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  • 8/7/2019 ps2 assignment


    A circuit breaker is an automatically operated electrical switch designed to protect an electrical

    circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition

    and, by interrupting continuity, to immediately discontinue electrical flow. Unlike afuse, which operates

    once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to

    resume normal operation. Circuit breakers are made in varying sizes, from small devices that protectan individual household appliance up to large switchgear designed to protect high voltage circuits

    feeding an entire city.



    1 Origins

    2 Operation

    3 Arc interruption

    4 Short circuit current

    5 Standard current ratings

    6 Types of circuit breaker

    o 6.1 Low voltage circuit breakers

    o 6.2 Magnetic circuit breaker

    o 6.3 Thermal magnetic circuit breaker

    o 6.4 Common trip breakers

    o 6.5 Medium-voltage circuit breakers

    o 6.6 High-voltage circuit breakers o 6.7 Sulfur hexafluoride (SF6) high-voltage circuit-breakers

    7 Other breakers

    8 See also

    9 References

    10 External links


    All circuit breakers have common features in their operation, although details vary substantially

    depending on the voltage class, current rating and type of the circuit breaker.

    The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done

    within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged

    with pilot devices to sense a fault current and to operate the trip opening mechanism. The

    trip solenoid that releases the latch is usually energized by a separate battery, although some high-

    voltage circuit breakers are self-contained with current transformers, protection relays, and an internal

    control power source.

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    Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some

    mechanically-stored energy (using something such as springs or compressed air) contained within the

    breaker is used to separate the contacts, although some of the energy required may be obtained from

    the fault current itself. Small circuit breakers may be manually operated; larger units have solenoids to

    trip the mechanism, and electric motors to restore energy to the springs.The circuit breaker contacts must carry the load current without excessive heating, and must also

    withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or

    copper alloys, silver alloys, and other materials. Service life of the contacts is limited by the erosion

    due to interrupting the arc. Miniature and molded case circuit breakers are usually discarded when the

    contacts are worn, but power circuit breakers and high-voltage circuit breakers have replaceable


    When a current is interrupted, an arc is generated. This arc must be contained, cooled, and

    extinguished in a controlled way, so that the gap between the contacts can again withstand the

    voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium in

    which the arc forms. Different techniques are used to extinguish the arc including:

    Lengthening of the arc

    Intensive cooling (in jet chambers)

    Division into partial arcs

    Zero point quenching (Contacts open at the zero current time crossing of the AC waveform,

    effectively breaking no load current at the time of opening. The zero crossing occurs at twice the

    line frequency i.e. 100 times per second for 50Hz and 120 times per second for 60Hz AC)

    Connecting capacitors in parallel with contacts in DC circuits

    Finally, once the fault condition has been cleared, the contacts must again be closed to restore power

    to the interrupted circuit.

    [edit]Arc interruption

    Miniature low-voltage circuit breakers use air alone to extinguish the arc. Larger ratings will have

    metal plates or non-metallic arc chutes to divide and cool the arc. Magnetic blowout coils deflect the

    arc into the arc chute.

    In larger ratings, oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil

    through the arc. [2]

    Gas (usually sulfur hexafluoride) circuit breakers sometimes stretch the arc using a magnetic field,

    and then rely upon the dielectric strength of the sulfur hexafluoride (SF6) to quench the stretched arc.

    Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact

    material), so the arc quenches when it is stretched a very small amount (

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    Air circuit breakers may use compressed air to blow out the arc, or alternatively, the contacts are

    rapidly swung into a small sealed chamber, the escaping of the displaced air thus blowing out the arc.

    Circuit breakers are usually able to terminate all current very quickly: typically the arc is extinguished

    between 30 ms and 150 ms after the mechanism has been tripped, depending upon age and

    construction of the device.[edit]Short circuit current

    Circuit breakers are rated both by the normal current that are expected to carry, and the maximum

    short-circuit current that they can safely interrupt.

    Under short-circuit conditions, a current many times greater than normal can exist (see maximum

    prospective short circuit current ). When electrical contacts open to interrupt a large current, there is a

    tendency for an arc to form between the opened contacts, which would allow the current to continue.

    This condition can create conductive ionized gasses and molten or vaporized metal which can cause

    further continuation of the arc, or creation of additional short circuits, potentially resulting in theexplosion of the circuit breaker and the equipment that it is installed in. Therefore, circuit breakers

    must incorporate various features to divide and extinguish the arc.

    In air-insulated and miniature breakers an arc chute structure consisting (often) of metal plates or

    ceramic ridges cools the arc, and magnetic blowout coils deflect the arc into the arc chute. Larger

    circuit breakers such as those used in electrical power distribution may use vacuum, an inert gas such

    as sulphur hexafluoride or have contacts immersed in oil to suppress the arc.

    The maximum short-circuit current that a breaker can interrupt is determined by testing. Application of

    a breaker in a circuit with a prospective short-circuit current higher than the breaker's interrupting

    capacity rating may result in failure of the breaker to safely interrupt a fault. In a worst-case scenario

    the breaker may successfully interrupt the fault, only to explode when reset.

    Miniature circuit breakers used to protect control circuits or small appliances may not have sufficient

    interrupting capacity to use at a panelboard; these circuit breakers are called "supplemental circuit

    protectors" to distinguish them from distribution-type circuit breakers.

