circuit breaker types and testing

7/21/2019 circuit breaker types and testing

http://slidepdf.com/reader/full/circuit-breaker-types-and-testing 1/30

A MINI PROJECT ON

CIRCUIT BREAKERS:TYPES AND TESTINGUNDER THE GUIDANCE OF

Mr.T.ANIL KUMAR

PREPARED BY :- ANUJ GUPTA

M.ARUN KUMAR

K.NARESH KUMAR

SRUJITH REDDY

VIJAY SANGWAN



INTRODUCTION

• CIRCUIT BREAKER :- A circuit breaker is anautomatically operated electrical switch desined toprotect an electrical circuit !rom damae caused byo"erload or short circuit# Its basic !unction is to detect

a !ault condition and interrupt current $ow# A!ter itoperates% a circuit breaker can be reset to resumenormal operation#

• &EE' () CIRCUIT BREAKER :- The circuit breakers are

re*uired !or the protection o! the appliances on theload side and to keep the system healthy# +ince% i! the!ault current% which has "ery hih "alue% is deli"eredto the load side then it will blow o, e"erythin#



MAIN PARTS OF A CIRCUIT BREAKER

• The main parts o! a circuit breaker are:-

)ied and mo"in contact:- these are the two main contacts o! acircuit breaker which are responsible !or makin and breakin theconnection#

+prin:- it is used to arrest the speed o! the mo"in contact whileclosin#

Bimetal strip:- a bimetallic strip is used to con"ert an temperatureinto a mechanical displacement# In a circuit breaker o! low ranes%this strip bends when heat due to hih current passes throuh it#

Electromanet:- this is used to attract the mo"in contact when a!ault occurs and the hih current passes throuh it hence%enerisin it#



OPERATION OF CIRCUIT BREAKERS

• I! somethin oes wron with the appliance and a larecurrent $ows% the electromanet will pull hard enouhto separate the contacts and break the circuit#

The sprin then keeps the contacts apart#

• A!ter the !ault is repaired% the contacts can be pushedback toether#

•

.enerally% all circuit breakers willha"e common type o! operation# There is one mo"in contact and one/ed contact# 0hen li"e wire carriesthe usual operatin current%

electromanet is not stron enouhto separate the contacts#



WHAT IS AN ARC AND ARCINTERRUPTION?

•

'urin openin o! current carryin contacts in a circuitbreaker the medium in between openin contacts becomehihly ioni1ed throuh which the interruptin current etslow resisti"e path and continues to $ow throuh this pathe"en the contacts are physically separated# 'urin the

$owin o! current !rom one contact to other the pathbecomes so heated that it lows# This is called arc#

• 0hen arc appears across the contacts o! a circuit breaker%then to etinuish it air or +)2 or "acuum or oil is usedbecause they ha"e hih dielectric strenth and will takeless time to do so# Based on these mediums they areclassi/ed into di,erent types are desined accordinly !ordi,erent "oltae le"els#



METHODS OF ARC EXTINCTION

• There are two methods o! Arc Etinction:-

3i4 5ih Resistance methods3ii4 6ow resistance method

• Hi! R"#i#$%&'" M"$!():- in this method% the resistance isincreased to such a "alue that current is decreased to a "ery low

"alue% which is done by:- Increasin the lenth o! the arc:- we know that% R7 8l9A % so i! the

lenth o! the arc is increased then the resistance will also increase#

By Reducin the area o! cross- section:- i! the area o! cross section isreduced the resistance increases3R7 8l9A4#

Coolin the arc:- coolin aent is pro"ided between the contactswhich reduces the temperature the arc#

+plittin the arc :- the arc is made to split into di,erent sections%resistance is increased due to e,ect o! coolin and lenthenin o! arc#



• L(* R"#i#$%&'" M"$!():- in A#C# when currentbecomes 1ero twice in a cycle% the arc etinctionbecomes easy# Usin the property o! A#C#% the arc can beetinuished when current becomes 1ero# )or such acase% the dielectric strenth o! the medium should be

ood or it must be impro"ed# It is possible either bycoolin or sweepin out the ionised particles#

