Er. rahul sharma circuit breaker

PRESENTATION PRESENTATION PRESENTATION PRESENTATION

ONONONON

CIRCUIT CIRCUIT CIRCUIT CIRCUIT

April 23, 2012EE DEPARMENT SEMINAR

CIRCUIT CIRCUIT CIRCUIT CIRCUIT

BREAKERBREAKERBREAKERBREAKER

By: By: By: By: ErErErEr. . . . RahulRahulRahulRahul SharmaSharmaSharmaSharma

Circuit Breaker Classification :Circuit Breaker Classification :Circuit Breaker Classification :Circuit Breaker Classification :----

On basis of type of Current: 1. AC Circuit Breaker

2. DC Circuit Breaker

On basis of type of Rated Voltage: 1. Low Voltage Circuit Breaker (<1KV)

2. High Voltage Circuit Breaker (>1KV)

On basis of type of Medium Of Arc Extinction :

Air Break Oil CBMCB Minimum Air Blast Vacuum SF6 CBAir Break

CB

Oil CBMCB Minimum

Oil CB

Air Blast

CB

Vacuum

CBSF6 CB

Plain

Break

Self

Compensated

explosion pot

Impulse

Arc

Chute

Magnetic

Blow Out

Cross

Blast

Plain

Break

Self

Blast

Plain

Explosion

pot

X-jet

explosion

Pot

Axial

Blast

Radial

Blast

Plain Break Oil Circuit BreakerPlain Break Oil Circuit BreakerPlain Break Oil Circuit BreakerPlain Break Oil Circuit Breaker

•There is no special arc control system other

than increasing length caused by

separation of contacts.

•It consists of fixed and moving contacts enclosed

in a strong weather-tight earthed tank containing

oil up to a certain level and an air cushion above

the oil level.

•The air cushion collects arc gases without

•When fault occurs, the moving contacts are pulled

down by protective system and an arc is struck

which vaporizes the oil mainly into hydrogen gas.

•The air cushion collects arc gases without

generation of unsafe pressure in the dome of

circuit breaker.

• It also absorbs mechanical shock of the

upward oil movement.

Oil CB Types

As the arc lengthens due to the separating contacts, the dielectric strength of the

medium is increased.

Disadvantages: There is no special control over the arc other than increase in

length by, separating the moving contacts.

Thus capacity installations for low voltages not exceeding 11 kV

Plain Break Oil Circuit Breaker Contd.

The following processes facilitate the arc extinction:

The hydrogen bubble generated around the arc cools the arc and aids deionistion

of the medium between the contacts.

The gas sets up turbulence in the oil and helps in eliminating the arcing products

from the arc path.

Thus capacity installations for low voltages not exceeding 11 kV

Oil CB Types

If some arc control is incorporated and the breakers are then called arc control

circuit breakers.

There are two types of such breakers:

1. Self-blast oil circuit breakers – in which arc control is provided by internal means

i.e. arc itself facilitates its own extinction efficiently.

2. Forced blast oil circuit breakers – in which arc control is provided by mechanical

means external to the circuit breaker.

SelfSelfSelfSelf----Blast Blast Blast Blast OOOOil il il il CCCCircuit Breakers ircuit Breakers ircuit Breakers ircuit Breakers

In this type of breakers, the gases produced during arching are confined to a small

volume by the use of an insulating rigid pressure chamber or explosion pot surrounding

the contacts.

The space available for the arc gases is restricted by the chamber so a very high pressure

is developed to force the oil and gas through or around the arc to extinguish it.

The magnitude of the pressure depends upon the value of fault current to be interrupted.

Oil CB Types

The pressure chamber is relatively cheap and gives reduced final arc extinction gap

length and arcing time as against the plain oil breaker.

The magnitude of the pressure depends upon the value of fault current to be interrupted.

The arc itself generates the pressure so such breakers are also called self-generated

pressure oil circuit breakers.

•It is a rigid cylinder of insulating material and encloses the

fixed and moving contacts.

•The moving contact is a cylindrical rod passing through a

restricted opening called throat at the bottom.

