronous speed, Slip, $\mathrm{S}=\frac{{\mathrm{N}}_{\mathrm{s}}-{\mathrm{N}}_{\mathrm{s}}}{{\mathrm{N}}_{\mathrm{s}}}=0$