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LT SWITCHGEAR 15.1
CHAPTER-15
LT SWITCHGEAR
SNO.1. BUS BAR ARRANGEMENT2. CHANGE OVER SCHEME3. CONTROL AND
AUX. SUPPLY BUS LAYOUT4. PROTECTIVE RELAYS AT INCOMERS AND
BUSCOUPLERS5. EARTHING OF SWITCHGEARS6. SWITCHING OF LOADS7. AIR
CIRCUIT BREA ERS!. PROTECTIVE THERMAL RELAYS AND FUSES
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TOPIC LT SWITCH GEAR BUS BARS ARRANGEMENT.
A typical !" a# a##a$%&'&$t () LT "*itc+ i" "+(*$ i$
)i%,1-. T+& a#& 2 "(!#c&" ()/0 p(* "!pply ($& $(.
)#(' t#a$")(#' 1 3 (t+ )#(' t#a$")(#' 2. T+& /0"!pply t'i$al"
() t#a$")(#'" a#& c($$&ct&0 t( i$c('i$% t'i$al"
i$0i4i0!al #&a "i.& T# 1 t( 61 a$0 T# 2 t( 6/ t+#(!%+
Al!'i$!'7c(pp "t#ip" / 8 c(#& ca l&". I)al!'i$!' (# c(pp
"t#ip" a#& !"&0 t+a$ t+&"& "t#ip" +(!"&0 i$ a
0!ct. Call&0 !" 0!ct t+&(!t %(i$% t'i$al" () t+&
#&a " a#& c($$&ct&0 t( t+& +(#i9($tal !" a#" ()
t+&i#i$0i4i0!al "&cti($. Call&0 "&cti($ A 3 B. By
"*itc+i$% O$ t+& #&a 61 3 6/ t+&
p(* "!pply ca$ & )&0 t( "&cti($,A a$0 B
#&"p&cti4&ly. T+& !"" a# :H(#i9($tal;
()"&cti($,A3B &ER SCHEME.
C+a$%& (4 '&a$" t( )&&0 (t+ t+& "&cti($
A 3 B )#(' ($& "(!#c& i) t+&"&
"&cti($"&a#li )&0 )#(' i$0i4i0!al "(!#c& (# t(
)&&0 t+& i$0i4i0!al "&cti($ )#(' (*$ "(!#c&
i)&a#li (t+ t+& "&cti($ )&0 )#(' ($&
"(!#c&.
T+& a#& 2 typ&" () c+a$%& (4
"c+&'&".
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LT SWITCHGEAR 15./
1. Li4& !" c+a$%& (4 2. ?&a0 !" c+a$%& (4
1. Li4& !" c+a$%& O4 Sc+&'&= T+i" c+a$%& (4
"c+&'& i" ($ly applica l& *+&$
"(!#c& 132 a#& "y$c+#($i9&0. @(# t+i" c+a$%& (4
'&t+(0" i" %i4&$ &l(*=
E
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LT SWITCHGEAR 15.-
5. B,:I7L; 0&)&ct #&lay;. It i" &$%i9&0 y
"y$c+#($i9&0. C+&c #&lay it 0&)&ct" t+& I7L
t(cl("& t+& #&a i$ ca"& () li4& c+a$%& (4
c($0iti($ )(# I7C" #&a cl("i$%.
i; I$ c('i$% 4(lta%& "+(!l0 & . D () "y"t&'
4(lta%& it i" '(!$t&0 y U7> 1 #&lay.ii; A$y i$c('
#&a a$0 !" c(!pl :62; *a" $(t t#ipp&0 )a!lt.
iii; B#&a i" i$ "ic& p("iti($.
CLOSING CIRCUIT O@ BUS COUPLER :62;
E, (# U7>,- a" t+& ca"& 'ay &
E,1 a$0 U7F-. T+&lay U7>,1 *ill %i4& t+& t#ippi$%
c(''a$0 t( I$c(' 1. T+& a!t( cl("i$% ci#c!it *illc+&c I$c('
1 i" O)) &".