•When fault occurs the contacts get separated and an arc is

struck between them.

•The heat of the arc decomposes oil into a gas at very high

pressure in the pot.

•This high pressure forces the oil and gas through and

around the arc to extinguish it.

Plain Explosion Pot Plain Explosion Pot Plain Explosion Pot Plain Explosion Pot Self-Blast Oil Circuit Breakers Contd.

around the arc to extinguish it.

•Thus emergence of moving contact will be followed by

violent rush of gas and oil through the throat producing

rapid extinction.

Limitation of this type of pot is that it cannot be used for very low or very high fault

currents.

•With low fault currents, the pressure developed is small, thereby increasing the arcing

time.

•And with high fault currents, the gas is produced so rapidly that the plot may burst due

to high pressure. So this pot is used on moderate short circuit currents only where rate of

gas evolution is moderate.Oil CB Types

Cross Cross Cross Cross JJJJet et et et EEEExplosion xplosion xplosion xplosion PPPPot ot ot ot

•The cross jet pot which is made of insulating material and has channels on one side that

acts as arc splitters.

•The arc splitters help in increasing the arc length,

thus facilitating arc extinction.

•When fault occurs, the moving contacts of the

circuit breaker begins to separate and arc is struck in

the top of the pot.

•The gas generated by the arc exerts pressure on the

oil in the back passage.

Self-Blast Oil Circuit Breakers Contd.

•When the moving contact uncovers the arc splitter

ducts, fresh oil is forced across the arc path.

•The cross jet explosion pot is used for interrupting heavy fault currents.

•For low fault currents the gas pressure is small and consequently the pot does not give a

satisfactory operation.

oil in the back passage.

•The arc is therefore driven sideways into the arc

splitters, which increase the arc length, causing arc

extinction.

Oil CB Types

• This pot is a combination of plain explosion

pot and cross jet explosion pot.

•So it can interrupt low as well as heavy short

circuit currents.

Self Self Self Self CCCCompensated ompensated ompensated ompensated EEEExplosion Pot xplosion Pot xplosion Pot xplosion Pot Self-Blast Oil Circuit Breakers Contd.

Oil CB Types

•In this type of circuit breaker there is a piston attached to a moving contact.

•When fault occurs the moving contact moves and hence the piston associated

with it also moves producing pressure inside the oil chamber.

•So the oil gets movement or turbulates and quenches the arc.

Forced Blast Oil Circuit BreakerForced Blast Oil Circuit BreakerForced Blast Oil Circuit BreakerForced Blast Oil Circuit Breaker

Minimum Oil Circuit Breaker Minimum Oil Circuit Breaker Minimum Oil Circuit Breaker Minimum Oil Circuit Breaker

Minimum Oil CB

Minimum Oil Circuit Breaker Contd.

ConstructionConstructionConstructionConstruction

•There are two chambers.

•The oil in each chamber is separated from each other.

•The main advantage of this is that low oil is required and oil in second chamber

wont get polluted.

•Upper chamber is called the circuit breaker chamber and lower one is called the

supporting chamber.

•Vents are placed in a turbulator.

•Circuit breaking chamber consists of moving contact and fixed contact.

•Moving contact is connected with a piston its just for the movement of the contact

and no pressure build due to its motion.

•There are two vents on fixed contact they are axial vent for small current produced in oil

due to heating of arc and radial vents for large currents.

•The whole device is covered using Bakelite paper and porcelain for protection.

Minimum Oil CB

OperationOperationOperationOperation


•Under normal operating conditions, the moving contacts remain engaged with the

upper fixed contact.

•When a fault occurs, the moving contact is pulled down by the tripping springs and an

arc is struck.

•The arc vaporizes oil and produces gases under high pressure.

•The process of turbulation is orderly one, in which the sections of arc are successively

quenched by the effect of separate streams of oil ,moving across each section in turn

and bearing away its gases.

Minimum Oil CB

•This action constrains the oil to pass through a central hole in the moving contact and

results in forcing series of oil through the respective passages of the turbulator.

