PRESENTATION PRESENTATION PRESENTATION PRESENTATION ON ON ON ON CIRCUIT CIRCUIT CIRCUIT CIRCUIT April 23, 2012 EE DEPARMENT SEMINAR CIRCUIT CIRCUIT CIRCUIT CIRCUIT BREAKER BREAKER BREAKER BREAKER By: By: By: By: Er Er Er Er. . . . Rahul Rahul Rahul Rahul Sharma Sharma Sharma Sharma
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•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.
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
Air blast circuit breaker
•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.
Air blast circuit breaker Contd.
•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
Air blast circuit breaker
•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.
Air blast circuit breaker Contd.
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
Air blast circuit breaker
•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.
Air blast circuit breaker Contd.
•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
Air blast circuit breaker
Air blast circuit breaker 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.
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.
Air blast circuit breaker
•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
•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 Contd.
SF6 Circuit Breaker
SF6 Circuit Breaker Contd.
SF6 Circuit Breaker
SF6 Circuit Breaker Contd.
SF6 Circuit Breaker
SF6 Circuit Breaker Contd.
SF6 Circuit Breaker
SF6 Circuit Breaker Contd.
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.
•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.
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).
Air Break Circuit Breaker
•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
Air Break Circuit Breaker Contd.
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.
Air Break Circuit Breaker
Air Break Circuit Breaker Contd.
Air Break Circuit Breaker
Air Break Circuit Breaker Contd.
Air Break 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