w - angular velocity.

f - frequency (number of cycles per second, expressed in Hz).

P - number of poles (= N + S poles. ).

P/2 - number of pole pairs. Above generator example has two poles and one pole pair.

Ns - number of revolutions per second

Nm - number of revolutions per minute

Nm=60*Ns.

w=2Pi*f = (P/2) * N * 2Pi * 1/sec

f=(P/2)*N/sec

f=(P/2)*Ns

**f=(P/2)*Nm/60=P*N/120**

**f=P*Nm/120**