Section I: Symmetrical Components

• Symmetrical Component Transformation
• Real and Reactive Power
• Orthogonal Transformation

Symmetrical Components

A system of three unbalanced phasors can be resolved in the following three symmetrical components:

• Positive Sequence: A balanced three-phase system with the same phase sequence as the original sequence.
• Negative sequence: A balanced three-phase system with the opposite phase sequence as the original sequence.
• Zero Sequence: Three phasors that are equal in magnitude and phase.
  

Fig. 7.1 depicts a set of three unbalanced phasors that are resolved into the three sequence components mentioned above. In this the original set of three phasors are denoted by V_a , V_b and V_c , while their positive, negative and zero sequence components are denoted by the subscripts 1, 2 and 0 respectively. This implies that the positive, negative and zero sequence components of phase-a are denoted by V_a1 , V_a2 and V_a0 respectively. Note that just like the voltage phasors given in Fig. 7.1 we can also resolve three unbalanced current phasors into three symmetrical components.

Fig. 7.1 Representation of (a) an unbalanced network, its (b) positive sequence, (c) negative sequence and (d) zero sequence.