• oreo"er% i! the dielectric strenth o! the mediumincreases rapidly then the potential di,erence betweenthe contacts can be interrupted and arc can be

etinuished#



TYPES OF CIRCUIT BREAKERS

• 'ependin upon the arc etinuishin medium CBsare classi/ed into the !ollowin types:-

3i4 (il Circuit Breaker

3ii4 Air Blast Circuit Breaker

3iii4 ;acuum Circuit Breaker

3i"4 +)2 Circuit Breaker



MINIMUM OIL CIRCUIT BREAKER

• In this type o! circuit breaker% both the contacts are

immersed in the oil% which is the dielectric medium o! thecircuit breaker#

• The oil in the circuit breaker pro"ides coolin and acts as aood dielectric and hence *uenches the arc#

• It can be used !or <<K;-=2>K;#



ADVANTAGES:-

3i4 It is a"ailable !or hih "oltae ranes#

3ii4 Arc enery is absorbed in decomposin o! oil#

3iii4 The as !ormed which is mainly hydroen% has hih di,usion

rate and hih heat absorption and thus pro"ides ood coolinproperties#

3i"4 The oil has hih dielectric strenth and pro"ides insulationbetween the contacts a!ter the arc has been /nally

etinuished and there has been time !or the oil to $ow into theap between contacts#



DISADVANTAGES:-

3i4 (il may be $ammable and can cause /re ha1ards% i! ade!ecti"e oil circuit breaker should !ail under pressureand cause an eplosion#

3ii4There is a risk o! !ormation o! eplosi"e miture with theair#

3iii4'ue to the decomposition o! the oil in the arc% the oil

becomes polluted by carbon particles% which reduces itsdielectric strenth# 5ence periodical maintenance andreplacements are re*uired#

3i"4 Reular maintenance and chanin the oil is costly#



AIR BLAST CIRCUIT BREAKER• An ACB makes use o! atmospheric air !or etinction o! arc

and hence known as Air Blast Circuit Breaker#

• The o! air blast circuit breaker is used !or the system"oltae o! ?@> K;% @? K; and e"en more% especiallywhere !aster breaker operation was re*uired#



T+,"# ( Air B%#$ Cir'/i$ Br"%0"r

• There are two types o! Air Blast Circuit Breaker:-

3a4 Aial blast circuit breaker

3b4 Cross blast circuit breaker

• A1i% B%#$ Cir'/i$ Br"%0"r:- 0hen a !ault occurs atrippin impulse is produced which causes openin o!the air "al"e# +ince the air "al"e connects theair reser"oir and the arcin chamber% a hih pressure airenters to the arcin chamber#



• This air pushes away the mo"in contact aainst thesprin pressure# The mo"in contact is separated and anarc is struck#

• At the same time hih pressure air blast $ows alon thearc and takes away the ionised ases alon with it#Conse*uently the arc is etinuished and current $ow is

interrupted#• Cr(## B%#$ Cir'/i$ Br"%0"r:- In this type o! breaker%

an air-blast is directed at riht anles to the arc# Thecross blast lenthens and !orces the arc which helps inbetter etinction o! the arc#



•

In cross blast circuit breaker% coolinprocess is !aster than aial blast#+ince% deionisation o! air much !asterin this case and hence the arcetinction#

• Also% arc due to small currents ise,ecti"ely eliminated which is no thatood in aial blast#



ADVANTAGES:-

Air blast circuit breaker has some speci/c ad"antaeso"er oil circuit breaker which are listed as !ollows%

3i4 There is no chance o! /re ha1ard caused by oil#

3ii4 The breakin speed o! circuit breaker is "ery hih#

3iii4 Arc *uenchin is much !aster#

3i"4 As the duration o! arc is smaller% so lesser amount o!heat is produced !rom arc to current carryin contacts

hence the ser"ice li!e o! the contacts becomes loner#

3"4 Re*uires much less maintenance compared to oil circuitbreaker#



DISADVANTAGES :-

3i4 In order to ha"e !re*uent operations% it is necessaryto ha"e suciently hih capacity air compressor#