•Maintenance problems are reduced

Advantages:Advantages:Advantages:Advantages:----

A low oil circuit breaker has following advantages compared to bulk oil circuit breaker

•It requires lesser quantity of oil

•It requires smaller space

•There is reduced risk of fire


Disadvantages:Disadvantages:Disadvantages:Disadvantages:----

A low oil circuit breaker has following disadvantages compared to bulk oil circuit breaker

•Due to smaller quantity of oil, the degree of carbonization is increased

•There is a difficulty of removing the gases from the contact space in time

•The dielectric strength of oil deteriorates rapidly due to high degree of carbonization.

Minimum Oil CB

Vacuum Circuit Breaker Vacuum Circuit Breaker Vacuum Circuit Breaker Vacuum Circuit Breaker

Vacuum Circuit Breaker

Vacuum Circuit Breaker Contd.

•When contacts of a breaker are opened in

•Vacuum is being used as the arc quenching

medium.

•Vacuum offers highest insulating strength.


•When contacts of a breaker are opened in

vacuum, the interruption occurs at first

current zero with dielectric strength

between the contacts building up at a rate

thousands of times that obtained with

other circuit breakers.

•As soon as the arc is produced in vacuum, it is quickly extinguished due to the fast

rate of recovery of dielectric strength in vacuum.

Principle: Principle: Principle: Principle: Vacuum Circuit Breaker Contd.

•When the contacts of the breaker are opened in vacuum (10 -7 to 10 -5 torr), an arc is

produced between the contacts by the ionization of metal vapours of contacts.

•The arc is quickly extinguished because the metallic vapours, electrons, and ions

produced during arc condense quickly on the surfaces of the circuit breaker contacts,

resulting in quick recovery of dielectric strength.

Construction:Construction:Construction:Construction:


•The arc shield prevents the deterioration of the internal dielectric strength by

preventing metallic vapours falling on the inside surface of the outer insulating cover.

Construction:Construction:Construction:Construction:• It consists of fixed contact, moving contact and arc shield mounted inside a vacuum

chamber.

•The movable member is connected to the control mechanism by stainless steel bellows .

•This enables the permanent sealing of the vacuum chamber so as to eliminate the

possibility of leak .

•A glass vessel or ceramic vessel is used as the outer insulating body.


•Since vacuum has very fast rate of recovery of dielectric strength, the arc extinction

Working: Working: Working: Working:

•When the breaker operates the moving contacts separates from the fixed contacts and

an arc is struck between the contacts.

•The production of arc is due to the ionization of metal ions and depends very much

upon the material of contacts.

•The arc is quickly extinguished because the metallic vapours, electrons and ions

produced during arc are diffused in short time and seized by the surfaces of moving

and fixed members and shields.


•Since vacuum has very fast rate of recovery of dielectric strength, the arc extinction

in a vacuum breaker occurs with a short contact separation.

•For outdoor applications ranging from 22 kV to 66 kV. Suitable for majority of

applications in rural area.

Applications: Applications: Applications: Applications:


AdvantagesAdvantagesAdvantagesAdvantages::::

a. They are compact, reliable and have longer life.

b. There are no fire hazards

c. There is no generation of gas during and after operation

d. They can interrupt any fault current. The outstanding feature of a VCB is that

it can break any heavy fault current perfectly just before the contacts reach

the definite open position.


e. They require little maintenance and are quiet in operation

f. Can withstand lightning surges

g. Low arc energy

h. Low inertia and hence require smaller power for control mechanism.

Air Blast Circuit BreakerAir Blast Circuit BreakerAir Blast Circuit BreakerAir Blast Circuit Breaker

•Fast operations •Suitability for repeated operation •Auto Reclosure

•Unit type multi break constructions •simple assembly

•Air blast circuit breakers is used for interconnected lines and important lines

where rapid operation is desired.

•High pressure air at a pressure between 20 to 30 kg/ cm2 stored in the air reservoir.

Air is taken from the compressed air system.