    [edit]Standard current ratings

    International Standard IEC 60898-1 and European Standard EN 60898-1 define the rated current I n of

    a circuit breaker for low voltage distribution applications as the current that the breaker is designed to

    carry continuously (at an ambient air temperature of 30 C). The commonly-available preferred values

    for the rated current are 6 A, 10 A, 13 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A, 63 A, 80 A and 100

    A[3] (Renard series , slightly modified to include current limit of BritishBS 1363 sockets). The circuit

    breaker is labeled with the rated current in amperes , but without the unit symbol "A". Instead, the

    ampere figure is preceded by a letter "B", "C" or "D" that indicates the instantaneous tripping current ,

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    I n

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    I n 6

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    above H

    I n up to and inc lud ing X

    I n f or per iods in the order of tens of seconds .

    P or the pro tec tion of loads such as sem iconduc tor dev ices or measur ing c ircu its us ing curren t

    trans f ormers .

    [ed it]Y U pes of circu it breaker

    P ron t pane l of a E H

    @ F

    A a ir circu it breaker manu f ac tured by ABB. Y h is low vo ltage power circu itbreaker can be withdrawn f rom its hous ing f or serv icing . Y r ip charac ter is tics are con figurab le viaG IPsw itches on the f ron t pane l.

    ` any d iff eren t class ifica tions of c ircu it breakers can be made , based on the ir f ea tures such as vo ltage

    class , cons truc tion type , in terrup ting type , and s truc tura l f ea tures .

    [ed it]L ow volta g e a ircu it b reakers

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    L ow vo ltage c

    less than d e e e

    V Af ) types are common in domes tic , commerc ia l and indus tr ia l

    app lica tion , and inc lude :

    g h


    g inia ture h

    ircu it Breaker)ra ted curren t no t more than d e e


    r ip charac ter is tics norma lly

    no t ad jus tab le .i

    herma l or therma lp magne tic opera tion . Breakers illus tra ted above are in th is

    ca tegory .

    g h h


    g olded h

    ase h

    ircu it Breaker)ra ted curren t up to q r e e


    herma l or therma lp magne tic

    opera tion .i

    r ip curren t may be ad jus tab le in larger ra tings .

    L ow vo ltage power circu it breakers can be moun ted in mu ltip tiers in L V sw itchboards

    or sw itchgear cab ine ts .i

    he charac ter is tics of LV circu it breakers are g iven by in terna tiona l s tandards such as IEh

    s t u .i

    hese circu it breakers are often ins ta lled in draw-ou t enc losures tha t a llow remova l and interchange

    withou t disman tling the sw itchgear .

    L arge low-vo ltage mo lded case and power circu it breakers may have e lec tr ica l mo tor opera tors ,

    a llow ing them to be tr ipped c

    opened) and c losed under remo te con trol.i

    hese may f orm par t of

    an au toma tic trans f er sw itch sys tem f or s tandby power .

    L ow-vo ltage circu it breakers are a lso made f or direc t-curren tc



    ) app lica tions , f or examp le v h

    supp lied f or subway lines . Spec ia l breakers are requ ired f or direc t curren tbecause the arc does no t

    have a na tura l tendency to go ou t on each ha lf cyc le as f or a lterna ting curren t. A direc t curren t circu it

    breaker willhave b low-ou t co ils wh ich genera te a magne tic fie ld tha t rap idly s tre tches the arc when

    in terrup ting direc t curren t.

    Sma ll circu it breakers are e ither ins ta lled direc tly in equ ipmen t, or are arranged in abreaker pane l.

    Pho to of ins ide of a circu it breaker

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    The 10 ampere DIN rail-mounted thermal-magnetic miniature circuit breaker is the most common style

    in modern domestic consumer units and commercial electrical distribution boards throughout Europe.

    The design includes the following components:

    1. Actuator lever - used to manually trip and reset the circuit breaker. Also indicates the status of

    the circuit breaker (On or Off/tripped). Most breakers are designed so they can still trip even

    if the lever is held or locked in the "on" position. This is sometimes referred to as "free trip" or

    "positive trip" operation.

    2. Actuator mechanism - forces the contacts together or apart.

    3. Contacts - Allow current when touching and break the current when moved apart.

    4. Terminals

    5. Bimetallic strip.

    6. Calibration screw - allows the manufacturer to precisely adjust the trip current of the device

    after assembly.7. Solenoid

    8. Arc divider/extinguisher [edit]M a w netic circuit breaker

    M agnetic circuit breakers use a solenoid (electromagnet ) whose pulling force increases with

    the current. Certain designs utilize electromagnetic forces in addition to those of the solenoid. The

    circuit breaker contacts are held closed by a latch. As the current in the solenoid increases beyond

    the rating of the circuit breaker, the solenoid's pull releases the latch which then allows the contacts to

    open by spring action. Some types of magnetic breakers incorporate a hydraulic time delay feature

    using a viscous fluid. The core is restrained by a spring until the current exceeds the breaker rating.During an overload, the speed of the solenoid motion is restricted by the fluid. The delay permits brief

    current surges beyond normal running current for motor starting, energizing equipment, etc. Short

    circuit currents provide sufficient solenoid force to release the latch regardless of core position thus

    bypassing the delay feature. Ambient temperature affects the time delay but does not affect the

    current rating of a magnetic breaker.

    [edit]Th erma l ma x netic circuit breaker

    T hermal magnetic circuit breakers , which are the type found in most distribution boards, incorporate

    both techniques with the electromagnet responding instantaneously to large surges in current (short

    circuits) and the bimetallic strip responding to less extreme but longer-term over-current conditions.

