intoduction to swithgear.ppt

8/20/2019 INTODUCTION TO SWITHGEAR.ppt

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INTRODUCTIOINTRODUCTIO

NN

TOTOSWITCHGEARSSWITCHGEARS


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INTRODUCTIONINTRODUCTION

Switchgear is a generic term andincludes the entire range of switching

devices and their combination with

associated control, measuring,protecting and regulating equipment.


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INTRO-ctdINTRO-ctd

The assemblies of such devices andequipment with associated inter-

connections, accessories, enclosures

and supporting structures, intended inprinciple, for use in connection with

the generation, transmission,

distribution and conversion of electricenergy also form a switchgear.


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INTRO-ctdINTRO-ctd

We are all familiar with low voltageswitches and re-wireable fuses in ourhomes. switch is used for o!ening andclosing an electric circuit while a fuse isused for over-current and short-circuit

!rotection."ver# electric circuit needs a switchingdevice and a !rotective device. Theswitching and !rotective devices havebeen develo!ed in various forms. Thusswitchgear can be ta$en as a generalterm covering a wide range ofe%ui!ment concerned with the switching&!rotection and control of various

electrical "%ui!ments.


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INTRO-ctdINTRO-ctd

'imilarl#& switching and currentinterru!ting devices !la# a signi(cantrole in the modern electrical networ$&right from generating stations&

transmission sub stations at di)erentvoltages& distributionsub-stations and load centres. Theswitching device here is called a circuitbrea$er.

The circuit brea$er& along withassociated devices for !rotection&metering and control regulation& iscalled a switchgear.


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INTRO-ctdINTRO-ctd

switchgear has to !erform thefunctions of carr#ing& ma$ing andbrea$ing the normal load current li$ea switch. In addition& it has to !erformthe function of clearing the faultcurrent for which sensing devices li$ecurrent transformers& !otentialtransformers and various t#!es of

rela#s& de!ending on the a!!lication&are em!lo#ed.


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INTRO-ctdINTRO-ctd

There also has to be !rovision formetering& controlling and data&wherein innumerable devices areused for achieving the switchgear

function. Thus a switchgear caninclude a circuit brea$er& currenttransformers& !otentialtransformers& !rotective rela#s&

measuring instruments& switches&fuses&*C+s& surge arrestors& isolators andvarious associated e%ui!ment.


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N"C"''IT,N"C"''IT,

'witchgears are necessar# at ever#switching !oint in the !ower s#stem forthe reasons mentioned above. There

are several voltage levels and fault

levels between the generating stationsand (nal load !oints. ence in thevarious a!!lications& the re%uirements ofswitchgears var# de!ending on thelocation& ratings and local re%uirements.

+esides the su!!l# networ$& switchgearis re%uired in industrial wor$s&industrial !roects& domestic andcommercial buildings.


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'WIT/"R'WIT/"R

C0''I1ICTIONC0''I1ICTION'withgears are broadl# classi(ed into2*ain 'withgearsu3illiar# swithgears

*ain 'witchgears are the e%ui!mentconcerned with the !rocess of switching

andisolating circuits in a !ower s#stem. These are Circuit +rea$ers& Isolators4Disconnector or Disconnecting 'witch5&"arthing 'witches& 0oad 'witches 4Ring*ain Units5 and Contactors


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'WIT/"R'WIT/"R

C0''I1ICTIONC0''I1ICTION Auxiliary Switchgears are secondary or subsidiary equipment which assist the main switchgear

equipment in the control, measurement, protection

and fault-clearing process. They includes protective

devices (such as protective relays, ightning

arresters, feeder pillars and fuses!, sensing devices(ie instrument transformers!, control "compensation

devices4series inductive reactors& shunt inductive

reactors& series ca!acitive reactors shunt ca!acitive

reactors5 and auxiliary power supply devices li#e

tripping units (battery ban# $ charger!


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*ain 'withgears*ain 'withgears

Circuit breakers are mechanicalswitching devices& ca!able of ma$ing&carr#ing and brea$ing currents undernormal circuit conditions and also

ma$ing& carr#ing for a s!eci(ed timeand brea$ing currents under s!eci(edabnormal circuit conditions such asthose of a short circuit.

circuit brea$er is usuall# intended too!erate infre%uentl#& although somet#!es are suitable for fre%uento!eration.6


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*ain 'withgears*ain 'withgears

When a current is interru!ted& an arcis generated. This arc must becontained& cooled& and e3tinguishedin a controlled wa#& so that the ga!

between the contacts can againwithstand the voltage in the circuit.Di)erent circuit brea$ers usevacuum& air& insulating gas& or oil as

the medium the arc forms in.Di)erent techni%ues are used toe3tinguish the arc.


