Substation1
Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

symmetrical component
the method by which unbalanced three-phase power system operation (particularly unbalanced fault performance) can be efficiently analyzed. Symmetrical components convert unbalanced line currents and voltages to three sets of balanced sequence components: positive sequence, negative sequence, and zero sequence.

The transformed phasor variables fC-0s are obtained by applying the appropriate Fortescue transformation to any multi-phase set of phasor variables. Denoted, f+s;f-s;f0s, these are the positive sequence, negative sequence, and zero sequence components, respectively. The variables are so named because any unbalanced
set of currents can be expressed (in phasor form) in terms of

1. a balanced set of currents with magnitude iCs that has a phase sequence which produces counterclockwise rotor rotation in a machine (positive sequence).

2. a balanced set of phasor currents with magnitude i-s that has a phase sequence which produces clockwise rotor rotation in a machine (negative sequence), and

3. a set of three equal phasors with magnitude f0 (zero sequence) which does not produce rotor rotation in machine.