Circuit

1. VACUUM MV CIRCUIT
BREAKERS
SECONDARY DISTRIBUTION
VD4/R - VD4/S – VD4/UNIMIX –
VD4/UNIAIR
CIRCUIT BREAKERS

2. SUB – STATION LAYOUT

3. P
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132K
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220K
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220K
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132K
VBUS
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F SS:11-12-1976
7.2M
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C.B
33K
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REFERENCE
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BREAKER
CT
CV
T
LA
ISOLATOR

4.  INTRODUCTION
 TYPES OF CIRCUIT BREAKERS
 CIRCUIT BREAKER RATINGS
 OPERATING MECHANISM
 CONCLUSION
CONTENT

5. INTRODUCTION
 WHAT IS CIRCUIT BREAKER??
 NEED OF CIRCUIT BREAKER??
 WHERE IT IS USED??
 HOW IT OPERATES??

6. WHAT IS CIRCUIT BREAKER??
 A circuit breaker is an
automatically-operated
electrical switch designed
to protect an electrical
circuit from damage
caused by overload or
short circuit
Circuit breaker layout

7. CAUSE FOR ARC FORMATION
Equivalent circuit Arc phenomenon

8. ARC PHENOMENON
 when a short circuit
occurs, the contacts of
circuit breaker begin to
separate
 The p.d between the
contacts is sufficient to
ionize the air or oil or
gas.
 This ionized air acts as
conductor and ARC is
struck between them even
though contacts of
breaker are opened

9. ARC INTERRUPTION METHODS:
 The resistance of arc is
increased by
1.Cooling of arc
2.Increasing the length of
arc
3.Reducing the cross
sectional area of arc
4.Spliting of arc
 If rate of heat generation is
greater than rate of heat
dissipation between the
contacts arc will be
extinguished.
 if the dielectric strength
increases more rapidly than the
restricking voltage arc is
extinguished.

10. TYPES OF CIRCUIT BREAKERS
based of insulating medium employed in the circuit
breakers , CB’s are 4types
 1. Oil Circuit Breakers
 2. Air Blast Circuit Breakers
 3. Vacuum Circuit Breakers
 4. Sulphur Hexafluoride (SF6) Circuit Breakers

11. 1).OIL CIRCUIT BREAKERS

12. OIL CIRCUIT BREAKERS
e
The arc extinction is facilitated mainly
by two processes:
 Firstly, the hydrogen gas has high
heat conductivity and cools the arc,
thus aiding the de-ionization of the
medium between the contacts.
 Secondly, the gas sets up turbulence
in the oil and forces it into the space
between contacts, thus eliminating th
arcing products from the arc path.
 The result is that arc is extinguished
and circuit current interrupted.

13. TYPES OF OIL CIRCUIT
BREAKERS
 which use a large quantity
of oil. The oil has to serve
2 purposes.
 1. it extinguishes the arc
during opening of
contacts and ,
 2. it insulated the current
conducting parts from
one another and from the
earthed tank.
 (a)
 (b)
Plain break oil CB
Arc control oil CB
Bulk oil circuit breakers
Cross sectional view
Of
bulck oil CB

14. TYPES OF OIL CIRCUIT
BREAKERS
Low oil circuit breakers
 which use minimum
amount of oil. In such
circuit breakers, oil is
used only for arc
extinction; the current
conducting parts are
insulated by air or
porcelain or organic
insulating material.

15.  1. It requires smaller
space for installation.
 2. Maintenance
problems are reduced.
 3. Requires less
quantity of oil.
 4. Risk of fire is
reduced.
 1. The degree of
carbonization is increased
due to less quantity of oil.
 2. Difficulty of
removing the gases from
the contact space in time.
 3. Possibility of
explosion.
 4. The dielectric
strength of the oil
deteriorates rapidly due to
high degree of
carbonization.
Advantages: Disadvantages:

16. AIR BLAST CIRCUIT
BREAKERS
2).AIR BLAST CIRCUIT BREAKERS

17. AIR BLAST CIRCUIT BREAKERS
 Compressed air between 20-30
kg/cm^2 is used for arc extinction in
this type of
breakers.
 A compressor is needed for
maintaining the air preserving .
 Arc is blown away by the blast of air
under pressure.
 After the arc extinction the arcing
chamber is filled with compressed
air again to prevent restricting of the
arc.
 The air gap (-1.75cm) is very small
between the contacts after
separation.

18. THERE ARE 3 TYPES OF AIR BLAST CB’S
fig: cross flow ABCB
Axial-blast type Cross-blast type
In this type of breaker the air
blast is directed along the arc
path. The fixed and moving
contacts are held in the
closed position by spring
pressure under normal
condition
In this type of breaker an air
blast is directed at right angles to
the arc.
The cross blast lengthens and
forces the arc into a suitable
chute (Arc splitters) for arc
extinction.

19. 1.The risk of fire is
eliminated.
2.Cheap compared to oil circuit
breaker
3.Arcing time is very less thereby
less burning of contacts
DisAdvantages
1.The air blast circuit breakers are very
sensitive, to the variations in the rate of
rise of restriking voltage
.
2.Maintenance is required for
compressor plant which supplies air
blast.
Advantages
Radial-blast type

20. VACCUM CIRCUIT
3).VACCUM CIRCUIT BREAKERS(VCB)

21. VACCUM CIRCUIT BREAKERS(VCB)
In such breakers, vacuum degree of
vacuum being in the range from (106-
7 torr) is used as the arc quenching
medium.
Since vacuum offers the highest
insulating strength, it has far superior
arc quenching properties than any
other medium.
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.