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*ain 'withgears*ain 'withgearsCircuit breaker always trip the circuit but open

contacts of breaker cannot be visible physicallyfrom outside of the breaker and that is why it is

recommended not to touch any electrical circuit

just by switching off the circuit breaker.

So for better safety there must be some

arrangement so that one can see open condition

of the section of the circuit before touching it.

Isolator is a mechanical switch which isolates apart of circuit from system as when required.

lectrical isolators separate a part of the system

from rest for safe maintenance works.


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I'O0TORI'O0TOR

An isolator - also called disconnector switch or simplydisconnector is basically a no-load switch design to

operate under no-load condition. They are generally

installed along with a circuit breaker and provide

isolation of a circuit for the purpose of maintenance,

especially on supply side of the circuit breaker. Isolator

opens only after the opening of the circuit breaker and

closes first before the C.B. Isolator is interlocked with

circuit breaker such that wrong operation is avoided.


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I'O0TORI'O0TORcontcont77

There are different types of isolators availabledepending upon system requirement such as Single Break Isolator

Double Break Isolator Pantograph type Isolator


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I'O0TORI'O0TOR


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I'O0TORI'O0TOR


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I'O0TORI'O0TOR


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I'O0TORI'O0TOR


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!antograph Isolator !antograph Isolator


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I'O0TORI'O0TOR

"ated #haracteristics $a%imum voltage &ielectric 'ithstand !ower (requency #ontinuous current !eak 'ithstand current

)peak *ssym+

Short-time 'ithstand current )sym+

#losing time Ice reaking #apability

$echanical perations oad interrupting current


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I'O0TOR

/ *a$er Name andaddress

/ T#!e

/ Designationnumber

/ 'erial number/ 1re%uenc#/ *a3imum 8oltage/ Continuous current/ llowable

continuous currentclass

/ 9ea$ withstand current/ 'hort-time withstand

current/ 'hort-time current

duration/ 0ightning im!ulse

withstand voltage 4+I05/ *echanical O!erations/ 0oad interru!ting

current

0ameplate &ata


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arthing switcharthing switch

An arthing switch is a device used to

discharged to earth any residual voltage

trapped on a line after it!s opening.

An arthing switch is normally connected

between the line conductor and earth."#ust before the isolator $on line

conductor


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arthing switcharthing switch

The se%uence of operation while opening andclosing a circuit.

&hile 'pening( "i) 'pen circuit breaker "ii) 'pen isolator

"iii) Close earthing switch

&hile Closing( "i) 'pen earthing switch

"ii) Close isolator

"iii) Close circuit breaker


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R.*.UR.*.UAn *.+. "*ing main nit) is a load breaker switch "B)

capable of making and breaking current under normal condition.They are capable of making but not breaking short circuit

current.

/0CTI'0 I0 A 1'&* 2IT*IBTI'0 3T+

Breaking rated current+aking rated current

+aking specific short-circuit current

Carrying specific short-circuit current

4enerally

5. /acilitates convenience looping distribution of electric

energy

6. 4ives operational fle7ibility to the 2istribution network

8. Improves voltage profile when the ring is fed at more than

one point.


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CTs & 8Ts and 'urgeCTs & 8Ts and 'urge

rrestorsrrestors Current Transformer - step-down currentsfor measurement, control 9 protection

:oltage Transformer - step-down voltages

for measurement, control 9 protection

urge Arrestor ;ightning Arrester -

discharge lightning and switching surges to earth

and control over voltages


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OT"R'OT"R' hunt reactor - control over voltages by providing reactive power

compensation

0eutral 4rounding *eactor - 4enerally provided to inereactors to facilitate Auto-reclosing Coupling capacitor or C:T - filter


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Than$ ,ou Than$ ,ou


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CIRCUIT BREAKERS


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ecure open and closed position


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Apart from the main functions, they are re%uired to fulfil the

physical re%uirements as follows(

> Behave as a good conductor during a closed position and as a

good isolator during an open position.

> Change from the closed to open position in a short period of

time.

> 2o not generate overvoltages during switching.

> ?eep high reliability during operation.


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INTRODUCTIONINTRODUCTIONComponents of


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INTRODUCTIONINTRODUCTION3 - Switching (

2uring operation of


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%&'%&T )'*A+*' T*%/0 %&'%&T )'*A+*' T*%/0

igh voltage circuit brea#ertechnology has change over the

years. 1ost utility systems are

having mix population of bul# oil,minimum oil, vacuum, air blast,and S23 circuit brea#ers

The S23 circuit brea#er has

become the current state of theart technology at transmissionvoltages of 456+v and above!.


