Circuit Breaker Classification and Types

PRESENTATION
ON

CIRCUIT
BREAKER
Er.
By: Er. Rahul Sharma
EE DEPARMENT SEMINAR

April 23, 2012

:Circuit Breaker Classification :1. AC Circuit Breaker
2. DC Circuit Breaker

On basis of type of Current:

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
CB

MCB

Oil CB

Minimum
Oil CB

Vacuum
CB

SF6 CB

Air Blast
CB

Plain
Break

Plain
Break

Axial
Blast

Magnetic
Blow Out

Impulse

Radial
Blast

Arc
Chute

Self
Blast

Plain
Explosion
pot

Cross
Blast
X-jet
explosion
Pot

Self
Compensated
explosion pot

Plain Break Oil Circuit Breaker
•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.
•There is no special arc control system other
than increasing length caused by
separation of contacts.
•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.
•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.

Oil CB Types

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.
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
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.
Oil CB Types

SelfSelf-Blast Oil Circuit 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.

The arc itself generates the pressure so such breakers are also called self-generated
pressure oil circuit breakers.
The pressure chamber is relatively cheap and gives reduced final arc extinction gap
length and arcing time as against the plain oil breaker.

Oil CB Types

Plain Explosion Pot

Self-Blast Oil Circuit Breakers Contd.

•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.
•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 Jet Explosion Pot


•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.
•When the moving contact uncovers the arc splitter
ducts, fresh oil is forced across the arc path.
•The arc is therefore driven sideways into the arc
splitters, which increase the arc length, causing arc
extinction.
•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 CB Types


Self Compensated Explosion Pot
• 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.

Forced Blast Oil Circuit Breaker
•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.
Oil CB Types

Minimum Oil Circuit Breaker

Minimum Oil CB

Minimum Oil Circuit Breaker Contd.

Construction
•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.
•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.
•Vents are placed in a turbulator.
Minimum Oil CB


Operation
•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.
•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.
•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


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
•Maintenance problems are reduced

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 Contd.

•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.


Principle:


•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.
•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.

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.
•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.


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.

Applications:
•For outdoor applications ranging from 22 kV to 66 kV. Suitable for majority of
applications in rural area.



Advantages:
Advantages:
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 Breaker
•Fast operations

•Suitability for repeated operation

•Unit type multi break constructions

•Auto Reclosure

•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.
•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.
•Since there exists a very high voltage between the conductor and the air reservoir,
the entire arc extinction chambers assembly is mounted on insulators.

Air blast circuit breaker

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
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.
•However, during the arcing period the air goes out through the openings and take
away the ionized air of the arc.


•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
reservoir to the moving contact.
•The arc is extinguished within a cycle.
•Therefore, air blast circuit breaker is very fast in breaking the current.
•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.


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



Axial Blast type air flow
•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 Contd.

•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.
•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.
•At this instant the arc is interrupted and the contact space is flushed with fresh air
flowing through the nozzle.
•The flow of fresh air through the contact space ensures removal of hot gases and rapid
building up of dielectric strength.



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
system.
•The increase in the mass flow results in
the increased breaking capacity.
•The energy supplied for arc extinction
is obtained from high pressure air and
is independent of current to be
interrupted.


Sequence 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 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
current zero and high pressure
air has high dielectric strength.
•The high restriking voltage
appears across the contacts does
not damp out through the gap
because of the high post zero
resistance.



Opening operation
•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.
•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.
•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.
•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:

(i)Axial-blast type
)Axial-

Cross(ii) Cross-blast type

Radial(iii) Radial-blast type

in which air-blast is
directed along the
arc path

in which air blast is
directed at right angles
to the arc path

in which the air blast is
directed radially



(i) Axial-blast air circuit breaker
Axial•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.
•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.
•This switch opens immediately after fault interruption to provide necessary
clearance for insulation.


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

SF6 Circuit Breaker
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
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.
•After the breaker operation the valve is closed by the action of a set of springs.
SF6 Circuit Breaker

SF6 Circuit Breaker Contd.

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

SF6 Circuit Breaker


SF6 Circuit Breaker

Advantages over oil and air circuit breakers:


a. Due to superior arc quenching property of SF6 , such breakers have very short
arcing time
b. 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 breakers are totally enclosed and sealed from atmosphere, they are particularly suitable
where explosion hazard exists

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

Applications:
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.
SF6 Circuit Breaker


•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

Air Break Circuit Breaker
•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.
•Magnetic field is utilized for lengthening the arc in high voltage 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 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.


Operating 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 VOLTAGE
The 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 VOLTAGE
It’s the transient voltage that appear
across the contacts at or near current
zero during arcing Period.

RECOVERY VOLTAGE
It’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

CURRENT CHOPPING
•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
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

Circuit Breaker Classification and Types

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