    [edit]Common trip breakers

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    y hree po le common tr ip breaker f or supp lying a three-phase dev ice . y h is breaker has a A ra ting

    hen supp lying a branch circu it with more than one live conduc tor , each live conduc tor mus t be

    pro tec ted by a breaker po le . y o ensure tha t a ll live conduc tors are in terrup ted when any po le tr ips , a

    common tr ip" breaker mus t be used . y hese may e ither con ta in two or three tr ipp ing mechan isms

    within one case , or f or sma ll breakers , may ex terna lly tie the po les toge ther via the ir opera ting

    hand les . y wo po le common tr ip breakers are common on


    vo lt sys tems where

    vo lt loads

    inc lud ing ma jor app liances or f ur ther dis tr ibu tion boards) span the two live wires . y hree-po le common

    tr ip breakers are typ ica lly used to supp ly three-phase e lec tr ic power to large mo tors or f ur ther

    d is tr ibu tion boards .

    y wo and f our po le breakers are used when there is a need to d isconnec t the neu tra l wire , to be sure

    tha t no curren t can flow back through the neu tra l wire f rom o ther loads connec ted to the same ne twork when peop le need to touch the wires f or ma in tenance . Separa te c ircu it breakers mus t never

    be used f or disconnec ting live and neu tra l, because if the neu tra l ge ts d isconnec ted wh ile the live

    conduc tor s tays connec ted , a dangerous cond ition ar ises : the circu it willappear de-energ i ed

    app liances willno t work) , bu t wires wills tay live and

    s willno t tr ip if someone touches the live

    wire because

    s need power to tr ip) . y h is is why on ly common tr ip breakers mus t be used when

    sw itch ing of the neu tra lwire is needed .

    [ed it]Med iu m-v olta g e c ircu it reakers

    ed ium-vo ltage circu it breakers ra ted be tween and

    kV may be assemb led in to me ta l-enc losed

    sw itchgear line ups f or indoor use , or may be ind ividua l componen ts ins ta lled ou tdoors in a subs ta tion . Air-break circu it breakers rep laced oil-filled un its f or indoor app lica tions , bu t are now

    themse lves be ing rep laced by vacuum circu it breakers up to abou t

    kV). L ike the high vo ltage

    circu it breakers descr ibed be low , these are a lso opera ted by curren t sens ing

    pro tec tive re lays opera ted through curren t trans f ormers . y he charac ter is tics of V breakers are g iven

    by in terna tiona l s tandards such as IE

    . ed ium-vo ltage circu it breakers near ly a lways use

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    separa te curren t sensors and pro tec tive re lays , ins tead of re lying on bu ilt-in therma l or magne tic

    overcurren t sensors .

    ed ium-vo ltage circu it breakers can be c lass ified by the med ium used to ex tingu ish the arc :

    Vacuum circu it breakerW ith ra ted curren t up to

    A, these breakers in terrup t the curren t by crea ting and ex tingu ish ing the arc in a vacuum con ta iner . hese are genera lly app lied f or

    vo ltages up to abou t

    , V,[

    ] wh ich corresponds rough ly to the med ium-vo ltage range of

    power sys tems . Vacuum circu it breakers tend to have longer lif e expec tanc ies be tween overhau l

    than do a ir circu it breakers .

    Air c ircu it breakerRa ted curren t up to , A. r ip charac ter is tics are often f ully ad jus tab le

    inc lud ing con figurab le tr ip thresho lds and de lays . sua lly e lec tron ica lly con trolled , though some

    mode ls are m icroprocessor con tro lled via an in tegra l e lec tron ic tr ip un it. ften used f or ma in

    power dis tr ibu tion in large indus tr ia l plan t, where the breakers are arranged in draw-ou t

    enc losures f or ease of ma intenance .

    S j k circu it breakers ex tingu ish the arc in a chamber filled with su lf ur hexa fluor ide gas .

    ed ium-vo ltage circu it breakers may be connec ted in to the circu it by bo lted connec tions to bus bars

    or wires , espec ia lly in ou tdoor sw itchyards . ed ium-vo ltage circu it breakers in sw itchgear line-ups are

    often bu iltwith draw-ou t cons truc tion , a llow ing the breaker to be removed withou t dis turb ing the

    power circu it connec tions , us ing a mo tor-opera ted or hand-cranked mechan ism to separa te the

    breaker f rom its enc losure .

    [ed it]High-v olta g e c ircu it l

    reakers Ma i m ar ti n l o : Hi

    -v lt age wit n


    kV S live tank circu it breakers

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    kV bu lk o il circu it breaker

    Elec tr ica l power transm iss ion ne tworks are pro tec ted and con tro lled by high-vo ltage breakers .z


    de fin ition of h i g h v { lt age var ies bu t in power transm iss ion work is usua lly though t to be | } . kV or

    h igher , accord ing to a recen t de finition by the Interna tiona l Elec trotechn ica l ~ omm iss ion

    IE~ ). igh-

    vo ltage breakers are near ly a lways so leno id-opera ted , with curren t sens ing pro tec tive re lays opera ted

    through curren t trans f ormers . In subs ta tions the pro tec tive re lay scheme can be comp lex ,pro tec ting

    equ ipmen t and buses f rom var ious types of over load or ground /ear th f au lt.

    igh-vo ltage breakers are broad ly class ified by the med ium used to ex tingu ish the arc .

