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CONTENTS

CHAPTER 1 THE BREAKING OF A.C. CIRCUITS........................................................................................11.1 GENERAL........................................................................................................................................11.2 D.C. INTERRUPTION......................................................................................................................11.3 A.C. INTERRUPTION......................................................................................................................11.4 FAULT CURRENTS.........................................................................................................................2

1.5 RESTRIKING VOLTAGE.................................................................................................................41.6 OIL CIRCUIT-BREAKERS (OCB)....................................................................................................71.7 AIR BREAK CIRCUIT-BREAKERS (ACB).......................................................................................81.8 VACUU CIRCUIT-BREAKER (VCB)...........................................................................................1!1." OT#ER T$PES OF CIRCUIT-BREAKER......................................................................................11

CHAPTER 2 HIGH VOLTAGE SWITCHGEAR.............................................................................................122.1 GENERAL......................................................................................................................................122.2 OIL CIRCUIT-BREAKERS (OCB)..................................................................................................132.3 AIR BREAK CIRCUIT-BREAKERS (ACB).....................................................................................152.4 AIR BREAK CONTACTORS..........................................................................................................1"2.5 VACUU CIRCUIT-BREAKERS AND CONTACTORS.................................................................2!2.6 S%ITC#BOARD DISTRIBUTION........................................................................................ ......... 222.7 CIRCUIT-BREAKER CONTROL........................................................................................ ......... ..232.8 TRIP CIRCUIT SUPERVISION......................................................................................................25

2." FUSES...........................................................................................................................................262.1! CIRCUIT AND BUSBAR EART#ING DO%N................................................................................272.11 PANEL #EATERS..........................................................................................................................28

CHAPTER 3 LOW VOLTAGE SWITCHGEAR..............................................................................................293.1 GENERAL......................................................................................................................................2"3.2 CONSTRUCTION..........................................................................................................................2"3.3 LO% VOLTAGE S%ITC#BOARDS...............................................................................................353.4 FUSES...........................................................................................................................................383.5 BUSBAR BRACING & S#ORT-CIRCUIT FORCES......................................................................4!3.6 #OLLO% BUSBARS ' SKIN EFFECT........................................................................................41

CHAPTER 4 SWITCHGEAR TESTING.........................................................................................................454.1 GENERAL......................................................................................................................................454.2 ANUFACTURERS TESTS................................................................................................... ...... 45

4.3 USER C#ECKS.............................................................................................................................464.4 CURRENT INECTION TESTING.................................................................................................474.5 BUSBAR DUCTER TESTS...........................................................................................................47

CHAPTER 5 QUESTIONS AND ANSWERS.................................................................................................495.1 *UESTIONS..................................................................................................................................4"5.2 ANS%ERS.....................................................................................................................................51

REFERENCES................................................................................................................................................54

L+, R/0, + 2!!!

ELECTRICAL DISTRIBUTION E*UIPENT PART A

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CHAPTER 1

THE BREAKING OF A.C. CIRCUITS

1.1 GENERAL

T , 9 +: ,;0

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T > 9

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,-+: 9 ,;0, +@ +@ ;0 >, ,/ ,,0@ + 9+@ 0, + 3-+, @ : +: + ;@

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#;/ 0> 90,

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FIGURE 1.5RESTRIKING VOLTAGE

C:,0 0+@0,

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/@+= ;+/ ; 0

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T /: + ,0? 0 0, : =++: @+

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%: @+, 00:= 0:= +,,>@ >/, 0= 90, ,++0:= >+0:

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+/ + +>0:= 0,

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FIGURE 1.9VACUUM INTERRUPTION

@0@

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CHAPTER 2

HIGH VOLTAGE SWITCHGEAR

2.1 GENERAL

T ,

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M+0) C7##'(. T0, 0, >+0>> +? +,>>0

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T ;0+;+@

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O+0:= >, + ,@:0 >,0:= :>+0<  +@0< +: + , 9@@ 0: ++ 2.3.3. T > >, ,:=:= > ,-

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FIGURE 2.3TYPICAL HIGH VOLTAGE AIR BREAK SWITCHGEAR UNIT

HORI:ONTAL ISOLATION!

