4. electrical switchgears.ppt

8/20/2019 4. ELECTRICAL SWITCHGEARS.ppt

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SWITCHGEARS

BY

LIl


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Switchgear is a generic term and includes the entire

switching deices and their com!ination with associatemeasuring" #rotecting and regulating e$ui#ment%

The assem!lies of such deices and e$ui#ment with associaconnections" accessories" enclosures and su##orting s

intended" in #rinci#le" for use in connection with the gtransmission" distri!ution and conersion of electric energy a switchgear%

DEFINITIONS

Switchgear


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WHY DO WE NEED SWITCHGEARS

Switchgears are necessary at eery switching #oint in the #owsystem !ecause there are seeral oltage leels and fault lewhich has to !e controlled and #rotected !y access

Switching deices and for isolation" if the need arises%

Examples ! Switchgears

(a) Circuit *rea+ers%(!) Isolators (,isconnector or ,isconnecting Switch)%(c) Earthing Switch%(d) Lightning Arrestor%(e) Current Transformer%(f) -oltage (.otential) Transformer%


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(g) .rotection Relays%(h) 0uses%(i) Contactors%

() Load Switches (Ring 2ain3nits)%(+) 0eeder .illars%(l) Reactors%

C"ti"#ati" "switchgears


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$etal%cla& switchgear

2etal enclosed switchgear in which com#onents are arranse#arate com#artments with metal enclosures intended

earthed% There will !e se#arate com#artments at least ffollowing com#onents 5 each main switching deice6 com#connected to one side of a main switching deice" e%g% feeder6and com#onents connected to the other side of the main swdeice" e%g% !us !ars

C'ASSIFICATION OFSWITCHGEARS


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$etal E"clse& Switchgear

Switchgear assem!lies with an e8ternal metal enclosure inteearthed" and com#lete e8ce#t for e8ternal connections%


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CIRC(IT BREA)ER

A mechanical switching deice" ca#a!ma+ing" carrying and !rea+ing currents

normal circuit conditions" and also mcarrying for a s#eci:ed time and !rcurrents under s#eci:ed a!normal conditions such as those of short&circuit%


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C'ASSIFICATION OF CBs


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(a* RATED +O'TAGE


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(!) 2E,I32 >0 ARC E?TI@CTI>@

(i) Air & (Atmos#heric aircom#ressed air)%(ii) ,ielectric >il (Transformer >il)%(iii) Sul#hur He8aBuoride (S09) Gas%(i) -acuum%

(ii),ielectric >il (Transformer >il) CB5 in these ty#e of circuit !rea+ers" the contacts#roide insulation !etween the lie #art and earthed metal tan+ and also #rimarilyWe hae them as 5a) *ul+ oil circuit !rea+ers(*>C*) for oltages of range 1 - to // +-% As shown


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(!) 2inimum >il Circuit *rea+ers (2>C*s)

These ty#es of circuit !rea+ers utilise oil as the interru#ting media% Howunli+e !ul+ oil circuit !rea+ers" these designs #lace the interru#ting units in

insulating cham!ers at lie #otential% This feature of the design of 2>C*s reduces the re$uirement of oil" an

these !rea+ers are therefore +nown as minimum oil circuit !rea+ers% These d

are aaila!le in oltages ranging from 1 - to ;97 +- using the multi&!rea+techni$ue

Ty#icaliew of /9+- 2>C*

Cross&section ofinterru#tingcham!er


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(ii) Air & (Atmos#heric aircom#ressed air) 5 Air Circ#it Brea,er This is the ty#e of !rea+er in which the contacts >#en and close in air at atmos#ressure% In general" its use is restricted to low oltage a##lications or high seinstallations where the ris+ of an oil :re or oil contamination of the enironmenthigh to !e tolerated%

(a) 2ain .arts of an air circuit !rea+er trolley

(!) Cooling #late arc ch


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(c) Arc chute with magnetic coil (d) Arc chute with metal arc

This circuit !rea+er #reents the resum#tion of arcing after current Dero !situation wherein the contact ga# will withstand the system recoery oltage arc oltage in e8cess of the su##ly oltage% This state can !e achiee throufollowing ways5 Intense cooling of the arc #lasma" so that the oltage gradient is ery high6 Lengthening the arc #ath to increase the arc oltage6 and

S#litting u# the arc into a num!er of series arcs%


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Air Blast Circ#it Brea,ers -ABCBs*

This ty#e of circuit !rea+er has !een used earlier for o#en terminal H- asystem

oltages of '47 +-" and 4 +- u# to ;97 +-" es#ecially where faster !reawas

re$uired% Each interru#ter consists of a #orcelain insulator" mounted on the air inlet manie8haust cham!er :8ed at the o##osite end of the #orcelain as shown in the :g

