SYMMETRICAL COMPONENETS OF POWER SYSTEM

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SYMMETRICAL COMPONENETS OF POWER SYSTEM

• BY TANDIN JAMTSHO
• MScE STUDENT
• STUDENT 3226091

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OUTLINE OF THE PRESENTATION

• INTRODUCTION
• NEED FOR THE SYMMETRICAL COMPONENET METHOD
• TECHINQUES USED TO ANALYSIS SYMMETRICAL
• SYMMETRICAL METHODS USED TO STUDY POWER SYSTEM
  FAULTS
• CONCLUSION
• REFERENCES

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INTRODUCTION

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

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An organization of power system analysis problem

• Source (Reference 1)

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Effects of faults on power system

• Flow of excessive current
• Abnormal voltages
• Voltage elevation of system neutral
• Induce over voltages on neighbouring equipments .
• Hazards to human, equipment and animals.

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Need for fault analysis

• Design of protection system requires the
  knowledge of fault current.
• The information obtained from the fault studies
  are used
• to select the sizes of circuit breaker,
• fuse and characteristic,
• setting of relay.

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Normal types of fault are

• Fault due to lightning
• Tree limbs falling on the line
• Wind damage
• Insulation deterioration
• Vandalism

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Types of fault

• Symmetrical fault
• Usually three phase to ground fault
• Unsymmetrical fault
• The fault is unbalanced in nature

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Sources of Asymmetrical fault are (Reference2)
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Sources of Asymmetrical fault are (cont.)

• One phase open circuit
• Unbalanced in load mainly the arc loads

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Sources of Asymmetrical fault are (cont.)

• One phase open circuit

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Sources of Asymmetrical fault are (cont.)

• SLG fault

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

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Method of adopted for symmetrical component
analysis (cont)

• Mathematically
• Va Va1 Va2 Va3---------- Van
• Vb Vb1 Vb2 Vb3---------- Vbn
• Vn Vn1 Vn2 Vn3---------- Vnn
• Where
• Va, Vb. Vn are unbalanced set of phosors
• Va1, Vb1 Vn1 first set of n balanced phasors
  with an angle 2pi/n
• between components a,b,..n

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Method of adopted for symmetrical component
analysis (cont)

• Mathematically
• Va2, Vb2 Vn2 second set of n balanced phasors
  with an angle 4pi/n between components a,
  b,..n
• .
• Va(n-1), Vb(n-1) Vn(n-1)are (n-1)th set of n
  balanced phasors with an angle 2pi(n-1)/n between
  components a, b,..n

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Phasor a or a-operator

• The phasor notation of a-operator

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Phasor a or a-operator
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Phasor a or a-operator
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Equation in matrix form
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Symmetrical components for three Phase system

• 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.

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Symmetrical components for three Phase system
(cont)

• The phasor representation of three phase system
  (source reference2)

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Symmetrical components for three Phase system
(cont)

• The positive sequence set consisting of three
  components of equal magnitude, displaced by 120
  240o respectively and having the phase sequence
  of abca.
• The negative sequence set consisting of three
  components of equal magnitude displaced by 240
  120o respectively, having phase sequence of acba.
• The zero sequence set of the component of which
  being equal both in magnitude and and phase.

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Symmetrical components for three Phase system
(cont)

• Relations of voltage components in matrix form

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Symmetrical components of generator

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Symmetrical components of generator

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Symmetrical components of transformer (zero)

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Fault analysis using symmetrical components

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

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Fault analysis using symmetrical components
(cont)

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

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Fault analysis using symmetrical components
(cont)

• The sequence component connection for the single
  line to ground fault
• The sequence components are connected in series.
• The three currents in the case of SLG fault are
  equal.

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Fault analysis using symmetrical components
(cont)

• LL fault

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Fault analysis using symmetrical components
(cont)

• LL fault
• There is no zero sequence component due to
  absence of ground return path.
• The positive and negative sequence components are
  connected in parallel.

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Fault analysis using symmetrical components
(cont)

• LLG fault

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Fault analysis using symmetrical components
(cont)

• LLG fault
• For the zero sequence component it requires to
  add an external impedance of Zf3Zg
• The networks are connected in parallel.

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Software available for carrying fault analysis

• The most commonly used soft ware are
• MATLAB
• EDSA
• ETAP
• CYME

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

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References

• 1. Paul M. Anderson, Analysis of Faulted Power
  Systems.
• 2. W.D. Stevenson, Elements of Power System
  Analysis.
• 3. A.P.S Meliopoulos, Power System Grounding and
  Transients.
• 4. Olle. I. Elgerd, Electric Energy Systems
  Theory.
• 5. IEEE Transactions