22.  When the breaker operates, the
moving contact separates from the
fixed contact and an arc is struck
between the contacts.
 The arc is quickly extinguished
because the metallic vapors,
electrons and ions produced during
arc are diffused in a 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 (say 0.0625 cm).

23.  1. VCB are compact,
reliable and have longer
life .
 2. They have low arc
energy.
 3. Risk of fire is
eliminated.
 4. Maintenance is less.
 5. There is no
generation of gas during
and after operation.
 6. They can withstand
lightning surges.
Advantages Disadvantages
 1. Vacuum circuit
breakers are very expensive
.Production in small
quantities is
uneconomical.
 2. For above 36KV VCB
`s are not used.
 3. They require high
technology for production.
 4. In case of loss of
vacuum, the entire breaker
is useless .

24. SULPHUR HEXAFLUORIDE (SF6) CB
OIL CIRCUIT BREAKERS
4).SULPHUR HEXAFLUORIDE (SF6) CB

25. SULPHUR HEXAFLUORIDE (SF6) CB
 SF6 has excellent insulating
strength because of its affinity for
electrons.
 whenever a free electron collides
with the neutral gas molecule to
form negative ion, the electron is
absorbed by the neutral gas
molecule.
 This property of SF6 is
approximately 100 times as effective
as air in quenching arcs.
 SF6 has excellent heat transfer by
convection more effectively than the
common gases.

26.  SF6 consists of 2parts mainly:
 1) The interrupter unit
This consists of fixed contacts which
comprise a set of current carrying
fingers and an arcing probe. As the
contacts move further apart, the arc is
extended and attenuated. It is finally
extinguished by the gas flow the high
pressure to the low pressure systems.
 2) The gas system.
The low and high pressure system are
fitted with low pressure alarms and a
set of lock-out switches which give a
warning the moment the gas pressure
drops below a certain value

27. 1. Due to superior arc
quenching property, SF6
circuit breakers have very
short arcing time.
2. Since the dielectric strength
of SF6 is 2 to 3 times than
that of air , these breakers
can interrupt larger
currents
3. The SF6 circuit breaker
gives noiseless operation
due to its closed gas circuit .
4. Risk of fire is eliminated
because SF6 gas is non-
flammable.
1. SF6 breakers are costly
due to high cost of SF6 .
2. Sealing problems arise ,
Imperfect joints give rise
to leakage of gases.
3. After every operation SF6
gas has to be
reconditioned, so
additional equipment is
required.
Advantages Disadvantages

28. CIRCUIT BREAKER RATINGS
The rating of a circuit breaker is given according to the
duties that are performed by it. The circuit breaker is
required to perform following major duties:
1.A circuit breaker must be capable of breaking the circuit
and isolating the faulty section in case of faults. This is
described as of C.B.
2.It must be capable of being closed under faulty condition.
This is described as of C.B.
3.It must be capable of carrying fault current for a short
period of time.
This is described as .

29. Spring mechanism
For circuit breakers up to 245 KV, spring operating mechanism is used. The
closing spring gets charged by geared motor. During closing stroke the
closing spring is discharged. It closes the breaker and also charges the
opening springs. The C.B mechanism is basically very simple since it
compresses a motor reducer and two springs.
Hydraulic mechanism
The hydraulic cylinder is mounted at the base of interrupter
unit and the hydraulic rod is pushed up during closing stroke and
pushed down during opening stroke.
The hydraulic oil at atmosphere pressure from the low pressure
tank is pumped into accumulators at high pressure oil is used for
opening and closing operations.
OPERATING MECHANISM

30. PNEUMATIC MECHANISM
 The pressure of operating air produced by the self
enclosed motor compressor unit is supervised by a pressure
gauge and controlled by a pressure switch. This type of system
is providing for each pole of 420KV and 765KV.
In EHV OCB, compressed air is used for closing and a
spring is used for opening. The spring is charged during the
closing stroke. In ABCB, compressed air is used for both
closing and opening. In some cases of ABCB, the moving
contact is held in closed position by a spring. When compressed
air enters the arc chamber and its pressure exceeds the spring
force, the contacts are opened. The contacts automatically come
in closed position by the spring action when the supply of
compressed air is stopped. Therefore, the supply of compressed
air must be maintained till the auxiliary CB switch is opened.


31. CONCLUSION
 We have abbendent resources for power generation.
Besides generation we have to protect our transmission
,distridution and household equipment mainly we have
to protect our lifes from electrical hazards. So, for the
protection circuit breaker is a major and important used
device for protecting and intterrupting the power supply
from the fault conditions…

32. I express our heartful thanks to
Mr. RAMU SHRIKAKULAPU
(Asst. Professor)
SHARDA UNIVERSITY
for their encouragement, support, valuable guidance, moral support and
motivations in completing my Presentation.
BY
DINESH SHARMA
BRANCH-EEE(A)
SEMESTER- VIIth
ROLL -100104047
SHARDA UNIVERSITY

33. BY
DINESH SHARMA
BRANCH-EEE(A)
SEMESTER- VIIth
ROLL -100104047
SHARDA UNIVERSITY