3ii4)re*uent maintenance o! compressor% associated airpipes and automatic control e*uipments is alsore*uired#

3iii4'ue to hih speed current interruption there isalways a chance o! hih rate o! rise o! re-strikin"oltae and current choppin#

3i"4There also a chance o! air pressure leakae !rom airpipes Dunctions#



VACUUM CIRCUIT BREAKER

• A V%'//2 Cir'/i$ Br"%0"r is such kind o! circuit

breaker where the arc *uenchin takes place in "acuum# The technoloy is suitable !or mainly medium "oltae

application# The "acuum pressure inside a "acuuminterrupter is normally maintained at < E 2 bar#

• The "oltae rane !or which ;CB is commonly usedis !rom =#2 K; to F2K; but it can be used upto<@>K;#



ADVANTAGES :-

3i4+er"ice li!e o! "acuum circuit breaker is much loner

than other types o! circuit breakers#

3ii4 It has compact si1e hence weihs less and is suitable tobe used anywhere#

3iii4There is no chance o! /re ha1ard as oil circuit breaker#

3i"4It is much en"ironment !riendly3pollution !ree4 than +)2

Circuit breaker#

3"4Replacement o! "acuum interrupter is much con"enient#

3"i4 It is suitable !or repeated operatin duty#



Di#%)3%&$%"#:-

3i46oss o! "acuum due to transit damae or !ailure makes

the entire interruption useless and it cannot be repairedat site#

3ii4It needs additional sure suppressors in parallel with

each phase !or interruption o! low maneti1in currentsin certain rane#

3iii4;acuum circuit breakers are uneconomical abo"e F2k;and +)2 breakers ha"in e*ui"alent properties iseconomical# 5ence !or E5; 3"oltaes abo"e ?Fk; 4systems +)2 circuit breakers are employed#

3i"4It is uneconomical to manu!acture "acuum interrupters

in small *uantities#



SULPHUR HEXAFLOURIDE CIRCUIT BREAKER

• A circuit breaker in which the current carryin contacts operate in

sulphur hea$uoride or +)2 as is known as an +)2 circuit breaker#• The +)2 circuit breaker is used !or "oltae rane upto =2>K;#

• The +)2 is used in circuit breakers because o! the !ollowinproperties:-

4%5 It is hihly electroneati"e and hence absorbs !ree electronswhich are produced due to arcin between the contacts o! circuitbreakers#

465 It is colorless % odorless %non-toic as and non-$ammable as#

4'5 It is thermally and chemically stable#

4)5 It has hih dielectric strenth3 almost ?#F> times that o! air4# 4"5 It has the property o! !ast recombination a!ter arc is

etinuished which makes it < times moree,ecti"e in arc *uenchin compared to air#



• The below diarams shows how a +)2 circuit breakerworks:-



A)3%&$%"#:-

The +)2 circuit breaker has the !ollowin ad"antaes:-

3i4 Ecellent arc *uenchin property#

3ii4 Its per!ormance is not a,ected with the "ariations inthe atmospheric conditions#

3iii4 It i"es noiseless operation and doesnGt make sound

like air blast circuit breaker#3i"4 It re*uires minimum maintenance say% once in !our to

ten years dependin upon numbers o! times itoperated#

3"4 There is no reduction in the dielectric strenth propertyo! +)2 as since there are no carbon particles !ormeddurin the arcin#

3"i4 It is suitable !or "ery hih "oltae rane#

3"ii4The physical and chemical properties o! +)2 as is real

ad"antae o! +)2 CB#



Di#%)3%&$%"#:-

The disad"antaes o! the +)2 circuit breakers are as !ollows:-

3i4 Imper!ect Doints leadin to leakae o! the +)2 as#Continuous monitorin de"ices are re*uired#