•Three hollow insulator columns are mounted on the reservoir with valves at their

basis.

Air blast circuit breaker

•Since there exists a very high voltage between the conductor and the air reservoir,

the entire arc extinction chambers assembly is mounted on insulators.

basis.

•The double arc extinguished chambers are mounted on the top of the hollow

insulator chambers.

•The current carrying parts connect the three arc extinction chambers to each other

in series and the pole to the neighboring equipment.

Air blast circuit breaker Contd.



•There are three double arc extinction poles in series, there are six breaks per pole.

•Each arc extinction chamber consists of one twin fixed contact.

•There are two moving contacts. The moving can move axially so as to open or close.

•Its position open or close depends on air pressure and spring pressure.

•The operating mechanism operates the rod when it gets a pneumatic or electrical

signal. The valves open so as to send the high pressure air in the hollow of the

insulator. The high pressure air rapidly enters the double arc extinction chamber.

•As the air enters into the arc extinction the pressure on the moving contacts


•However, during the arcing period the air goes out through the openings and take

away the ionized air of the arc.

•As the air enters into the arc extinction the pressure on the moving contacts

becomes more than spring pressure and contacts open.

•The contacts travel through a short distance against the spring pressure.

•At the end of the contact travel the port for outgoing air is closed by the

moving and the entire arc extinction chamber is filled with high pressure air as

the air is not allowed to go out.


•While closing, the valve is turned so as to close connection between the hollow

of the insulator the reservoir.

•The valve lets the air from the hollow insulator to the atmosphere.

•As a result of the pressure of air in the arc extinction chamber is dropped down

to the atmospheric pressure and the moving contacts close over the fixed

contacts by virtue of the spring pressure.

•The opening is fast because the air takes a negligible time to travel from the


•Closing is also fast because the pressure in the arc extinction chamber drops

immediately as the valve operates and the contacts close by virtue of the spring

pressure.

•The opening is fast because the air takes a negligible time to travel from the

reservoir to the moving contact.

•The arc is extinguished within a cycle.

•Therefore, air blast circuit breaker is very fast in breaking the current.


Principle of Arc quenching in Air Blast Circuit Breaker (ABCB)Principle of Arc quenching in Air Blast Circuit Breaker (ABCB)Principle of Arc quenching in Air Blast Circuit Breaker (ABCB)Principle of Arc quenching in Air Blast Circuit Breaker (ABCB)

•It needs an auxiliary compressed air system which supplies air to the air receiver of

the breaker.

•For opening operation, the air is admitted in the arc extinction chamber. It pushes

away the moving contacts.

•In doing so, the contacts are separated and the air blast takes away the ionized gases


•Hence a small contact gap of few centimeters is enough.

•In doing so, the contacts are separated and the air blast takes away the ionized gases

along with it and assists in extinction.

•After a few cycles the arc is extinguished by the air blast and the arc extinction

chamber is filled with high pressure air (30 kg/cm2).

•The high pressure air has higher dielectric strength than that of atmospheric pressure.


•The air flows from high pressure reservoir to the atmospheric through a convergent

divergent nozzle.

•The difference is pressure and the design of the nozzle is such that the air expands

into the low pressure zone, it attains almost supersonic velocity.

Axial Blast type air flowAxial Blast type air flowAxial Blast type air flowAxial Blast type air flow



•The mass flow of air through the nozzle is governed by the parameters like pressure

ratio, area of throat, nozzle throat diameter and is influenced by the diameter of the arc

itself.

Axial Blast Contd.

•The air flowing at a high speed axially along the arc causes the removal of heat from

the periphery of the arc and the diameter of the arc reduces to a low value at current

zero.


•The flow of fresh air through the contact space ensures removal of hot gases and rapid

building up of dielectric strength.

•At this instant the arc is interrupted and the contact space is flushed with fresh air

flowing through the nozzle.


Cross Blast flow Cross Blast flow Cross Blast flow Cross Blast flow

•The air flows around the arc and the diameter of arc is likely to remain stable for higher

values of current.

