psa

1. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021
ACHARIYA
COLLEGE OF ENGINEERING TECHNOLOGY
(Approved by AICTE and affiliated to Pondicherry University)
An ISO 9001:2008 Certified Institution
Achariyapuram, Villianur, Puducherry – 605 110.
“UNIT III-SYMMETRICAL COMPONENTS”
INSTRUCTOR
Ms.T.ABINAYA SARASWATHY M.TECH
ASSISTANT PROFESSOR
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

2. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021
 An unbalanced three-phase system can be resolved into three
balanced systems in the sinusoidal steady state. This method of
resolving an unbalanced system into three balanced phasor
system has been proposed by C. L. Fortescue. This method is
called resolving symmetrical components of the original
phasors or simply symmetrical components
 It consists of three vectors of equal magnitude, displaced from
each other by 120 degree in phase and having the same phase
sequence as the original vectors
 It consists of three vectors of equal magnitude, displaced from
each other by 120 degree in phase and having the phase
sequence opposite to that of the original vectors.
 It consists of three vectors of equal magnitude and with zero
phase displacement from each other.

3. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021
COMPUTATION OF UNBALANCED VECTORS
FROM SYMMETRICAL COMPONENTS
 In a three phase system ,three unbalanced vectors either
(Va,Vb,Vc or Ia,Ib,Ic) be the set of unbalanced voltage
vectors can be resolved into three balanced system of vectors.
 The vectors of the balanced system are called symmetrical
components. Each voltage vector can be resolved into positive,
negative and zero sequence components.
 Let Va1,Vb1,Vc1 be the positive sequence components of
Va,Vb,Vc respectively with phase sequence abc
 Let Va2,Vb2,Vc2 be the negative sequence components of
Va,Vb,Vc respectively with phase sequence acb
 Let Va0,Vb0,Vc0 be the sequence components of Va,Vb,Vc
respectively

4. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021
VECTOR DIAGRAM OF SYMMETRICAL
COMPONENTS OF UNBALANCED THREE
PHASE VOLTAGE VECTORS

5. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021
COMPUTATION OF UNBALANCED VECTORS
FROM THEIR SYMMETRICAL COMPONENTS

6. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021
COMPUTATION OF SYMMETRICAL
COMPONENTS OF BALANCED VECTORS

7. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021
COMPUTATION OF UNBALANCED VECTORS
FROM SYMMETRICAL COMPONENTS
 In a three phase system ,three unbalanced vectors either
(Ia,Ib,Ic) be the set of unbalanced current vectors can be
resolved into three balanced system of vectors.
 The vectors of the balanced system are called symmetrical
components. Each current vector can be resolved into
positive, negative and zero sequence components
 Let Ia1,Ib1,Ic1 be the positive sequence components of Ia,Ib,Ic
respectively with phase sequence abc
 Let Ia2,Ib2,Ic2 be the negative sequence components of
Ia,Ib,Ic respectively with phase sequence acb
 Let Ia0,Ib0,Ic0 be the Zero sequence components of Ia,Ib,Ic
respectively

8. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021
VECTOR DIAGRAM OF SYMMETRICAL
COMPONENTS OF UNBALANCED THREE
PHASE CURRENT VECTORS

9. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021

10. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021
SEQUENCE IMPEDANCE & SEQUENCE
NETWORKS
 The sequence impedance are the impedance offered by the
circuit elements or the power system components to the
positive ,negative , zero sequence currents
 The impedance of a circuit element when positive sequence
currents alone are flowing is called positive sequence
impedance
 Similarly , when negative sequence currents are present ,it is
called negative sequence currents are called negative sequence
impedance
 Similarly , when zero sequence currents are present ,it is called
zero sequence impedance

11. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021

12. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021

13. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021

14. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021

15. EE T61 Ms.T.Abinaya saraswathy [AP/EEE] ACET/EEE/2020-2021