EASA / CAR Part-66 · Module 3 · 3.17 AC Generators · Cat B1/B2

Three-Phase AC

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.

Phase A
,
Phase B
,
Phase C
,
A + B + C
,

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.