    Bu lk oil

    inimum oil

    Air b las t



    Some of the manu f ac turers are ABB,


    enera l Elec tr ic) ,

    avr ida Elec tr ic, Als tom , itsub ish i

    Elec tr ic, Pennsy lvan ia Breaker , Siemens ,

    osh iba , Kon ar

    VS, B

    EL ,

    L , Square

    Schne ider

    Elec tr ic) .

    ue to env ironmen ta l and cos t concerns over insu la ting o il sp ills , mos t new breakers use S gas to

    quench the arc .

    ircu it breakers can be class ified as liv e t ank , where the enc losure tha t con ta ins the break ing

    mechan ism is a t line po ten tia l, or dead t ank with the enc losure a t ear th po ten tia l. igh-vo ltage A

    circu it breakers are rou tine ly ava ilab le with ra tings up to

    kV. KVbreakers are like ly to come

    in to marke t very soon .

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    H igh-vo ltage circu it breakers used on transm iss ion sys tems may be arranged to a llow a s ing le po le of

    a three-phase line to tr ip , ins tead of tr ipp ing a ll three po les ; f or some classes of f au lts this improves

    the sys tem s tab ility and ava ilab ility.

    [ed it]S ulfur h exafluor ide (SF 6) high-v olta g e c ircu it- reakers

    Ma i n ar ti

    l e : S


    r h exa fl

    r i de

    i rcu it


    A su lf ur hexa fluor ide circu it breaker uses con tac ts surrounded by su lf ur hexa fluor ide gas to quench

    the arc .

    hey are mos t often used f or transm iss ion- leve l vo ltages and may be incorpora ted in to

    compac t gas- insu la ted sw itchgear . In co ld clima tes , supp lemen ta l hea ting or de-ra ting of the circu it

    breakers may be requ ired due to lique f ac tion of the S gas .

    [ed it] ther breakers

    he f ollow ing types are descr ibed in separa te ar ticles .

    Breakers f or pro tec tions aga ins t ear th f au lts too sma ll to tr ip an over-curren t dev ice :

    Res idua l-curren t dev ice RCD , f ormer ly known as a res i dua l curren t c i rcu it

    reaker )

    de tec ts curren t imba lance , bu t does no t prov ide over-curren t pro tec tion .

    Res idua l curren t breaker with over-curren t pro tec tion RC B

    ) comb ines the f unc tions of an

    RCD and an

    CB in one package . In the

    nited Sta tes and Canada , pane l-moun ted dev ices

    tha t comb ine ground ear th) f au lt de tec tion and over-curren t pro tec tion are ca lled round

    au lt C ircu it Interrup ter CI) breakers ; a wa ll moun ted ou tle t dev ice prov id ing ground f au lt

    de tec tion on ly is ca lled a I.

    Ear th leakage c ircu it breaker EL CB) h is de tec ts ear th curren t direc tly ra ther than

    de tec ting imba lance .

    hey are no longer seen in new ins ta lla tions f or var ious reasons . Au torec loser A type of circu it breaker wh ich closes aga in a fter a de lay . hese are used on

    overhead power d is tr ibu tion sys tems , to preven t shor t dura tion f au lts f rom caus ing sus ta ined

    ou tages .

    Po lysw itch po lyf use) A sma ll dev ice common ly descr ibed as an au toma tica lly rese tting f use

    ra ther than a circu it breaker .[ed it]See a lso

    Electronics portal

    Power sys tem pro tec tion

    Res idua l curren t dev ice

    Ear th leakage circu it breaker

    Ear th ing sys tem

    Domes tic AC power plugs and socke ts

    Arc- f au lt circu it in terrup ter

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    Insulation monitoring device

    Circuit Total Limitation (CTL)

    Network protector

    Circuit breaker panel


    1. ^ Robert Friedel and Paul Israel, E dison's E lectric Light: Biography of an In ention , Rutgers

    University Press, New Brunswick New Jersey USA,1986 ISBN 0-8135-1118-6 pp.65-66

    2. ^ B. M. Weedy, E lectric Po er Systems Second E dition , John Wiley and Sons, London,

    1972, ISBN 0471924458 pp. 428-430

    3. ^

    4. ^ Few manufacturers offer now a single-bottle vacuum breaker rated up to 72.5 kV and even

    145 kV.

    See Electrical Engineering in Japan, vol 157 issue 4 pages 13-23

    BS EN 60898-1. Electrical accessories Circuit breakers for over-current protection for

    household and similar installations. British Standards Institution, 2003.



    Edgar Dullni, Harald Fink, Christian Reuber

    ABB Calor Emag Mittelspannung GmbH

    Bahnstrae 39-47, P.O. Box 1220, D-40832 Ratingen (Germany)

    Tel : +49 2102 12-1281 Fax : +49 2102 12-1933 E-mail: [email protected]


    Vacuum circuit-breakers have obtained a high level of

    performance, reliability and safety. This is mostly owed to

    the advantages of current interruption in vacuum. However, the design of the mechanical drive, whichhas already been applied e.g. in minimum oil-breakers, has

    hardly been changed. With the introduction of an actuator

    with permanent magnetic limit positions and electromagnetically controlled motion, the nextgeneration of

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    vacuum circuit-breakers is launched promising an increase in reliability and endurance. The operationof the

    circuit-breaker is controlled by an electronic device implementing interlocking, signaling, releases andselfdiagnosis. The electronic control and supply requires a

    somewhat different approach to applications compared

    with a conventional circuit-breaker. The experience with

    frequent operations reaching 100000 CO is promising.


    Innovations in vacuum switching technology have constantly increased the efficiency of vacuumcircuit-breakers

    while at the same time reducing their external dimensions.

    The mechanical operating mechanisms initially used,

    familiar in the context of minimum oil breakers, were

    made more compact and adapted to suit the lower energy

    requirement of vacuum interrupters. The large number of

    parts required to control the function of a purely mechanical operating mechanism however remaineda disadvantage. It will be remembered that the possibility of a failure

    increases in proportion to the number of individual parts.