T

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2.3.2 A)# B#'+0 C)#*7)(8#'+0'# T#7*0

 A 0

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==@ +?, 0>>0+@ , +@@;0:= +? -: 9@. T0,++:=>: ?:;: +, + 0-9 >

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T ,;0 ,>0>,:+ 9> > @;

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FIGURE 2.VACUUM CONTACTOR

 A 0: = ;0 0, +0:= > 0, ,;: 0:F0= 2.7. F0= 2.7(+) ,;, 0: 0: : ,00:. T +>+ +>(=:) 0, @ : + ,,0: ,0:= +: >/0:=

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O /+ ,;0

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FIGURE 2.9TYPICAL OFFSHORE HIGH VOLTAGE SYSTEM

F0= 2." ,;, 0: 0+=+> 9> + 0

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FIGURE 2.1;TYPICAL CIRCUITBREAKER CONTROL CIRCUIT MOTOR

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I9

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FIGURE 2.11TRIP CIRCUIT SUPERVISION

I9 0 ,@ 9+0@, +? 9+0@, : ;: + 0 ,0=:+@ 0, 0:00+ : @+, + +: + -:=0, +: +: +@+> 0, 0:00+ ;: @+

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T

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E+0:=-;: : 9 ,;0+:9+

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CHAPTER 3

LOW VOLTAGE SWITCHGEAR

3.1 GENERAL

S;0

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B0:= ,>+@@ 0: ,0 + ,+@@ >: 0: +0, : +/ 0: +: LV,;0 >+0:

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F+

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9 >+:9++?, +:,0, + , 0: 0:,+@@+0:,. T 9@@;0:= ,+@@ 90 ;0 ; ,++/: 0: +

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CCB, + @+

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2-@ >@, ;0

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T @+=:0< 0, 0: 7!A ,0 + + 7 12 0>, +@ 0 :0 90 (: : 9 CB 0,@9). I:

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F0= 3.3 ,;, 0+=+>>+0 0:, + ,-, +, : >+:, +@@ 9

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 A00:+@ CC +:@, + >: : +

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>+:9+

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3.5 BUSBAR BRACING SHORTCIRCUIT FORCES

F0= 3.7 ,;, ; ,+, A +: B 0:,+@@ ,0 ,0 , : , 0:,@+,+:

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T >+=:0 9 9

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FIGURE 3.6SKIN EFFECT ELEMENT OF CONDUCTOR

T +>0: ;

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FIGURE 3.9SKIN EFFECT CURRENT IN A CONDUCTOR

 A@= F0= 3.8 ,==,, +

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0> >+ +,, +@:= 0 9@@ @:=. T 0, : : 9 @@; ,+ , @@; ,+, +/ , 9+ : : ,. T >+ ;/ 9: :, 0:,+@@+0:, 9 / @+=

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CHAPTER 4

SWITCHGEAR TESTING

4.1 GENERAL

 A@@ 0=- +: @;-/@+= ,;0>+0, @;.

4.2 MANUFACTURERS- TESTS

S;0+:0:=

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T0 +: 0>@, ,, +

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ELECTRICAL DISTRIBUTION E*UIPENT PART A 47

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• E+>0:+0: 9

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T , 0, :0@ ,@9-

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CHAPTER 5

QUESTIONS AND ANSWERS

5.1 QUESTIONS

1. %+ 0, 9:+>:+@ 099:

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18. #; 0, ,+9 :, ;: ;0+;0:= + /@+= +:,9> 9> + 0=-/@+=,;00>, , 9 / +/ +? : +

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5.2 ANSWERS

1. %0 .

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12. O0@-+?

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22. U,+@@ +0-+?

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REFERENCES

A//,)'= E,'*(#)*)(& (6 E00:)H Cotton, !"c #Macmillan$

P#)*)/,'% E,'*(#)*+, T'*,&H Cotton, !"c #%itman$

A,('#+() C7##'( E,'*(#)*+, E)''#) (1! E00:)%hilip &emp, M"c Tech, C 'n(, MI'' #Macmillan$

E,'*(#)*+, E)''#-% R''#'*' B0 (13 E00:)M ) "ay #Butterworth$

E,'*(#)* P'# S&%('$%B M *eedy, %h! #+ohn *iley$

E,'*(#)*+, T'*,& (5 E00:)' Hu(hes, !"c, %h !, C 'n(, l'' #Lon(man$

A=@+*'= E,'*(#)*+, T'*,&H Cotton, !"c #%itman$

S(+=+#= H+=80 # E,'*(#)*+, E)''#% (11 E00:)in . Beaty #Mc)raw Hill