EASA Module 3 · AC Generation
Aircraft power is three-phase: three separate windings 120° apart. See the three sine waves and their rotating phasors — and note their instantaneous sum is always zero.
Each phase peaks 120° (one-third of a cycle) after the previous one. At every instant the three add up to zero, which is why a balanced three-phase system needs no return in the neutral. Three-phase gives smoother power and lighter generators than single-phase.