    The failure statistics therefore predominantly comprise

    mechanical defects.

    Even 20 years ago, attention was devoted to electromechanical operating devices for vacuuminterrupters [1,2].

    They were however only used with contactors which required extremely frequent switching. Thedisadvantages of

    a high power consumption and the necessary mechanical

    control and electrical switching components for the coil

    current opposed their further spread. Furthermore, mechanical latching in the limit positions wasrequired. Irrespective of this, electromagnetic operating mechanisms

    ideally match the requirements of vacuum interrupters:

    both are characterized on the one hand by a short stroke (8

    - 12 mm), and on the other hand - in the closed position -

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    by a large force requirement (2000 to 4000 N per phase)

    and a large force capability respectively.

    By means of a special combination of electric and permanent magnets [3,4] it was possible to avoidthe high power

    requirement for switching and the disadvantages of a mechanical latching system for the limitpositions. The vacuum interrupter is held in the open and close positions by

    the force of a permanent magnet without any electrical

    energy. As a result, the operating mechanism is considerably simpler in structure than a conventionalmechanical

    system (figure 1). With the drastic reduction in the number

    of parts, the susceptibility to failures is significantly lower,

    and therefore no maintenance of the operating mechanism

    is necessary [5,6].

    Figure 1: View of the VM1 circuit-breaker

    A further advantage of the new device is the implementation of an electronic power control withuniversal power

    supply. Coil current switching, interlocking, signaling and

    also self-diagnosis is provided by a specially designed

    control unit. These facilities can only be implemented in

    conventional mechanisms by complex wiring of auxiliary

    switches if at all. The need for auxiliary switches operated

    by the device is obviated by the use of inductive proximity

    sensors, which indicate the open and close positions without physical contact and without mechanicalmoving parts.PERMANENT MAGNET SWITCHING PRINCIPLE

    A conventional stored energy spring mechanism has a

    large number of mechanical components: typically around160, without standardized parts such as screws. The magnetic operating mechanism, in contrast, issignificantly

    simpler (figure 2). Apart from the moving contact in the

    vacuum interrupter itself, it consists merely of the link rod

    with contact pressure spring, a welded lever shaft 1 and

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    the permanent magnet actuator 3-6. The number of parts

    has been reduced to less than 40%.

    Figure 2: Section of the operating mechanism and pole part of the circuitbreaker

    1 Lever shaft 5 Plunger

    2 Proximity sensors 6 Opening coil

    3 Closing coil 7 Emergency manual opening

    4 Permanent magnets

    Figure 2 shows a section of such an actuator. The figure

    shows the fixed laminated iron core, the permanent magnets 4, the moving plunger in steel 5 andcoils for closing

    3 and opening 6.The magnetic field lines drawn in figure 3 help to explain

    the function of the actuator. In the position shown, the

    plunger at the "top" (open position) together with the iron

    core forms a path of low magnetic resistance for the field

    of the permanent magnets. In contrast, the large gap at the

    bottom of the plunger represents a high magnetic resistance. The field lines therefore run almost

    exclusivelythrough the end of the plunger being in contact with the

    core. The high concentration of field lines originating

    from the permanent magnets produces a large attracting

    force at this point. This attracting force is transmitted via

    the lever shaft (part 1 in figure 2) directly onto the contacts of the vacuum interrupter.




    Figure 3: Distribution of the magnetic field lines

    a) in the open position;

    b) shortly before the start of the motion;

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    c) after the end of the motion and before switching off the coil-currentThe coils are required for switching. Figure 3b illustrates

    the closing operation: the additional magnetic energy of

    the lower coil compensates for the high magnetic resistance of the gap, directing the field lines moreand more

    towards the lower path. The retaining force at the "top"

    declines, while the attraction at the "bottom" increases.

    When a certain level of current in the coil is exceeded, the

    plunger moves. Figure 3b is an instantaneous representation of the field lines shortly before theplunger starts to

    move. When the final position is securely reached, as in

    figure 3c, the remaining current in the coil improves the

    latching process. The combination of permanent magnetic

    flux and electromagnetic flux leads to a very high force

    that damps out mechanical oscillations very effectively.

    Some milliseconds later, the coil current is switched off.

    The field line distribution is then similar to that in figure

    3a, but this time with the plunger in the other limit position. Here, the closed position of the vacuum-interrupter

    contacts and the charged contact springs are latched with

    the static hold-force that is generated only by the permanent magnets. Current in the coils is notrequired as long

    as the circuit-breaker shall stay in this position.

    Emergency manual opening operations are also possible

    using a special crank. The crank engages directly with the

    armature (7 in figure 2), and thus bypasses all intermediate transmission components.The function of the actuator can be described as that of a

    bistable position switch which requires no mechanical

    control or latching functions. With such a system, 100,000

    operating cycles can easily be reached with only minor

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    maintenance. Therefore, the new circuit-breaker is extremely interesting for applications comprisingfrequent

    switching e.g. in paper mills and arc furnaces. Apart from

    the conducted endurance tests, importance was attached to

    long-term durability. The permanent magnets in neodymium-iron-boron (NdFeB) are not only chosenbecause of

    their high permeability, but also because of their high

    stability against demagnetization and their low aging [4].


    The electronic power supply and control unit for the circuit-breaker has to fulfil all the functions familiar from

    conventional mechanical operation mechanisms. In addition it provides and monitors the energy for switching the

    actuator (figure 4).

