The normal operating conditions of an electric
power system are occasionally disrupted because of
Analysis of power systems usually implies the
computation of network voltages and currents
under a given set of conditions.
Under many circumstances we tend to ignore the
unbalanced operation in the system and
unbalanced operation is always present.
3. Need for the symmetrical component analysis
Negative sequence relay in generator has helped in
protecting the generator from over heating in the
event of unbalanced loads.
The positive sequence segregating network is used
to supply the sensing voltage to generator voltage
Certain connections of CT and PT develop zero
sequence components that are used in protective
ground relaying scheme.
7. Symmetrical components for three Phase
The n-phase system presented above is of
academic interest only and only the practical three
phase system will be emphasised.
Power is generated, transmitted and consumed
mostly in three phase only.
9. The positive sequence set consisting of three
components of equal magnitude, displaced by 120 &
respectively and having the phase sequence of
The negative sequence set consisting of three
components of equal magnitude displaced by 240 &
respectively, having phase sequence of acba.
The zero sequence set of the component of which
being equal both in magnitude and and phase.