The moing contact assem!ly consists of a chromium&co##er contact cou#led tmeans of an insulated tie rod that moes inside the contact tu!e% The main currencontact is transferred to the contact tu!e !y means of transfer contact :nge

ti# is #roided at the end of the moing contact% The moing contact is maintanormally closed

#osition with the :8ed contact !y s#rings%


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(iii*SF. Gas Circ#it Brea,ers5 in this ty#e of C* the arc $uenching medium is she8aBuoride(S09) gas hence" the contacts o#en and close in the gas% These circuit are aaila!le for com#lete range of medium oltage and high oltage a##lica


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S09 C*&Interru#ter

-i/*+ac##m Circ#it Brea,ers -+CBs*


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-i/*+ac##m Circ#it Brea,ers -+CBs*

In a acuum circuit !rea+er" the arc interru#tion ta+es #lace in acuum% This technfound to !e most suita!le for medium oltage a##lication though the e8#erimenfor ;'%7 +- and 147 +- hae !een deelo#ed" they were not found to !e commerciaIt has a steel arc cham!er in the centre and symmetrically arranged ceramshown in the :g% !elow5


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The moing contacts are made moa!le !y the use of !ellows% The arc cham!er is welded to the housing Banges" w

turn" are !raDed to metallised ceramic insulators" thus ghermetically sealed interru#ter% The acuum #ressure is gene!ar%

The material of the contacts #lays a ery im#ortant oerall #erformance of the acuum circuit !rea+er%

common material or alloys in use today are5 Cu*i" CuCr" these" CuCr oers the most ideal solution for all ratings of from < +A to 9/ +A% With this material" the current cho##ing!een +e#t down to as low as ' to / am#s%


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Operati"g mecha"ism

The #rimary function of a circuit !rea+er mechanism is to #roide the meano#ening and closing the contacts%

-i* Spri"g Chargi"g

$echa"isms The energy of this mechanism is stored in closing s#rings% The stored energy is athe circuit !rea+er on command following the release of the closing latch% Commedium oltage outdoor and indoor ty#e circuit !rea+ers%

S#ring 2echanism%


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-ii* 0"e#matic $echa"ism These mechanisms o#en and closes the contact #neumatically i%e my the #ressuriDed air% #neumatic mechanisms use an air #iston to drie the closlin+age and to charge a set of o#ening s#rings% 3sually found in A*C*" oil

ty#e of C*s% This is shown in the :gure !elow5

-iii* H & li $ h i


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Hydraulic mechanisms constitute only a ariation of the #neumatic mechanienergy" in most cases" is stored in a nitrogen gas accumulator" and the incom#hydraulic Buid !ecomes a Buid o#erating lin+ that is inter#osed !etween theaccumulator and a lin+age system%

-iii* H1&ra#lic $echa"isms

The storage method of the energy can !e either the nitrogen gas accumulator os#ring assem!ly" which acts as an energy accumulator%

-&*T ! t ti


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-&*T1pe ! c"str#cti"

(e*Str#ct#ral Desig"


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(e*Str#ct#ral Desig"

In dead&tan+ circuit !rea+ers" the switching deiceis located" with suita!le insulator su##orts" insidea metallic essel(s) at ground #otential and :lledwith insulating medium% In dead&tan+ circuit

!rea+ers" the incoming and outgoing conductorsare ta+en out through suita!le insulator !ushings"and low oltage ty#e current transformers arelocated at the lower end of !oth insulator!ushings" i%e% at the line side and the load side%

In lie&tan+ circuit interru#ter(s) is located !ushing" at a #otentiala!oe ground #otential% T!rea+ers are chea#er transformer)"and re$uires#ace%


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An isolator & also called disconnector switch or sim#ly discois !asically a no&load switch design to o#erate under condition%

ISO'ATOR

Circuit !rea+er always tri# the circuit !ut o#en contacts ocannot !e isi!le #hysically from outside of the !rea+er a

why it is recommended not to touch any electrical circuswitching o the circuit !rea+er% So for !etter safety theresome arrangement so that one can see o#en conditiosection of the circuit !efore touching it%

Isolator o#ens only after the o#ening of the circuit !rea+er closes :rst !efore the C%*% Isolator is interloc+ed with circuitsuch that wrong o#eration is aoided%

Basic cmp"e"ts ! a"


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Basic cmp"e"ts ! a"Islatr

T1pical Applicati"


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T1pical Applicati"

There are dierent ty#es of isolators aaila!le de#ending u#on


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There are dierent ty#es of isolators aaila!le de#ending u#onsystem re$uirement% These are5

Si"gle Brea, +ertical Brea, Islatr


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Si"gle Brea, +ertical Brea, Islatr