    A power supply 3 with an input voltage range of either 20

    to 66 V DC (20 to 48 V AC) or 93 to 375 V DC (93 to 265

    V AC) provides a constant operating voltage of 80 V,

    independently of the stability and quality of the auxiliary

    voltage supplied. Time-consuming adjustment of the

    equipment in the breaker to match the customers supply

    voltages is therefore no longer necessary. Undervoltage

    and overvoltage have no effect on switching times.

    Figure 4: Block diagram of the control electronics

    1 Opening and closing coils 5 Proximity sensors

    2 Storage capacitor 6 On and off button and readiness

    3 Power pack indicator

    4 Power semiconductors

    An electrolytic capacitor provides the surge power of up to

    2600 W required for energizing the opening and closing

    coils 1 in the actuator. It stores the electrical energy of less

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    than 200 J for a complete O-CO operating cycle. After

    such an operating cycle, the capacitor recharges within

    less than 10 s with a peak current of max. 2 A.

    Power semiconductors, in this case a combination of

    MOSFET transistors and thyristors, control the current for

    switching the actuator coils. The switching voltage induced by the inductivity of the coils oninterruption of the

    current are reduced by parallel free-wheeling diodes to

    such an extent that they have no further influence on the

    semiconductor components. Generous dimensioning of the

    components ensures a maximum of quality and long life,especially compared to conventional electromechanical

    relays. The MTBF


    of the electronic control unit, including the power supply, results in a value of 62.5 years (assumingan ambient temperature of 40C).

    A field programmable gate array (FPGA) controls the

    circuit-breaker. Switching commands are only executedtaking account of the switch position, which is detected by

    two inductive proximity sensors, and the charging condition of the storage capacitor. In the openposition, for

    example, there must be sufficient charge available for a

    complete CO switching operation. The controller blocks a

    closing operation, if an opening command is active at the

    same time. It also prevents a second closing operation, if

    an opening operation has been performed while a closing

    command is active. The proximity sensors detect impermissible intermediate positions, e.g. failure toreach a limit

    position, and signal these.

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    Mean Time Between Failures

    =/ 24....60V AC/DC or










    = 110....240V AC/DC

    CB Close (OCS)

    CB Open (OCS)

    CB Open (CCS)

    Block Open (CCS)

    CB Open (OCS)

    CB is ON (NOS)

    CB is OFF (NOS)

    CB trips (NOS)


    CB READY (NCS)Five inputs and five outputs, which are electrically isolated

    for 2.5 kV, form the interface to a panel or station automation system. The open circuit inputs acceptpulses from

    48 to 250 V AC/DC. Therefore, there is no need of an

    adaptation to the different requirements of customers

    minimizing co-ordination problems. The inputs are:

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    1. Close the CB (Open Circuit System; OCS)

    2. Open the CB (OCS)

    3. Open the CB (Closed Circuit System; CCS)

    4. Block the closing of the CB (CCS)

    5. 2


    Open CB (OCS)

    An OCS means here that voltage has to be applied for an

    action, while for CCS an action takes place when voltage

    is removed.

    Input 4 can be used with a circuit-breaker on a withdrawable unit. Closing should only be possible inthe terminal

    positions of this unit. In any intermediate position, the

    auxiliary switches in the withdrawable unit interrupt the

    feeding of this input, so that closing is impossible.

    Input 5 can be used for a redundant tripping circuit.

    For the monitoring of the device, five output-channels are


    1. CB is ON (Normally Open Contact; NOC)

    2. CB is OFF (NOC)

    3. CB is tripping (wipe-contact; NOC)

    4. CB is READY (NOC)

    5. CB is READY (Normally Closed Contact; NCC)

    E.g. for output 1, NOC means that this contact is only

    closed when the signal CB is ON is true. The contact of

    output 3 is closed for about 40ms during tripping.

    Output 4 is closed when the following parameters are


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    Internal supply voltage is available

    The internal control of the FPGA (watchdog) is


    The position of the CB has been detected and is plausible

    The voltage level of the capacitor is high enough:

    - for closing and opening if the CB is open or

    - for opening if it is closed

    Output 5 is the inverse of output 4. This logical combination gives the customer a clear indication of the functional

    ability of the breaker. Additionally, the READY-signal is

    monitored via a LED at the front panel of the circuitbreaker.The NOC ON and OFF signals are designed from electronic relays capable of carrying and switchinga current of

    up to 0.5A at a voltage of up to 400 V DC or 280 V AC.

    This is sufficient for energizing e.g. a multiplication relay.

    The most important functions known from conventional

    circuit-breakers are available. Wiring diagrams can be

    taken over with only minor modifications concerning thenumber of ON and OFF signaling outputs.

    The EMC compliance of the electronic control unit has

    been demonstrated in accordance with IEC 1000-4-x by

    various switching capacity tests and extreme voltage tests.

    Furthermore, extensive endurance tests of the electronic

    control unit inside the circuit-breaker have been performed. Here, no electrical problems occurred.


    some parts with high masses and small leads showed mechanical problems. They occasionallybroke off the board.

    All these parts were identified. After they had been glued

    onto the board, several endurance-tests with 100,000CO

    each have been performed without any problems.

