Page 764 - Basic Electrical Engineering

Let the rpm of the rotor be N . Let ϕ be the flux per pole. For a two-pole
s
machine, the flux cut by a conductor (coil side) in one revolution is 2 ϕ W. If

P is the number of poles, then flux cut by a conductor in one revolution of the
rotor is Pϕ webers. The rotor makes N revolutions per minute. In terms of
s

seconds, the rotor makes resolutions. Thus, the time taken by the rotor to

make one revolution is seconds. (Since N is the rpm, or is the

revolutions per second.)

Average value of the induced EMF = flux cut/second

If the number of turns per phase is T, then the total number of conductors
Z will be 2T.

Hence, Average EMF induced in each phase

If, f is the frequency of the induced EMF, the relationship between, f, P,

and N is given by
S

From (i) and (ii)

For a sinusoidal wave, the ratio of the rms value to the average value is
called the form factor which is equal to 1.11.