A power station alternator (a.c. generator) is made of 3 sets of stationary coils (stator) at 120° to each other and a rotor - an electromagnet that spins in the middle of the coil. The electromagnet is connected to a d.c. supply and induced an alternating e.m.f. in each of the coils. The three e.m.fs are out of phase with each other by 120°.