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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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Contd.

(

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Contd.

)

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Contd.

*

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1+

So the $%ation as,

 On substituting for A-1  in eqn 3, we get

 

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Contd.

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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Contd.

22

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Contd.

23

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Contd.

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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31

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32

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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

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 Positive se$%ence reactance diagram

42

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 /egative se$%ence reactance diagram

43

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5ero se$%ence reactance diagram

44

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 "han0 6o%