ps2 assignment

8/7/2019 ps2 assignment

1/38

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.

Contents

[hide]

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

[edit]Operation

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.


2/38

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

contacts.

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 (


3/38

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 ,


4/38

t

t i t

i i l f t t

t t

i it

t t i it

t i t ti l ti

l i. ., i l t

!

, " i t f I # :

Type I $ % &

'

$

&

'

$ eous &

( ipp i $ g ) urrent

B 0 1 2 3 4 5 I n 6

7 t8 9 nd inc l6 ding @

I n

A 9 B 8 C D @

I n 6

7 t8 9 nd inc l6 ding E F

I n

G 9 B 8 C D E F

I n 6 7 t8 9 nd inc l6 d ing H F

I n

K

9 B 8

C D I I n 6 7 t8 9 nd inc l6 ding E

H

I n

P 8 Q tR

D 7 Q 8 tD cti8 n 8 f l8 9 ds tR

9 t cause f Q equen t shor t dura tion S approx iT a te lU V F F

T s to H

s)

curren t peaks in norma l opera tion .

W

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


5/38

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

Bc

g inia ture h

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

A.i

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

Bc

g olded h

ase h

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

A.i

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

v

h

) 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


6/38

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


7/38

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


8/38

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

gear

kV S live tank circu it breakers


9/38

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

he

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

Vacuum

S

Some of the manu f ac turers are ABB,

E

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 .


10/38

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

lf

r h exa fl

r i de

i rcu it

reaker

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


11/38

Insulation monitoring device

Circuit Total Limitation (CTL)

Network protector

Circuit breaker panel

[edit]References

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. ^ http://bonle.en.alibaba.com/product/50348671/51680889/Switch/MCB___MCCB.html

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

145 kV.

See http://www3.interscience.wiley.com/journal/113307491/abstract?CRETRY=1&SRETRY=0 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.

A VACUUM CIRCUIT-BREAKER WITH PERMANENT MAGNETIC ACTUATOR

AND ELECTRONIC CONTROL

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]

ABSTRACT

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


12/38

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.

INTRODUCTION

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 -


13/38

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


14/38

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.

a)

b)

c)

Figure 3: Distribution of the magnetic field lines

a) in the open position;

b) shortly before the start of the motion;


15/38

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


16/38

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].

ELECTRONIC CONTROL UNIT

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


17/38

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

1

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.


18/38

1

Mean Time Between Failures

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

LOGIC

0,1Farad

6

5

5

1

2

3

4

= 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 (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:


19/38

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

nd

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

available:

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

assured:


20/38

Internal supply voltage is available

The internal control of the FPGA (watchdog) is

positive

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.

However,

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.


21/38

APPLICATIONS OF ELECTRONIC CONTROL

UNIT

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


22/38


23/38

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

recently.

PROSPECTS


24/38

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

benefit.

REFERENCES

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

Htlig und Pflaum Verlag Mnchen, Heidelberg,

1977

[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 -


25/38

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 .

-1212

[

] 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

ed

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


26/38

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 .

Wh

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


27/38


28/38


29/38


30/38

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.


31/38


32/38


33/38


34/38

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


35/38


36/38

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


37/38

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


38/38

Documents

ps2 assignment