SYMMETRICAL COMPONENETS OF POWER SYSTEM

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SYMMETRICAL COMPONENETS SYMMETRICAL COMPONENETS OF POWER SYSTEMOF POWER SYSTEM

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OUTLINE OF THE PRESENTATIONOUTLINE OF THE PRESENTATION

INTRODUCTIONINTRODUCTION NEED FOR THE SYMMETRICAL COMPONENET NEED FOR THE SYMMETRICAL COMPONENET

METHODMETHOD 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 #1)Source (Reference #1)

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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#2)(Reference#2)

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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

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Sources of Asymmetrical fault are (cont.)Sources of Asymmetrical fault are (cont.) One phase open circuitOne phase open circuit

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

SLG faultSLG fault

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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= Va1+ a1+ VVa2+ a2+ VVa3+---------- a3+---------- VVanan

VVbb= V= Vb1+ b1+ VVb2+ b2+ VVb3+---------- b3+---------- VVbnbn ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

VVnn= V= Vn1+ n1+ VVn2+ n2+ VVn3+---------- n3+---------- VVnnnn Where:Where:

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

VVa1, a1, VVb1…… b1…… VVn1 first set of n balanced phasors with an angle 2pi/n n1 first set of n balanced phasors with an angle 2pi/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: VVa2, a2, VVb2…… b2…… VVn2 second set of n balanced phasors with an angle 4pi/n n2 second set of n balanced phasors with an angle 4pi/n

between components a, b………,…..nbetween components a, b………,…..n

………………………………………………………………………………………………………………..

VVa(n-1), a(n-1), VVb(n-1)…… b(n-1)…… VVn(n-1)are (n-1)th set of n balanced phasors with an n(n-1)are (n-1)th set of n balanced phasors with an

angle 2pi(n-1)/n between components a, b………,…..nangle 2pi(n-1)/n between components a, b………,…..n

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Phasor a or a-operatorPhasor a or a-operator

The phasor notation of a-operatorThe phasor notation of a-operator

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Equation in matrix formEquation in matrix form

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Symmetrical components for three Phase systemSymmetrical components for three Phase system

The n-phase system presented above is of The n-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.

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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#2)phase system (source reference#2)

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The positive sequence set consisting of three components The positive sequence set consisting of three components of equal magnitude, displaced by 120 & 240of equal magnitude, displaced by 120 & 240oo 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 240 & 120of equal magnitude displaced by 240 & 120o 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.

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

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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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Fault analysis using symmetrical components Fault analysis using symmetrical components (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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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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LL fault:LL fault:

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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.

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LLG fault:LLG fault:

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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+3Z+3Zgg

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:

1. Paul M. Anderson, Analysis of Faulted Power 1. Paul M. Anderson, Analysis of Faulted Power Systems.Systems.

2. W.D. Stevenson, Elements of Power System 2. W.D. Stevenson, Elements of Power System Analysis.Analysis.

3. A.P.S Meliopoulos, Power System Grounding and 3. A.P.S Meliopoulos, Power System Grounding and Transients.Transients.

4. Olle. I. Elgerd, Electric Energy Systems Theory.4. Olle. I. Elgerd, Electric Energy Systems Theory.

5. IEEE Transactions 5. IEEE Transactions

SYMMETRICAL COMPONENETS OF POWER SYSTEM

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