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    The energizing of the coils of the actuator for closing and

    opening operations requires a continuous connection to

    some auxiliary voltage supply. In principle, this is also

    true for the conventional mechanical drive. It needs electrical energy for the tripping and closing coils.However,

    this energy amounts to only 1/10th of that necessary for

    the actuator. Because of this reason the actuator coils cannot be directly connected with the controlvoltage, but only

    via a storage device. Batteries or capacitors are very common for this purpose. Capacitors have theadvantage of

    longer lifetime and do not need maintenance in contrast to

    batteries. Even at a relatively high environmental temperature of 55C, the lifetime of modernelectrolytic capacitors is over 30 years.

    The power supply of the electronic control unit shall be

    connected directly to the control voltage supply. The circuit-breaker has then the same availability andpriority as

    all other protection devices. In steady-state the whole unit

    consumes a power of 2 W. Only during recharging of the

    capacitor after switching (2 - 10s) and during the first

    energizing of an empty capacitor (8 - 50s), the current may

    increase to a maximum of 2 A limited by the electronics.

    There is no need for another supply as it is necessary for

    the conventional drive to charge the storage spring.

    Therefore the availability of the new breaker has increased.On failure of the auxiliary voltage, the storage capacitor

    ensures that a breaking operation is possible for further 2

    minutes. Thus, short voltage breakdowns are bridged

    without problems. Conventional breakers would deny

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    with its predecessor, the VD4 circuit-breaker. This facilitates direct replacement in panels, takingaccount of

    course of the specific electrical connection conditions

    which result from the removal of the conventional auxiliary switches.

    Figure 2 contains a schematic diagram of the structure of

    the breaker and a section through the embedded pole part.

    With the embedding in cast resin, which in first place

    upgrades the external dielectric withstand capability of the

    vacuum interrupter and reduces environmental influences

    such as contamination of the surface and condensation, the

    number of detachable components have been kept as lowas possible. This too, significantly reduces the failure potential in relation to assembled pole parts.The mechanical

    strength of the pole parts has been demonstrated in extensive climate and temperature cycle tests (-30 to + 105C).

    Complex electrical and mechanical tests have been performed to demonstrate resistance to aging inoperation.

    The circuit-breaker meanwhile is available with three

    different actuators and two pole part variants for the following performance data, which have beendemonstrated

    to IEC 694 and 56:

    rated voltage rated current breaking current

    12 kV 630 / 1250 A 20 - 25 - 31.5 kA

    17.5 kV 630 / 1250 A 16 - 20 - 25 kA

    24 kV 630 / 1250 A 16 - 20 - 25 kA

    The different short-circuit ratings are achieved with different sizes of actuators coping with therespective peak

    making currents and contact forces. Circuit-breakers with

    higher rated currents of up to 2500 A have been launched



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    The circuit-breaker of type VM1 represents a remarkable

    leap forward in quality. With the permanent magnet actuator and without sensitive latching and controlcomponents, the operator now has a maintenance-free switching

    device. Further breakers with higher rated data will extend

    the range in the near future, making an entire family of

    magnet-operated breakers available. With the use of pole

    parts embedded in cast resin, the way forward has been

    prepared for even more compact circuit-breakers for use in

    switchgear installations of minimum dimensions.

    These maintenance-free components in conjunction with

    the integrated intelligence for control and diagnosis, andin future also for measurement and protection, ensure

    reliable, continuous operation. Favorable experience with

    the new VM1 circuit-breaker in service has already been

    gained. The technical solution presented here shows that

    even with a highly developed switching device like the

    vacuum circuit-breaker, the symbiosis of the familiar vacuum switching technology with a new

    magnetic operatingsystem represents a further optimization of customer



    [1] M. Minovic, Schaltgerte - Theorie und Praxis,

    Htlig und Pflaum Verlag Mnchen, Heidelberg,


    [2] H. Brungsberg, "ber die Verwendung von polarisierten Magnetsystemen fr grereSchaltgerte",

    ETZ vol. 86, 1965, pp.371-375

    [3] B. Mckean; D. Kenworthy, "Bistable magnetic actuator". World patent WO 95/07542, 1994

    [4] B.A.R. Mckean, C. Reuber, "Magnets & Vacuum -

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    the per f ec t ma tch" in Proceed ings

    IEE rends

    in Dis tr ibu tion Switchgear , L ondon , pp. -79


    ] E. Du llni; H . - ink ; . H rner ; . L eonhard t; Chr .

    Reuber , "To ta lly ma in tenance- f ree : new vacuum circu it-breaker with permanen t magne t ac tua tor" ,

    Elek tr i i tsw ir tscha ft, 997 , no , pp .



    ] E. Du llni: " A vacuum circu it-breaker with permanen t magne tic ac tua tor f or f requen t opera tions" , in

    Proceed ings 1998 ISDEIV XVIII, Eindhoven , pp .

    C ircu it B reaker ;

    A c ircu it reaker is an auto m at ically -operated electr ical sw itc h des ig ned to protect an electr ical c ircu it fro m da m a g e caused yo verload or s h ort c ircu it. Its as ic funct ion is to detect a fault cond it ion and, yinterrupt in g cont inu ity, to imm ed iately d iscont inue electr ical flow. Unl ikea fuse, whi c h operates once and th en h as to e replaced, a c ircu it

    reaker can e reset (e ither m anually or auto m at ically ) to resu m e nor m al operat ion. C ircu it reakers are m ade in vary in g s iz es, fro m s m all

    de vices th at protect an ind ivi dual h ouse h oldappl iance up to lar g esw itc hg ear des ig ned to protect high v olta g e c ircu its feed in g an ent irec ity. Or igi n :