Si l Si& 2 , I l t


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Si"gle Si&e 2rea, Islatr

C t B , I l t


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Ce"ter Brea, Islatr

D 2l B , I l t


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D#2le Brea, Islatr


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0ANTOGRA0H ISO'ATOR


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2a8imum oltage

,ielectric Withstand .ower 0re$uency Continuous current .ea+ Withstand current(#ea+

Assym)

Short&time Withstand current(sym) Closing time Ice *rea+ing Ca#a!ility 2echanical >#erations Load interru#ting current

Rated Characteristics@ame#late ,ata

2a+er @ame and ,esignation num Serial num!er 0re$uency 2a8imum -oltag Continuous curre Allowa!le continu

.ea+ withstand c Short&time withst

Short&time curre Lightning im#uls 2echanical >#er Load interru#ting


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Earthi"g Switch


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An Earthing switch is a deice used to discharge to earth" residual charges tra##ed on a line after its o#ening%

An Earthing switch is normally connected !etween the conductor and earth% (Fust !efore the isolator on line conduct

The se$uence of o#eration while o#ening and closing acircuit%

While >#ening5 (i) >#en circuit !rea+er(ii) >#en isolator(iii) Close earthing switch

While Closing5 (i) >#en earthing switch(ii) Close isolator

(iii) Close circuit !rea+er

g


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Earthing switches


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'IGHTNING ARRESTERS The lightning arrester is a surge dierter and is used for the

#rotection of #ower system against the high oltage surges

It is connected !etween the lines and the earth and so diethe in coming high oltage wae to the earth%

If #rotection fails or is a!sent" lightning that stri+es the

electrical system introduces thousands of +iloolts that madamage the transmission lines" and can also cause seeredamage to the transformers and other electrical or electrondeices%


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TYPES OF LIGHTNING ARRESTER

13 STATION TY0E ARRESTER4 As distinguished !y their construction" !etter #rotectie characteristics and highercurrent ca#acity are used for the #rotection of su!station#ower transformer% We hae 1"A #ea+ 5 /%/ to '47+larger #ower station%'3 'INE TY0E ARRESTER5 This is used for the #rotectiondistri!ution transformers and some time small su!station7"A #ea+5 /%/ to 1'/+ rms for medium #ower station3. DISTRIBUTION TYPE ARRESTER: Are used #rimarily for mounting distri!ution transformer% We hae '"71"7 /%/+ rms for distri!ution or rural system%


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53 +A'+E TY0E ARRESTER5 Are commonly in more high #owered electrical system% It coof a series of non&linear resistor disc% -ale tarresters wor+ when e8cessie oltage causes#ar+ ga#s to touch" and the non&linear resis

carry the oltage into the ground%

'IGHTNING ARRESTER $AINTENANCE


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The maintenance test that may !e made on lightning

arresters with ,C oltage insulation resistance

measurement% 0ollowing is the generaliDed maintenance#rocedure for lightning arrester for conducting the insulatresistance test

% The test oltage is ,irect Current ty#e and is1%; times rateoltage of lightning%

At a #ressure of 1 - a##lied !etween each lie conducand earth for a #eriod of one minute the insulationresistance of H- installations shall !e at least 1 2ega ohmas s#eci:ed !y locally recogniDed standards !ody%

lightning arresters


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lightning arresters

SINGLE TYPE LA MOUNTED TYPE LA


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R23s also +nown as Load !rea+ Switches are switchgears


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R23s also +nown as Load !rea+ Switches are switchgearsused in #ractice in order to maintain o#timum continuity ofserice" !y #roiding a means of isolation at the origin of eaccircuit% As shown in the :gure !elow%

The R23 allows segregation of the faulty sections of the systeor remote switching control" to #resere continuity of alternatie circuits% The aim of this function is to isolate or discircuit" a##aratus" or an item of the system from the remainde#arts" so that the #ersonnel may carry out wor+ on the isola


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RING $AIN (NITS -R$(s* Ring main units are distri!ution load !rea+ switches used oltages u# to 4+ to serice feeder load areas incom#lement of feeder circuit !rea+ers%

Ring main units are either5 fused ring switches" unfused rinswitches" e8tensi!le oil switches and interconnector switchRing main units sere the following #ur#oses5 (a) *rea+ing rated load current% (!) 2a+ing rated load current%

(c) Carrying s#eci:ed short circuit current% R23s hae /no%s of switches (circuit !rea+ers or isolators L*S)%

TY0ES OF RING $AIN (NITS


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Ring main units is of indoor or out ty#e and can !made e8tensi!le on !oth sides% It consists of twounits of 11+" 9/A2.s continuously rated" tri#le

#ole non automatic" $uic+ !rea+" air !rea+" faultma+ing load !rea+ing switches" with associated!us!ars and connections for ma+ing controlling aincomingoutgoing 11+ feeder ca!le%

R23s can also !e #roided with two num!er load!rea+ switch with one num!er tee&o acuumcircuit !rea+er with #rotectie deices%


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SAFETY PRECAUTIONS IN SWITCHING RMUs

(1) Never open the first MU on ! fee"er #!rr$in% &ore th!