•During the period of arc extinction, the air continues to flow through the nozzle to the

atmosphere.

•The mass flow rate can be increased by

increasing the pressure of high pressure


•The energy supplied for arc extinction

is obtained from high pressure air and

is independent of current to be

interrupted.

increasing the pressure of high pressure

system.

•The increase in the mass flow results in

the increased breaking capacity.


Sequence of Operation In ABCBSequence of Operation In ABCBSequence of Operation In ABCBSequence of Operation In ABCB

After the brief duration of air flow, the interrupter is filled with high pressure air. The

dielectric strength of air increases with pressure. Hence the fresh high pressure air in

the contact space is capable of withstanding the transient recovery voltage.


Resistance SwitchingResistance SwitchingResistance SwitchingResistance Switching


•The post zero resistance of

contact space is high in air blast

circuit breakers.

•This is because the contact

clearance space is filled with

high pressure air after final


•The high restriking voltage

appears across the contacts does

not damp out through the gap

because of the high post zero

resistance.

high pressure air after final

current zero and high pressure

air has high dielectric strength.

Opening operationOpening operationOpening operationOpening operationAir blast circuit breaker Contd.

•Air is admitted in the arc extinguishing chamber. It separates the main contacts and

pushes the auxiliary contacts.

•The auxiliary contacts close, thereby the resistors are connected across the arc for a

short time of arcing.

•The auxiliary contacts are located in the inclined V shaped insulators while the

resistors are located in the vertical insulators.

•Immediately after the arc extinction the pressure on either side of the piston of

auxiliary contacts gets so adjusted that the auxiliary contacts open and resistor

circuit is interrupted.

•Thus the main arc current is partly diverted through resistor unit. As current

reduces, the resistance offered by non linear resistors increases causing a greater

drop across the resistor units.


circuit is interrupted.

•Ceramic resistances of non linear characteristics, similar to those used in the

lightning arresters are used for resistance switching.

•These consist of silicone carbide, bound by inorganic binders subjected to heat

treatment. During high current, non liner resistor offers low resistance.

•Thereby the voltage available for arc between auxiliary contacts is no more

sufficient and arc between auxiliary contacts is automatically extinguished.

Depending upon the direction of air blast in relation to the arc;air blast circuit

breakers are classified into:



((((iiii)Axial)Axial)Axial)Axial----blast type blast type blast type blast type in which air-blast is

directed along the

arc path

(ii) Cross(ii) Cross(ii) Cross(ii) Cross----blast type blast type blast type blast type in which air blast is

directed at right angles

to the arc path

(iii) Radial(iii) Radial(iii) Radial(iii) Radial----blast type blast type blast type blast type in which the air blast is

directed radially


(i)(i)(i)(i) AxialAxialAxialAxial----blast air circuit breakerblast air circuit breakerblast air circuit breakerblast air circuit breaker

•The fixed and moving contacts are

held in closed position by spring

pressure under normal conditions.

•The air reservoir is connected to

the arcing chamber through an air

valve.


•This valve remains closed under

normal conditions but opens

automatically by tripping impulse

when a fault occurs on the system.


Axial-blast Contd.

•The high pressure air entering the arcing chamber pushes away the moving contact

against spring pressure.

•The moving contact is separated and an arc is struck.

•At the same time,high pressure air blast flows along the arc and takes away the

ionised gases along with it.

•Consequently,the arc is extinguished and current flow is interrupted. ,the

contact separation required for interruption is generally small about 1.75 cm.


•This switch opens immediately after fault interruption to provide necessary

clearance for insulation.

contact separation required for interruption is generally small about 1.75 cm.

•Such a small gap may constitute inadequate clearance for the normal service

voltage.

•Therefore,an isolating switch is incorporated as part of this type of circuit

breaker.


(ii) Cross Blast air breaker(ii) Cross Blast air breaker(ii) Cross Blast air breaker(ii) Cross Blast air breaker

•The cross-blast lengthens and forces

the arc into a suitable chute for arc

extinction.

•When the moving contact is

withdrawn, an arc is struck between

the fixed and moving contacts.

