power system

1. Seminar Topic on:-
SYMMETRICAL COMPONENT OF POWER
SYSTEMS
Presented By:-
Devendra Mishra
Branch:- EN-1
Roll No:-1401421020

2. OUTLINE OF THE PRESENTATION
INTRODUCTION
NEED FOR THE SYMMETRICAL
COMPONENET METHOD
TECHINQUES USED TO ANALYSIS
SYMMETRICAL
CONCLUSION

3. INTRODUCTION
A three-phase system is said to be symmetrical when
the system viewed from any phase is similar.
Thus, in a three-phase symmetrical system the
impedances of all the three phases are equal and the
mutual impedances, if any, between the three phases are
the same.
The three phase voltages(or currents) are said to be
balanced if the magnitude of the three voltages(or
currents) are equal and they separated from each other
by 120º(electrical) in phase.
When the system is unbalance the voltages, current and
the phase impedances are in general unequal. Such a
system can be solved by a symmetrical per phase
technique known as the method of symmertical
component.

4. This method was proposed by Fortescue in 1981
and is often called the three-component method.
According to Fortescue, An unbalance set of n
phasors may be resolved in to (n-1) balanced n-
phase system of different phase sequence and one
zero-phase sequence system.
A zero-phase sequence system is one in which all
phasors are of equal magnitude and identical angle,

5. PHASE SEQUENCE
Phase-Sequence of the phasors is the order in which
they pass through a positive maximum.
 Thus, a phase sequence a b c implies that the
maxima occur in order a, b, c.
If a, b, c is taken as the positive phase sequence then
a, c, b represents the negative phase sequence.
It should be noted that for both positive & negative
phase sequence, the direction of rotation of phaser is
taken to be anticlockwise

6. The phasor representation of three phase system

7. 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 network is used to supply the
sensing voltage to generator voltage regulators
Certain connections of CT and PT develop zero
sequence components that are used in protective
ground relaying scheme

8. Method of adopted for
symmetrical component analysis
Mathematically:
Va= Va0+ Va1+ Va2
Vb= Vb0+ Vb1+ Vb2
Vc= Vc0+ Vc1+ Vc2
 Va Vb Vc are unbalance set of phasor
Va1, VbVc1 are set of positive sequence phasor
Va2, Vb2Vc2 are negative sequence phasor
Va0 Vb0 Vc0 are zero sequence phasor

10. Vp=A Vs
Then Vs=[ adjA÷|A|] Vp

11. Symmetrical components of generator

12. Symmetrical components of
transformer

13. Conclusion
Power system analysis using symmetrical
component is very helpful in improving the
reliability of the power system.
The principle adopted for the analysis of
unbalanced fault system is symmetrical component
method

14. Any query
Thank you