B!",A N( )a!lt &"B!",B >(lta%& D , &"B!",A
>(lta%& / D , &"
I) all t+& c($0iti($ )!l)ill&0 t+& !" c(!pl *ill
cl("& a$ a!t( '(0&.
T+& t#ippi$% ci#c!it al'("t "a'& )(# i$c('" a$0 !" c(!pl
&,1 3 U7>,2 i$ca"& () !$0 4(lta%& )(# I7C,1 3
I7C,2a$0 !p,"t#&a' t#ip.
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LT SWITCHGEAR 15.5
T+& #&a *ill t#ip i$ )(ll(*i$% c($0iti($
1. By 'a$!al "p#i$% #&t!#$ "*itc+2. @a!lt i$ a$y !"
/. Up,"t#&a' () i$c('" &c('& ())-. I$c('
&ca'& !$0 4(lta%& 0!& t( (t+ #&a"($".
:SNO,111;
TOPIC= CONTROL AN? AU .SUPPL BUS LA OUT.
I$ PCC7MCC t+& #&a " a$0 &l&ct#('a%$&tic
c($t#act(# typ& )&&0" !"&0 t( )&0
t+& p(* "!pply t( t+& !" a#" '(t(#" (# t( (t+ & ?C
!" a# )(# tappi$% t+& t#ippi$% "!pply () t+& #&a ".2.
MO?C !" a# )(# tappi$% t+& cl("i$% a$0 "p#i$% c+a#%i$% '(t(#
"!pply./. MO> AC !" a# )(# tappi$% t+& c($tact(#
)&&0" c($t#(l "!pply i$ "ic& p("iti($.-. MO>AC !"
)(# "pac& +&at i$ PCC7MCC Pa$&l" a$0 t&"t c($t#(l
"!pply )(# c($tact(#
)&&0" i$ t&"t p("iti($.
SWITCHING OF LOADS
S*itc+i$% &J!ip'&$t '!"t cl&a#ly & "!ita l&
)(# "*itc+i$% $(#'al a$0 *+&$ #&J!i#&0 a $(#'al
c($0iti($"() t+& ci#c!it i$ *+ic+ it i" "it!at&0. All
ci#c!it" c($"i"t () "i&"7pa#all&l a##a$%&'&$t" ()
#&"i"ta$c&acta$c& a$0 capacita$c& a$0 0!#i$%
"*itc+i$% t+&"& c('p($&$t" *ill p#(0!c&
#&"($a$c&" () 0i))&$t)(#'". T+& "*itc+i$%
&J!ip'&$t '!"t t+&)(#& & capa l& ()
"a)&ty *it+"ta$0i$% t+&"& #&"($a$t
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c($0iti($" 0!#i$% t+& "*itc+i$% (pati($. T+& "*itc+i$%
c($0iti($" 0&"c#i &0 &l(* a#&
#&%!la#ly&$c(!$t&0.
NORMAL SWITCHING CON?ITIONS
1. S+!$t Capacit(# Ba$ "*itc+i$%= W+&$ "*itc+i$% a "+!$t
capacit(# a$ t+& l(a0 i" p!#&ly
capaciti4&. T+& "(!#c& "i0& () t+& ci#c!it
#&a *ill i$cl!0& !" a# capacita$c& t( &a#t+ t+i"
&i$% "'all c('pa#&0 *it+ t+& l(a0 capacita$c& a$0
"i&" #&acta$c&. T+& &$%y "t(#&0 i$
t+&l(a0 capacit(# i" 0i"c+a#%&0 t( t+& !" a# "+!$t
capacita$c& a$0 "i&" i$0!cta$c& t( ca!"& a
+i%+)#&J!&$cy ("cillati($. La#%& c!##&$t" *ill )l(*
ac#("" t+& (p&$i$% c($tact %ap a$0 0a'a%& t(
a#&c($t#(l 0&4ic&" 'ay (cc!#.
2. O4+&a0 Li$& a$0 Ca l& S*itc+i$%= B(t+ (4+&a0
li$& a$0 ca l& "*itc+i$% c($0iti($" p#&"&$t p#(
l&'" "i'ila# t( t+("& () capacit(# "*itc+i$%.
