Unbalanced three phase system can be resolved into three balanced systems in the sinusoidal steady state, it is called Symmetrical components.
What is Symmetrical components ?
Any set of unbalanced three phase Phasors can be expressed as the sum of three symmetrical sets of balanced phasors. With this concept, unbalanced system conditions which are caused by fault types like Unbalnce Load, Earth Fault, Short Circuit can be visualized and analyzed.
What is Voltage and Current Sequence Components ?
In any three phase system, there are three sets of independent components positive, negative and zero for both Voltage and Current
Positive sequence :
Positive Sequence components, Balanced Phasors of Voltage or Current are rotating in Clockwise direction and are displaced 120 * degree apart and it will have equal magnitude of Current.
Positive Sequence components are generated because of load.
Balanced System will have Positive sequence Voltage and Current.
Negative sequence :
Negative Sequence components, Balanced Phasors of Voltage or Current are rotating in Anti Clockwise direction and are displaced 120 * degree apart.
Negative Sequence components generated because of unbalance load.
Zero sequence :
Zero Sequence components, Phasors are equal in Magnitude and are in Phase with each other. Since there is no Rotation of Phasors it is called Zero Sequence components.
- Zero Sequence current flows in Neutral or Ground.
- Zero Sequence currents generated because of earthfault/earthleakage.
- Zero Sequence is also known as DC component of the fault current.