U Breakers

8/18/2019 U Breakers

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Doble Engineering Company 1

Understanding Circuit Breakers

Basic Concepts


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Doble Engineering 2

Circuit Breakers

Ever since the time when electrical energy was firstused, there has been a need for a device to initiate orinterrupt the flow of current.

The methods used to achieve this interruption haveevolved through the years, from the time when thearc was merely stretched until it broke, to today,were sophisticated interrupters perform the sameoperation at greater voltages and with greaterefficiency.


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Doble Engineering 3

Basic Interruption

n C system is based in a !ine wave"n an C system, #reakers are the devices that

interrupt the voltagen C #reaker ob$ective is to break the current

flow in the circuit

nalogous to a domestic light switch.


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Doble Engineering %

#asic "nterruption &cont.'#asic "nterruption &cont.'

When a switch carrying ACcurrent opens, an arc forms

This arc strikes as the last metal-to-metal contact breaks

The arc is a conductorAs the moving contact movesaway from the stationary contactthe arc is stretched

The stretching and cooling willenable the arc to quench atcurrent zero subsequent to contactparting


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n a !ine wave, the voltage andcurrent cross zero twice each cycleAt these zero crossings the arce"tinguishes

The arc will remain e"tinguished ifthe dielectric between the contacts issufficient to withstand the voltage

The arc will be re-established if thedielectric between the contacts is not

sufficient to withstand the voltage


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Doble Engineering )



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Circuit Breakers

+hat is it ...

Circuit #reaker is a device for closing,maintaining and interrupting an electricalcircuit between separable contacts, under

normal &load' and abnormal &fault' conditions.


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Circuit Breakers

ow does it work /

n C #reaker waits for current 0ero "t attempts to prevent arc re1ignition

Commutes plasma by removing energy


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Circuit Breakers

Transient #ecovery $oltage %T#$&oltage generated by the system during interruption

process

t current 4ero, when current is interrupted, the systemoscillates in accordance to its natural fre5uencyThis voltage stresses the gap insulation

u6iliary devices are used to modify the T7 when the

basic interrupter of the circuit breaker does not meet theinterruption re5uirements


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Doble Engineering 89

Circuit Breakers

u6iliary Devices"nsertion 7esistors

: To reduce voltage transients : To reduce the severity of the T7 : To damp oscillation

Capacitors : !hunt Capacitors; for initial rate of rise of transient

voltage :


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Circuit Breakers

=ife; 391%9 years

>perating time; 8(139 minutes

bnormal conditions; 391)9 seconds


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Circuit Breakers Types

Two #asic Types;

Dead Tank;The enclosure that surrounds the breaker contacts iselectrically at ground potential. The breaker mechanismand tank are at the same potential

=ive Tank

The enclosure that surrounds the breaker contacts is not atground potential. The breaker mechanism is separatedfrom the interrupters by a column


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Circuit Breakers Types (cont.)

?ay be;perated

: ?echanism operates all three phases together !ingle @ole >peration

: "ndependent mechanism for each phase

!ingle @ole >peration are used for higher oltages andneed to employ a phase disagreement circuit


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Doble Engineering 8%

Circuit Breakers Classification

"nterruption in ir

"nterruption in >il"nterruption in acuum

"nterruption in !A)


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Doble Engineering 8(

Interruption in Air

ir ?agnetic Circuit #reakersThe interruption takes place in air under the

influence of a magnetic field at atmospheric pressure

ir #last Circuit #reakersThe interruption takes place in a blast of air


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8)

Interruption in Oil

#ulk >il Circuit #reakers &also called dead tank'The interruption takes place in oil. The contacts areimmersed in oil which serves as arc 5uencher.

?inimum >il &also called live tank'The interruption takes place in oil in the same manner as

the bulk type. The difference is the amount of oil. Therelatively small oil container is insulated from ground.

>il Circuit #reakers are essentially a hydrogen interrupter.


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Doble Engineering 8*

Interruption in Vacuum

The interruption takes place in a acuumB essel &interrupter', which is hermetically

sealed

rcing is established within the interrupter

by separation of the contacts


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Doble Engineering 8-

Interruption in S !

The interruption takes place in a !ulfure6aflouride &!A)' medium, which has e6cellent

dielectric characteristics.The !A) #reakers are classified as follows;

Double pressure

@uffer type!elf e6tinguishing


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Doble Engineering 8

Circuit S"itc#ers

Combine the function of a circuit breaker and adisconnect switch

They incorporate an interrupter and a knife blade

They employ : !A) : acuum

Cost effective alternative to #reaker ?ore limited in application


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Circuit S"itc#ers (cont.)

8. #oth blade and

interrupter are closed,carrying current


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2. +hen activated, theinterrupter opens,

braking the current,while the blade is stillclosed


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3. The blade opens for fullvisual confirmation ofcircuit isolation


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%. pon closing, the blade

is rotated closed, withinterrupter still open


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(. The final closing of the blade activates themechanism, closing theinterrupter

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