I$ t+& ca"& () (4 +&a0 li$& t+& *ill &
0i"t#i !t&0 capacita$c& &t*&&$ t+&
p+a"&" a$0 t( &a#t+al($% t+& li$& i$t"p"&0 *it+
0i"t#i !t&0 li$& i$0!cta$c&. T+& l(a0 c!##&$t
i" a%ai$ "'all a$0it" i$t#!pti($ i" p#( a l& at t+& )i#"t
a4aila l& c!##&$t 9(. T+i" *ill l&a4& a c+a#%&
($ t+& li$&*+ic+ 'ay #&"!lt i$ a t#a4&lli$%
*a4& p#(pa%ati$% al($% t+& li$& t( t+& )a# &$0
*+& it *ill #&)l&cta$0 #&t!#$ t( t+& ci#c!it
#&a .
A )!#t+ p#( l&' 'ay (cc!# *+&$ "*itc+ a$ (4 +&a0
li$& *+ic+ i" t'i$at&0 at a$ !$l(a0&0t#a$")(#'. T+&
c(' i$ati($ () li$& capacita$c& a$0 'ay &
%&$at&0.
-. S+!$t R&act(# S*itc+i$% S+!$t #&act(#" a#&
()t&$ !"&0 t( c('p&$"at& )(# t+&
capacita$c& ()+i%+ly l(a0&0 li$&". T+&y 'ay &
)#&J!&$tly "*itc+&0 0&p&$0i$% ($ t+&
li$& l(a0i$% #&%i'&".S+!$t #&act(# "*itc+i$%
p#&"&$t" (4!"& "*itc+i$% c($0iti($" )(# a ci#c!it
#&a a$0 )#&J!&$t'ai$t&$a$c& 'ay &
$&c&""a#y.
5. Si&" R&act(# S*itc+i$%= Si&" #&act(#" a#&
"a'& ti'&" !"&0 t( li'it t+& "+(#t ci#c!it
)a!ltcapacity &t*&&$ t+& t*( c($$&ct&0
"&cti($" () a "!pply "y"t&' "+(!l0 a )a!lt (cc!# ($ t+&
ci#c!it"i0& () t+& #&act(# t+i" *(!l0 ca!"& a
#&lati4&ly +i%+ )#&J!&$cy t#a$"i&$t ($ t+&
#&act(# "i0& () t+&ci#c!it #&a a$0 a l(*
)#&J!&$cy ("cillati($ ($ t+& !" a# "i0&. T+!"
ci#c!it #&a " )(# "i&"#&act(# "*itc+i$% 0!ti&"
$&&0 t( & t&"t&0 )(# t+&"& "p&ci)ic
c($0iti($".
. ?i"c($$&ct(# S*itc+i$%= W+il"t 0i"c($$&ct(#"
%&$ally +a4& ($ly t( "*itc+ t+& "'all
capaciti4&c!##&$t" a""(ciat&0 *it+ a "&cti($ () !"
a# &t*&&$ t+& 0i"c($$&ct(# a$0 ci#c!it #&a
t+i" ca$ca!"& ctai$ p#( l&'". @i#"tly t+&
0i"c($$&ct(# '!"t & capa l& () "ati")act(#ily "*itc+i$%
t+&
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LT SWITCHGEAR 15.
'a
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LT SWITCHGEAR 15.
1. @i#& #i" a$0 'ai$t&$a$c& a""(ciat&0 *it+
t+& !"& () (il a#& &li'i$at&0.
2. A#ci$% p#(0!ct" i$ ai# a#& %&$ally c('pl&t&ly
#&'(4&0 *+&a" (il 0&ti(#at&" *it+
"!cc&""i4& #&a i$% (pati($. T+&)(#& t+&
&
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LT SWITCHGEAR 15.
Acti($ t+a$ at +i%+ c!##&$t" !t t+& '(4&'&$t ()
t+& a#c i$t( t+& c+!t& t&$0" t( &c('&
"l(*a$0 +i%+ "p&&0 i$t#!pti($ i" l&"" a""!#&0.
