Transcript presentation on symmetrical componenets of power system

SYMMETRICAL COMPONENETS
OF POWER SYSTEM
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OUTLINE OF THE PRESENTATION
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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
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The normal operating conditions of an electric power
system are occasionally disrupted because of faults.
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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
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Source (Reference #1)
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Effects of faults on power system
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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
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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:
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Fault due to lightning
Tree limbs falling on the line
Wind damage
Insulation deterioration
Vandalism
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Types of fault
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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:
(Reference#2)
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Sources of Asymmetrical fault are (cont.)
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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.)
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SLG fault
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Need for the symmetrical component
analysis
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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
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Vb= Vb1+ Vb2+ Vb3+---------- Vbn
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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Vn= Vn1+ Vn2+ Vn3+---------- Vnn
 Where:
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Va, Vb……. Vn are unbalanced set of phosors
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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
 ……………………………………………………….
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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
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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
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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)
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The phasor representation of three
phase system (source reference#2)
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Symmetrical components for three Phase system
(cont)
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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)
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The sequence component connection for
the single line to ground fault:
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The sequence components are connected
in series.
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The three currents in the case of SLG fault
are equal.
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Fault analysis using symmetrical components
(cont)
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LL fault:
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Fault analysis using symmetrical components
(cont)
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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)
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LLG fault:
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Fault analysis using symmetrical components
(cont)
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LLG fault:
For the zero sequence component it
requires to add an external
impedance of Zf+3Zg
The networks are connected in
parallel.
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Software available for carrying fault analysis
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The most commonly used soft ware are:
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MATLAB
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EDSA
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ETAP
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CYME
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Conclusion
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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
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