•The high pressure cross-blast forces

into a chute consisting of an arc splitters


•Since the blast pressure is same for all currents, the inefficiency at low currents is

eliminated.

into a chute consisting of an arc splitters

and baffles.

•The splitters serve to increase the

length of the arc and baffles give

improved cooling.

•The result is that arc is extinguished and flow of current is interrupted.

SF6 Circuit BreakerSF6 Circuit BreakerSF6 Circuit BreakerSF6 Circuit Breaker

Working: Working: Working: Working:

•In the closed position of the breaker the contacts remained surrounded by

SF6 gas at a pressure of about 2.8 kg/cm2.

•When the breaker operates the moving contact is pulled apart and an arc

is struck between the contacts.

•The movement of the moving contact is synchronized with the opening of

a valve which permits SF6 gas at 14 kg/cm2 pressure from the reservoir to

SF6 Circuit Breaker

•After the breaker operation the valve is closed by the action of a set of springs.

a valve which permits SF6 gas at 14 kg/cm2 pressure from the reservoir to

the arc interruption chamber.

•The high pressure flow of SF6 rapidly absorbs the free electrons in the arc

path to form immobile negative ions which are ineffective as charge a

carriers.

•The result is that the medium between the contacts quickly builds up high

dielectric strength and causes the extinction of the arc.

•When the contacts separate, an arc is established.

•If the current is not very high, it is extinguished at its first zero crossing by deionizing

effects of SF6, and by the pushing the SF6 through the arc by the piston.

•The contact distance at this point is small and the pressure of the gas that goes through

the arc is low.

•This feature is important because it prevents current chopping when interrupting small

inductive currents.

•In the case of small capacitive currents, the maximum recovery voltage appears ½

cycle after the arc extinction.

SF6 Circuit Breaker Contd.

•If the short circuit current is high, the arc extinction may not occur at the first zero

crossing, but the gas pressure will increase sufficiently to blow the arc out.

cycle after the arc extinction.

•This give the contacts sufficient time to reach a separation that will be able to

withstand the voltage.

SF6 Circuit Breaker


SF6 Circuit Breaker


Advantages over oil and air circuit breakers:Advantages over oil and air circuit breakers:Advantages over oil and air circuit breakers:Advantages over oil and air circuit breakers:a. Due to superior arc quenching property of SF6 , such breakers have very short

arcing timeb. Dielectric strength of SF6 gas is 2 to 3 times that of air, such breakers can interrupt

much larger currents.

c. Gives noiseless operation due to its closed gas circuit

d. Closed gas enclosure keeps the interior dry so that there is no moisture problem

e. There is no risk of fire as SF6 is non inflammable

f. There are no carbon deposits

g. Low maintenance cost, light foundation requirements and minimum auxiliary

equipment

SF6 Circuit Breaker

equipment

SF6 breakers are totally enclosed and sealed from atmosphere, they are particularly suitable

where explosion hazard exists

Disadvantages:Disadvantages:Disadvantages:Disadvantages:A. SF6 breakers are costly due to high cost of SF6

B. SF6 gas has to be reconditioned after every operation of the breaker, additional

equipment is required for this purpose

SF6 breakers have been used for voltages 115kV to 230 kV, power ratings 10

MVA to 20 MVA and interrupting time less than 3 cycles.

Applications: Applications: Applications: Applications:

•The equipment consists of a compressor, a storage container, a blast valve that


•SF6 is a colorless nontoxic gas, with good thermal conductivity and density

approximately five times that of air.

•SF6 is chemically inert up to temperature of 150 C and will not react with metals,

plastics, and other materials commonly used in the construction of high voltage

circuit breakers.

•The principle of operation is similar to the air blast breakers, except that the SF6

gas is not discharged into the atmosphere.

•The equipment consists of a compressor, a storage container, a blast valve that

admits gas to the interrupting chamber, and a filter through which the exhaust gas

is returned to the compressor. This is called the double pressure breaker design.

