Mechanical and Electrical Angle

We have seen that for 2 pole alternator, one mechanical revolution corresponding to one electrical cycle of an induced emf Now consider 4 pole alternator i.e. the field winding is designed to produce 4 poles. Due to 4 poles, the magnetic axis exists diagonally as shown in figure-

    Now in position 1 of the conductor, the velocity component is parallel to the flux lines while in position 2, there is the gathering of flux lines and entire velocity component is perpendicular to the flux lines.

figure-

So at position 1, the induced emf in the conductor is zero while at position 2, it is maximum. Similarly, as conductor rotates, the induced emf will be maximum at positions 4, 6 and 8 and will be minimum at positions 3, 5 and 7. So during one complete revolution of the conductor, inducted emf will experience four times maxima, twice in either direction and four times zero. This is because of the distribution of flux lines due to the existence of four poles.

So if we plot the nature of the induced emf, for one revolution of the conductor, we get the two electrical cycles of the induced emf, as shown in figure-

So for a  four-pole alternator, we can write,

360⁰ electrical = 720⁰ mechanical

From this, we can establish the general relation between degrees mechanical and degrees electrical as.

360⁰ electrical = 360⁰  x  P/2 mechanical

P= No. of Poles

i.e.

1⁰ electrical = (P/2)⁰ mechanical

I hope that this article will be informative for you all.

Thanks and Regards

Er. Abhishek Srivastava