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%&'%&T )'*A+*'%&'%&T )'*A+*'

T*%/0 T*%/0 owever, S23 gas has been identi7ed as a

greenhouse gas, and safety regulations arebeing introduced in many countries in orderto prevent its release into the atmosphere.

8acuum circuit brea#er has emerged as thedominant technology in the medium voltagerange due to its superior features such as

long contact life, lac# of maintenancerequirement, low operating energyrequirement and high reliability.


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Classifcation o CircuitClassifcation o Circuit

BreakersBreakersThere are quite a few ways toclassify the circuit brea#ers.owever, the most general way ofclassi7cation is on the basis of

medium used for the arc extinction.

ther bases for the classi7cation ofcircuit brea#ers are summari9ed in

the :ow chart on the next page.


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BreakersBreakers


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BreakersBreakers Based on Voltage

On the basis of the voltage levelsfor which the# are used& the circuitbrea$ers are classi(ed as listed in

table 4with corres!onding voltageranges of use5.

l if i i i


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BreakersBreakersBased on LocationCircuit brea$ers are& based u!on

where the# are located& classi(edas& indoor and outdoor t#!es.

*edium and low voltage brea$ersare categori:ed as Indoor circuitbrea$ers& whereas the circuitbrea$ers which have air as e3ternal

insulating medium are classi(ed asoutdoor circuit brea$ers.


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BreakersBreakers

Based on External DesinOutdoor circuit brea$ers can beidenti(ed as either dead tan$ or live tan$t#!e circuit brea$ers& from the !oint of

view of their !h#sical structural design.In the dead tan$ circuit brea$ers& theswitching device is located& with suitableinsulator su!!orts& inside a metallicvessel at ground !otential and (lled withinsulatingmedium.

Cl if i Ci i


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BreakersBreakers&n dead tan# circuit brea#ers, theincoming and outgoing conductorsare ta#en out through suitableinsulator bushings, and low voltage

type current transformers arelocated at lower end of both insulatorbushings, i.e. at the line side and theload side as shown below.


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BreakersBreakers&n live tan# circuit brea#ers, shownbelow, theinterrupter is located in an insulator

bushing, at

a potential above ground potential.The livetan# circuit brea#ers are cheaper

(with no

current transformer!, and require lessmounting space.


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Cl if i Ci iCl if ti Ci it


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BreakersBreakersBased on Interru!tin "edia The interru!ting media has been avital factor in the evolution of circuitbrea$ers. It dedicates the overall

design !arameters of the brea$er. The choice of air and oil& as theinterru!ting media& was !redominanttill late ;


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arc extinctionarc extinctionThe medium used for the arc extinction canbe;

il Air 8acuumSulphur exa:uoride (S23!

Accordingly, the circuit brea#ers may beclassi7ed into following categories(which willbe treated in detail in the next presentation!;

il %ircuit )rea#ers Air-blast %ircuit )rea#ersSulphur exa:uoride (S23! %ircuit )rea#ers

8acuum %ircuit )rea#ers


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&evelopment of #ircuit reakers&evelopment of #ircuit reakers


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R"C9R"C9


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View of bulk oil circuit breaker,


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Typical view of 36 kV !CB a"# Cro$$%$ectio" of i"terrupti"& c'a(ber Typical view of 36 kV !CB a"# Cro$$%$ectio" of i"terrupti"& c'a(ber


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Vacuu( i"terrupter


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Than$ ,ou Than$ ,ou

Nagode. "seun. Imeela.

Oil Circuit#BreakersOil Circuit#Breakers


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Oil Circuit#BreakersOil Circuit Breakersoil circuit-breakers are the most fundamental circuit-breakers

which were first developed in 5s. The first oil circuit-

breaker was developed and patented by #. 0. ?elman in the

nited tates. 'il has an e7cellent dielectric strength which

enables itself not only to be used as an interrupting medium

but also as insulation within the live parts. The interrupting

techni%ue of oil circuit-breakers is called self-e7tinguishingD,since the oil can produce a high pressure gas when it is

e7posed to heat resulting from arc. In other words, arc can be

cooled down by the gas produced proportional to arc energy.

2uring the arc interruption, the oil forms a bubble comprisingmainly hydrogen. It is found that arc burning in hydrogen gas

can be e3tinguished faster than other t#!es of

gases

intoduction to swithgear.ppt

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