SYMMETRICAL COMPONENETS OF POWER SYSTEMlibvolume3.xyz/electrical/btech/semester6/powersystemanalysisandstability/... · The normal operating conditions of an electric power system

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SYMMETRICAL COMPONENETS SYMMETRICAL COMPONENETS

OF POWER SYSTEMOF POWER SYSTEM

22

OUTLINE OF THE PRESENTATIONOUTLINE OF THE PRESENTATION

�� INTRODUCTIONINTRODUCTION

�� NEED FOR THE SYMMETRICAL NEED FOR THE SYMMETRICAL

COMPONENET METHODCOMPONENET METHOD

�� TECHINQUES USED TO ANALYSIS TECHINQUES USED TO ANALYSIS

SYMMETRICAL SYMMETRICAL

�� SYMMETRICAL METHODS USED TO STUDY SYMMETRICAL METHODS USED TO STUDY

POWER SYSTEM FAULTSPOWER SYSTEM FAULTS

�� CONCLUSIONCONCLUSION

�� REFERENCESREFERENCES

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INTRODUCTIONINTRODUCTION

�� The normal operating conditions of an electric power The normal operating conditions of an electric power system are occasionally disrupted because of faults.system are occasionally disrupted because of faults.

�� Analysis of power systems usually implies the Analysis of power systems usually implies the computation of network voltages and currents under a computation of network voltages and currents under a given set of conditions.given set of conditions.

�� Under many circumstances we tend to ignore the Under many circumstances we tend to ignore the unbalanced operation in the system and unbalanced unbalanced operation in the system and unbalanced operation is always present.operation is always present.

��

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An organization of power system analysis problemAn organization of power system analysis problem

��

�� Source (Reference #Source (Reference #11))

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Effects of faults on power systemEffects of faults on power system

�� Flow of excessive currentFlow of excessive current

�� Abnormal voltagesAbnormal voltages

�� Voltage elevation of system neutralVoltage elevation of system neutral

�� Induce over voltages on Induce over voltages on neighbouring equipments .neighbouring equipments .

�� Hazards to human, equipment and Hazards to human, equipment and

animals.animals.

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Need for fault analysisNeed for fault analysis

�� Design of protection system requires Design of protection system requires the knowledge of fault current.the knowledge of fault current.

�� The information obtained from the The information obtained from the

fault studies are used:fault studies are used:

�� to select the sizes of circuit breaker,to select the sizes of circuit breaker,

�� fuse and characteristic,fuse and characteristic,

�� setting of relay.setting of relay.

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Normal types of fault are:Normal types of fault are:

�� Fault due to lightningFault due to lightning

�� Tree limbs falling on the lineTree limbs falling on the line

�� Wind damageWind damage

�� Insulation deteriorationInsulation deterioration

�� VandalismVandalism

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Types of faultTypes of fault

�� Symmetrical fault :Symmetrical fault :

�� Usually three phase to ground faultUsually three phase to ground fault

�� Unsymmetrical faultUnsymmetrical fault

�� The fault is unbalanced in natureThe fault is unbalanced in nature

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Sources of Asymmetrical fault are: Sources of Asymmetrical fault are:

(Reference#(Reference#22))

1010

Sources of Asymmetrical fault are (cont.)Sources of Asymmetrical fault are (cont.)

�� One phase open circuitOne phase open circuit

�� Unbalanced in load mainly the arc Unbalanced in load mainly the arc loadsloads

1111


�� One phase open circuitOne phase open circuit

1212


�� SLG faultSLG fault

1313

Need for the symmetrical component Need for the symmetrical component

analysisanalysis

�� Negative sequence relay in generator has Negative sequence relay in generator has helped in protecting the generator from helped in protecting the generator from over heating in the event of unbalanced over heating in the event of unbalanced loads.loads.

�� The positive sequence segregating The positive sequence segregating network is used to supply the sensing network is used to supply the sensing voltage to generator voltage regulatorsvoltage to generator voltage regulators

�� Certain connections of CT and PT develop Certain connections of CT and PT develop zero sequence components that are used zero sequence components that are used in protective ground relaying scheme.in protective ground relaying scheme.

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Method of adopted for symmetrical Method of adopted for symmetrical

component analysis (cont)component analysis (cont)Mathematically:Mathematically:

�� VVaa= V= Vaa11+ + VVaa22+ + VVaa33++-------------------- VVanan

�� VVbb= V= Vbb11+ + VVbb22+ + VVbb33++--------------------VVbnbn�� ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

�� VVnn= V= Vnn11+ + VVnn22+ + VVnn33++-------------------- VVnnnn�� Where:Where:

�� VVa, a, VVb……. b……. VVn are unbalanced set of phosorsn are unbalanced set of phosors

�� VVaa11, , VVbb11…… …… VVnn1 1 first set of n balanced phasors with an angle first set of n balanced phasors with an angle 22pi/n pi/n �� between components a,b,…..nbetween components a,b,…..n

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Method of adopted for symmetrical Method of adopted for symmetrical

component analysis (cont)component analysis (cont)

Mathematically:Mathematically:

�� VVaa22, , VVbb22…… …… VVnn2 2 second set of n balanced phasors with an angle second set of n balanced phasors with an angle

44pi/n between components a, b………,…..npi/n between components a, b………,…..n

�� ……………………………………………………….……………………………………………………….

