An alternating current generator consists of a rectangular coil that spins within a magnetic field, inducing an electromotive force (EMF) that varies with the cosine of the angle between the coil and magnetic field. Power station alternators have three coil sets spaced 120 degrees apart, each producing an alternating EMF 120 degrees out of phase with the others. The electromagnet at the center spins rather than the coils. A back EMF is induced in a spinning electric motor coil as the flux linkage through it changes, opposing the applied voltage and wasting power through circuit resistance.

1. Alternating current generator
By S, J and S

2. What is it?
• A simple AC generator consist of:
– A rectangular coil.
– A magnetic field.
• The coil spins in the magnetic field.

4. Induced EMF
• When the coil is perpendicular to the B-
field induced EMF is at a maximum.
• When the coil is parallel to B-field induced
EMF is 0
• Because ε=BANωcosωt

6. Power Station Alternators!
• In a power station 3 sets of
coils are used at 120° from
each other.
• Each produce an
alternating emf 120° out of
phase from one another.
• The coils don’t spin the
electromagnet (in the
middle) does.

8. Back EMF
• An EMF is induced in the spinning coil of an
electric motor because the flux linkage
through the coil changes.
• The induced EMF is referred to as a back
EMF because it’s opposed to the p.d.
• Electric power supplied by the source (IV) =
electrical power transferred to the mechanical
power (Iε) + electrical power wasted due to
circuit resistance (I²R).

9. Fin

10. Fin