SF6 Circuit Breaker

AirAirAirAir BreakBreakBreakBreak CCCCircuitircuitircuitircuit BBBBreakerreakerreakerreaker

•These circuit breakers employ high resistance interruption principle.

•The arc is rapidly lengthened by means of the arc runners and arc chutes and the

resistance of the arc is increased by cooling, lengthening and spilitting the arc.

•The arc resistance increases to such an extent that the voltage drop across the arc

becomes more than the supply voltage and the arc extinguished.

•Air breaker circuit breakers are used in d.c circuits and a.c circuits upto 12 kV.

Air Break Circuit Breaker

•The arc resistance is increased to such an extent that the system voltage cannot

maintain the arc and the arc gets extinguished.

•Air breaker circuit breakers are used in d.c circuits and a.c circuits upto 12 kV.

•Magnetic field is utilized for lengthening the arc in high voltage air break circuit

breaker.

Air Break Circuit Breaker Contd.



•Main contacts conduct the current in closed position of the breaker. They have low

contact resistance and are silver plated.

•The arching contacts (2) are hard, heat resistance and usually made of copper alloy.

•While opening the contact, the main contacts dislodge first.

•The current is shifted to the arching contacts.

•The arching contacts dislodge later and arc is drawn between them (3).


•This arc is forced upwards by the electromagnetic force and thermal action.

•The arc ends travel along the Arc Runner (Arcing horns).

•The arc moves upwards and is split by arc splitter plates (5).

•The arc is extinguished by lengthening, cooling, splitting etc.

•In some breakers the arc is drawn in the direction of the splitter by magnetic field.

•The solenoid mechanisms drive power from battery supply or rectifiers.

Operating Mechanisms for Air Break Circuit BreakersOperating Mechanisms for Air Break Circuit BreakersOperating Mechanisms for Air Break Circuit BreakersOperating Mechanisms for Air Break Circuit Breakers


The operating mechanisms are generally operating spring. The closing

force is obtained from the following means:

a. Solenoid

b. Spring charged manually or by motor

c. Pneumatic

•The solenoid mechanisms drive power from battery supply or rectifiers.

•The solenoid energized by the direct current gives the necessary force for the closing

of the circuit breaker.

•The springs used for closing operation can be charged either manually or by motor

driven gears.

•At the time of closing operation the energy stored in the spring is released by

unlatching of the spring and is utilized in closing of the circuit breaker.


ARC VOLTAGEARC VOLTAGEARC VOLTAGEARC VOLTAGEThe voltage that appears across the

contacts of circuit breaker during the

arcing period is known as arc voltage. It

tends to maintain the current flow in the

form of arc.

RESTRIKING VOLTAGERESTRIKING VOLTAGERESTRIKING VOLTAGERESTRIKING VOLTAGEIt’s the transient voltage that appear

across the contacts at or near current

zero during arcing Period.

RECOVERY VOLTAGERECOVERY VOLTAGERECOVERY VOLTAGERECOVERY VOLTAGEIt’s the normal frequency voltage (rms) that appear across the contacts of circuit breaker

after final arc extinction. It is approximately equal to the system voltage. When contacts

are opened current drops to zero at every half cycle. At current zero dielectric strength

of the medium can be increased and thus prevent the break down by restriking voltage.

Consequently the final arc extinction takes place and circuit current is interrupted. After

this current interruption the voltage appearing across the contacts is known as recovery

voltage

•It is the phenomenon of circuit interruption

before the natural current zero is reached.

•It mainly occurs in air blast circuit breakers

because they retain the same extinguishing

power irrespective of the magnitude of current

to be interrupted.

•

The powerful deionising effect of air blast

CURRENT CHOPPINGCURRENT CHOPPINGCURRENT CHOPPINGCURRENT CHOPPING

The powerful deionising effect of air blast

causes the current to fall abruptly to zero well

before the natural current zero is reached.

•This phenomenon is known as current

chopping and results in high voltage transient

across the contacts of the circuit breaker.

•The arc current i is chopped down to zero

value as shown by point

Er. rahul sharma circuit breaker

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