�� VVa(na(n--11), ), VVb(nb(n--11)…… )…… VVn(nn(n--11)are (n)are (n--11)th set of n balanced phasors )th set of n balanced phasors

with an angle with an angle 22pi(npi(n--11)/n between components a, b………,…..n)/n between components a, b………,…..n

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Phasor a or aPhasor a or a--operatoroperator

�� The phasor notation of aThe phasor notation of a--operatoroperator

1717


1818


1919

Equation in matrix formEquation in matrix form

2020

Symmetrical components for three Phase systemSymmetrical components for three Phase system

�� The nThe n--phase system presented above is of phase system presented above is of academic interest only and only the academic interest only and only the practical three phase system will be practical three phase system will be emphasised.emphasised.

�� Power is generated, transmitted and Power is generated, transmitted and consumed mostly in three phase only.consumed mostly in three phase only.

��

2121

Symmetrical components for three Phase system Symmetrical components for three Phase system

(cont)(cont)

�� The phasor representation of three The phasor representation of three phase system (source reference#phase system (source reference#22))

��

2222


(cont)(cont)

�� The positive sequence set consisting of three components The positive sequence set consisting of three components of equal magnitude, displaced by of equal magnitude, displaced by 120 120 & & 240240oo respectively respectively and having the phase sequence of abca.and having the phase sequence of abca.

�� The negative sequence set consisting of three components The negative sequence set consisting of three components of equal magnitude displaced by of equal magnitude displaced by 240 240 & & 120120o o respectively, respectively, having phase sequence of acba.having phase sequence of acba.

�� The zero sequence set of the component of which being The zero sequence set of the component of which being equal both in magnitude and and phase.equal both in magnitude and and phase.

��

��

2323


(cont)(cont)

Relations of voltage components in Relations of voltage components in matrix formmatrix form

��

2424

Symmetrical components of generatorSymmetrical components of generator

��

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Symmetrical components of generatorSymmetrical components of generator

��

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Symmetrical components of transformer (zero)Symmetrical components of transformer (zero)

��

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Fault analysis using symmetrical components Fault analysis using symmetrical components

The most common type of fault is the The most common type of fault is the single line to ground fault:single line to ground fault:

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(cont) (cont)

The sequence component connection The sequence component connection for the single line to ground fault:for the single line to ground fault:

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(cont) (cont)

�� The sequence component connection for The sequence component connection for the single line to ground fault:the single line to ground fault:

�� The sequence components are connected The sequence components are connected in series.in series.

�� The three currents in the case of SLG fault The three currents in the case of SLG fault are equal.are equal.

��

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(cont) (cont)

�� LL fault:LL fault:

3131


(cont) (cont)

�� LL fault:LL fault:

�� There is no zero sequence There is no zero sequence component due to absence of ground component due to absence of ground

return path.return path.

�� The positive and negative sequence The positive and negative sequence components are connected in components are connected in

parallel.parallel.

3232


(cont) (cont)

�� LLG fault:LLG fault:

3333


(cont) (cont)

�� LLG fault:LLG fault:

�� For the zero sequence component it For the zero sequence component it requires to add an external requires to add an external

impedance of Zimpedance of Zff++33ZZgg

�� The networks are connected in The networks are connected in parallel.parallel.

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Software available for carrying fault analysis Software available for carrying fault analysis

�� The most commonly used soft ware are:The most commonly used soft ware are:

�� MATLABMATLAB

�� EDSAEDSA

�� ETAPETAP

�� CYMECYME

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Conclusion Conclusion

�� Power system analysis using symmetrical Power system analysis using symmetrical component is very helpful in improving the component is very helpful in improving the reliability of the power system.reliability of the power system.

�� The principle adopted for the analysis of The principle adopted for the analysis of unbalanced fault system is symmetrical unbalanced fault system is symmetrical component method.component method.

�� By knowing the principle, the results By knowing the principle, the results obtained from the computer can be obtained from the computer can be analysed.analysed.

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References: References:

11. Paul M. Anderson, Analysis of Faulted Power . Paul M. Anderson, Analysis of Faulted Power Systems.Systems.

22. W.D. Stevenson, Elements of Power System . W.D. Stevenson, Elements of Power System Analysis.Analysis.

33. A.P.S Meliopoulos, Power System Grounding and . A.P.S Meliopoulos, Power System Grounding and Transients.Transients.

44. Olle. I. Elgerd, Electric Energy Systems Theory.. Olle. I. Elgerd, Electric Energy Systems Theory.

55. IEEE Transactions . IEEE Transactions

SYMMETRICAL COMPONENETS OF POWER SYSTEMlibvolume3.xyz/electrical/btech/semester6/powersystemanalysisandstability/... · The normal operating conditions of an electric power system

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