Decompose unbalanced three-phase phasors into positive-, negative-, and zero-sequence components (Fortescue's theorem). Used for fault analysis per IEEE Std 141 (Red Book).
Units can be V, kV, A, or per-unit — output matches input units.
Symmetrical components (Fortescue's theorem, 1918) decompose any unbalanced three-phase system into three balanced sets: positive-sequence (normal ABC rotation), negative-sequence (reverse CBA rotation), and zero-sequence (in-phase on all three phases, flows through neutral/ground).
This simplifies fault analysis: each sequence network can be solved independently using the network's impedance for that sequence, then superimposed. This is the method used in IEEE Std 141 (Red Book) short-circuit studies and ANSI/IEEE Std C37 protective relay coordination.
Worked example (single line-to-ground fault, Va = 0): With Vb = 120∠-120° and Vc = 120∠120° intact, V0 = V1 = V2 = 40∠0°. Equal positive, negative, and zero sequence voltages is the signature of an SLG fault — confirmed by the calculator's "Single L-G fault" preset above.