    An early for m of c ircu it

    reaker was descr i


    yEd ison in an 1879patent appl icat ion, alt h ou gh hi s co mm erc ial power d istr i ut ion syste m

    used fuses. Its purpose was to protect ligh tin g c ircu it wir in g fro m

    acc idental s h ort -c ircu its and o verloads. Operat in g P r inc iple

    Th e pr im ary funct ion of th e c ircu it reakers m ec h an is m i s to pro vide th e m eans for open in g

    and clos in g th e contacts. In itially, thi ssee m s to e arat h er s im ple and stra igh tforward

    requ ire m ent. Howe ver, wh en onecons iders th e fact th at m ost c ircu it reakers, once placed

    into ser vice,w ill re m a in in th e closed pos ition for lon g per iods of tim e, and yet on th efew

    occas ions wh en th ey arecalled upon to open or close, th ey m ust doso rel iably, w ith out any

    delay or slu ggi s h ness, th en one real iz es th at th ede m ands on th e m ec h an is m s are not as

    s im ple as was f irst th ou gh t. A c ircu it breaker essent ially cons ists of f ixed and m o vin g contacts.

    Th ese contactsare called electrodes. Th e need for carry in g th econt inuous current and for w ith stand in g a per iod of arc in g m akes it

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    necessary to use two sets of contacts in para lle l, one is t h eprimary

    contact and t h e second is t h e arcin contact . Th e primary contact isa lways made of a h i h conducti e materia l suc h as copper and t h e

    arcin contact is made of arcresistance materia l suc h as tun sten or mo lybdenum , wh ic h h as a muc h lowerconducti ity t h an t h ose used for

    primary contacts . Wh

    en th

    e circuit breaker opens to interrupt th

    ecurrent , th e primary contacts open before t h e arcin contacts .

    nder t h e norma l operatin conditions , th ese contacts remain c losedand are not open

    automatica lly unti l and un less t h e system becomesfau lty . f course , th e contacts can be

    opened manua lly or by remotecontro l w h en e er desired . Wh en a fau lt occurs onany part of

    th esystem , th e trip coi ls of t h e circuit breaker et ener i ed and t h e mo in contacts are

    pu lled apart by some mec h anism , th us openin th e circuit .


    en th

    e contacts of a circuit break are separated under fau ltconditions , an arc is struckbetween t h em . Th e current is t h us ab le tocontinue unti l th e disc h ar e ceases .Th e production

    of t h e arc not on lyde lays t h e current interruption process but ita lso enerates enormous h eat

    w h ic h may cause dama e to t h e system or to t h e circuit breakeritse lf . Th erefore , th e main

    prob lem in t h e circuit breaker is to extin uis h th e arc wit h in t h e s h ortest possib le time so t h at

    h eat enerated by itmay not reac h a dan erous a lue .

    In sin le p h ase p h ase) circuits i.e ., li h tin circuits etc .), a switc h is located in on ly one of

    th e two conductors to t h e load . Howe er in t h epower circuits , a circuit interruptin de ice i.e .,

    circuit breaker) is put ineac h p h ase or conductor . Th ese are , sometimes , ca lled 3 po le

    circuitbreakers .

    rc P h enomenon

    rc in an ac circuit breaker occurs in two ways .Wh en t h e current carryin contacts are bein separated , arcin ispossib le e en w h en t h e circuit e .m .f . is considerab ly be low t h e minimum

    co ld e lectrode breakdown o lta e , because of t h e ions neutra li in th e

    e lectronic space c h ar e and t h us a llowin lar e currents to f low atre lati e ly low o lta e radients . Th is way of occurrence of an arc iscommon to bot h dc and ac circuit breakers .

    2 .Th e ot h er way of occurrence of an arc h appens on ly in ac circuitbreakers . In suc h case , th e arc is extin uis h ede ery time t h e current

    passes t h rou h ero and can restrike on ly if t h e transient reco ery o lta e across t h e e lectrodes a lready separated and continuin toseparate , reac h es a sufficient ly h i h a lue causin breakdown .Th e

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    funct ion of an ac c ircu it breaker is to pre vent restr ikin g of th e arc, whi c h

    depends upon th e follow in g im portant factors :

    Th e nature and pressure of th e m ed iu m of arc.

    Th e external ion izi n g and de -ion izi n g a g ents present.

    Th e volta g e across th e electrodes and its var iat ion w ith tim e.

    Th e m ater ial and conf ig urat ion of th e electrodes.

    Th e nature and conf ig urat ion of th e arc in g c h a m ber.

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    funct ion of an ac c ircu it breaker is to pre vent restr ikin g of th e arc, whi c h

    depends upon th e follow in g im portant factors :

    Th e nature and pressure of th e m ed iu m of arc.

    Th e external ion izi n g and de -ion izi n g a g ents present.

    Th e volta g e across th e electrodes and its var iat ion w ith tim e.

    Th e m ater ial and conf ig urat ion of th e electrodes.

    Th e nature and conf ig urat ion of th e arc in g c h a m ber. C lass if icat ion of C ircu it Breakers :Based on volta g e :y L ow volta g e y Med iu m v olta g e y High / Extra volta g e y Ultra volta g e Based on locat ion :y Indoor y Outdoor

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    Based on external des ig n :y Dead tank y L ive tank Based on interrupt in g m ed ia :y

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    A ir reakyA ir lasty

    il yS

    yVacuumHowe er , th e most enera l way of c lassification is on t h e basis of medium used for t h e arc extinction , so we wi ll ta lk about t h is type

    3. Th e S g as h as been identified as a g reen h ouse g as , and safetyre g u lations are bein g introduced in many countries in orde r to

    pre ent its re lease into t h e atmosp h ere . Vacuum circuit breaker

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