'A&ps.(') On#e ! $e!r t!*e +o#!+ o,t!%e to t!*e s!&p+e !n" #he

+eve+ in !n MU-

(3) Never s.it#h !n MU in ! n!rro. sp!#e / see* roo& f

es#!pe

(0) Never .e!r s+ippers or +oose s!n"!+s .hen s.it#hin% !

.e!r shoes-

() Never st!n" in front of the #!2+e / en" 2o .hen s.it

MU-


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R23s


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FEEDER 0I''AR


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0eeder #illar is an eectie electrical enclosure to#roide electrical serices for low oltage electricadistri!ution a##lications% It is designed as com#act

ro!ust for andalism #rotection% The metal enclosumade of sheet steel of minimum 'mm thic+ness"mounted on a steel !ase frame of minimum /mmthic+ness% Enclosure is suita!le for out door a##lica

0eeder #illars are distri!ution transformers ca!in

!oards for su##lying three #hase and single #hase at 417 and '4 res#ectiely in a safe economicaconenient way for o#erational and maintenance#ur#oses%


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0eeder #illar hae circuit arrangement which aways e8am#le of such are 5&

Two way

0our way

0ie way

Eight way%

0eeder #illar are Dinc s#ray and #ainted steelhousing to #reent corrosion !y the elements%

0eeder #illar


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0eeder #illar


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F(SES0use is a current interru#ting deice which !rea+s or o#enswhich it is inserted) !y fusing the element when the currencircuit e8ceeds a certain alue% 0use element or fuse wire iof the fuse which actually melts when an e8cessie currentthe circuit and thus isolates the faulty deice from the su#

0use lin+ is that #art of the fuse which needs re#lacement

fuse !lows out% The current rating is s#eci:ed !y manufactfusing current is de:ned as the minimum alue of the currewhich the fuse element or the fuse wire melts%

TY0ES OF F(SES

(1) Low oltage fuses


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(1) Low oltage fuses

(') High oltage fuses

Low oltage fuses can !e diided into two classeare semi&enclosed or rewira!le ty#e and totally encartridge ty#e

Rewira!le fuses is the most commonly used fusehouse wiring and small current circuits is the semienclosed or rewira!le fuse%

Cartridge ty#e fuse5 the fuse element is enclosed

totally enclosed container and is #roided with mecontact on !oth sides%

High oltage fuses are used u# to //+% They maem#loyed for oltage transformer #rotection or foru# to a!out 4A rated current on system u# to 1/

AD+ANTAGES OF F(SES


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(1) It is the chea#est ty#e of #rotection

(') It needs no maintenance%

(/) it interru#ts enormous short circuit current without

Bame" gas or smo+e% (4) The minimum ty#e of o#eration can !e made muc

than with circuit !rea+ers%

DISAD+ANTAGES OF F(SES

(1) Time is lost in rewiring or re#lacement of fuse afteo#eration%

(') ,iscrimination !etween fuses in series cannot !e ounless there is a considera!le dierence in the relatithe fuses concerned%

CONTACTOR


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A contactor is an electrically controlled switch useswitching a #ower circuit" similar to a relay e8#ecthigher current rating%

A contactor is controlled !y a circuit which has a lower #ower leel than the switch circuit% A contac

intended to interru#t a short circuit current% Contarange from those haing a !rea+ing current of seam#eres and '4 ,C to many +iloolts%


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Contactors are used to control electric motors" lighting" heca#acitor !an+s" thermal ea#orators and other electrical

O0ERATING 0RINCI0'E

3nli+e general #ur#ose relays6 c"tactors are designed todirectly connected to high current load deices% Relays ten

of lower ca#acity and are usually designed for !oth normaand normally o#en a##lications%


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,eice switching more than 17am#eres or in circmore than a few +ilowatt are usually called contac

When current #asses through the electromagnetmagnetic :eld is #roduced which attracts the moof the contactor%

Contactors are rated !y designed load current #er(#ole)" ma8imum fault with stand current" duty cylife e8#ectancy" oltage and coil oltage%


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A general #ur#ose motor control may !e suifor heay starting duty on large motors6 so&c

de:nite #ur#ose contactors are carefully adto such a##lications as air&conditioning com#motor starting%

Contactors are often used to #roide large liginstallations such as on oce !uilding or reta!uilding% To reduce #ower consum#tion in thecontactors are used" which hae two o#eratin

4ont!#tors


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4ont!#tors


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4. electrical switchgears.ppt

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