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Transcript of unsymmetrical faults.ppt
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Power System Analysis
Unsymmetrical Fault
AnalysisUNIT - IV
1
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Symmetrical Components
2
The symmetrical components of three phase system are,
• Positive Sequence Components
• Neative Sequence Components
• !ero Sequence Components
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Contd.
3
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Contd.
Substitute 2 in 1
The a"ove equation can "e arrane# in matri$form as,
The a"ove equation can "e use# to compute the un"alance#voltae vectors from the %no&le#e of symmetrical
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Contd.
!
Computation of Symmetrical Components of
un"alance# vectors
"he above matri# e$%ation as,
&n prem%ltiplying above e$%ation with A'1, we get3
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(
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)
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*
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1+
So the $%ation as,
On substituting for A-1 in eqn 3, we get
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11
"he matri# e$%ation -rom above can be e#pressed as three
independentlinear e$%ations as shown below,
"he above e$%ations can be %sed to comp%te the
symmetrical componentso- the %nbalanced voltages.
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Symmetrical Components o-%nbalanced c%rrent vectors
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13
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Contd.
14
Pro"lem '
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1
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1!
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1(
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Contd.
1)
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Se$%ence mpedance and Se$%ence/etwor0
1*
Sequence impedance and networks of generator
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Contd.
2+
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Contd.
21
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22
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23
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24
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Se$%ence /etwor0 For enerator
2
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Contd.
2!
The current (o&in throuh neutral reactance is )Ia* + The ero sequence #rop from point a to roun# is ,
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Contd.
2(
ith reference to a"ove .ure, The equation for thephase-a component voltaes are,
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Contd.
2)
The ero sequence net&or% of enerator &hen theneutral is soli#ly roun#e# an# &hen the neutral isunroun#e# are sho&n "elo&+ In these case there is nochane in positive an# neative sequence net&or%
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Se$%ence impedance and networ0s o-transmission line
2*
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Se$%ence impedance and networ0s o-trans-ormer
3+
For !ero sequence , the follo&in o"servations haveto ma#e,
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33
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Se$%ence impedance and networ0s o-loads
34
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3
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3!
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3(
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Per phase e$%ivalent circ%it
3)
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3*
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Problem
4+
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Sol%tion
41
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Positive se$%ence reactance diagram
42
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/egative se$%ence reactance diagram
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5ero se$%ence reactance diagram
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"han0 6o%