3ii4 +)2 as is su,ocatin to some etent# In case o! leakae inthe breaker tank +)2 as bein hea"ier than the air settlesin the surroundins and may lead to su,ocation o! the

operatin personnel# 5owe"er it is not poisonous#

3iii4 Arced +)2 as is poisonous and should not be inhaled#

3i"4+)2 as hih cost and hence makes the circuit breaker a bitcostly#

3"4 +)2 is a reen house as and sa!ety reulations must bekept under consideration !or its usae#

BREAKING CAPACITY OF A CIRCUIT



BREAKING CAPACITY OF A CIRCUITBREAKER

• Br"%0i& '%,%'i$+ or i&$"rr/,$i& '%,%'i$+ is the currentthat a circuit breaker is able to interrupt without bein

destroyed#

• Breakin capacity is epressed in ;A by takin into account therated breakin current and rated ser"ice "oltae# Thus i! HI isthe rated breakin current in amperes and H; is rated ser"iceline "oltae in "olts% then !or a three phase circuit

Breakin Capacity J F L ; L I L < 2 ;A

• Breakin Capacity o! +)2 circuit breaker 3 at the sub station4%

J FL<F?L@

J M<@@#M2 ;A

• Breakin Capacity o! ;acuum circuit breaker3 at the sub station4%

J FLFFL?>

J <@?N#M ;A



BREAKER

• akin capacity o! a circuit breaker is the maimum current whichthe breaker can conduct at the instant o! closin# The makin

capacity is considered to the peak "alue o! the /rst cycle o! subtransient current#

• akin capacity is epressed in ;A by takin into account the ratedcurrent and rated ser"ice "oltae# Thus i! HI is the rated current in

amperes and H; is rated ser"ice line "oltae in "olts% then !or athree phase circuit

M%0i& '%,%'i$+7 8.9 Br"%0i& C%,%'i$+

7 ;.<< V I => @ MVA

• akin Capacity o! +)2 circuit breaker 3 at the sub station4%

J ?#>LBreakin capacity J?#>L FL<F?L@ J ??N2?#@ ;A

• akin Capacity o! ;acuum circuit breaker3 at the sub station4%

J ?#>LBreakin capacity J ?#>L FLFFL?>

JF>=?#> ;A



GENERAL TESTS ON CIRCUITBREAKER

• The !ollowin tests are conducted on a circuitbreaker:-

3i4 +ustained low !re*uency tests

3ii4 5ih ;oltae '# C# Test

3iii4 +ure Test or Impulse Test

S/#$%i&") (* r"/"&'+ $"#$:- this test is usuallyconducted on power !re*uency i#e# >51 in India% on

an insulatin specimen to determine and ensure thedielectric strenth and dielectric losses o! the

material#



• Hi! 3($%" D.C. $"#$:- 5ih "oltae 'C test isnormally applicable to the those e*uipments which are

used in hih "oltae 'C transmission system# But this testis also applicable !or hih "oltae AC e*uipments% whenhih "oltae AC testin is not possible due to una"oidablecondition# )or eample mainly at site% a!ter installation o!e*uipments it is *uite dicult to arrane !or

hih "oltae alternatin power so 'C is employed#

• In hih "oltae direct current test o! AC e*uipment%direct "oltae about two times o! the normalrated "oltae is applied across the e*uipment under test!or <> minutes to <#> hours and thatGs how this test isdone#



• S/r" $"#$:- +ure test or impulse tests are "ery hihor etra hih "oltae tests% carried out to /nd out the

in$uences o! sures or lihtnin on the transmissione*uipment# &ormally direct lihtenin strokes ontransmission line is "ery rare but it must be ready towithstand with such conditions#

•

The "oltae may e"en rise to hih "alues in the e"en o!a !ault and it must not et damaed due to o"er"oltae disturbances#

• The wa"e !orm shows the "ariation o! "oltae with time

when test is carried out#



THANK YOU

Documents

circuit breaker types and testing