Circuit breakers are mechanical switching devices that can make, carry, and break electrical currents under normal and abnormal circuit conditions such as short circuits. They contain two contacts - a fixed contact and a moving contact. The moving contact opens and closes the circuit using stored energy from a spring or compressed air. Circuit breakers also contain closing and tripping coils that activate the stored energy mechanism to open or close the circuit. There are different types of circuit breakers including low, medium, and high voltage varieties as well as air, oil, vacuum, and SF6 models. Proper selection depends on factors like voltage, current rating, frequency, and interrupting capacity.

1. SUBJECT
CIRCUIT BREAKER
PREPARED BY :
Yash kothadia (150110109019)
Abhishek lalkiya (150110109020)
keyur nimavat (150110109027)

2.  Introduction
 Operating mechanism
 Types of circuit breakers
 Basic type of circuit breakers
 Selection of circuit breakers
 Conclusion

3.  A circuit breaker is a mechanical switching
device, capable of making, carrying and breaking
currents under normal circuit conditions. It is also
capable of making and carrying currents for a
specified time and breaking currents under specified
abnormal circuit conditions, such as those of a short
circuit

4.  Circuit Breaker consists of two
contacts:
Fixed contact. Moving contact.
 Moving contact is used to make and
break the circuit using stored energies
in the form of spring or compressed
air.
 Spring, pneumatic or oil damping is
used to arrest the speed of mc while
closing.
 FC contains a spring which holds the
mc after closing.

5.  Circuit breaker consists of two coils:
Closing coil –Used to close the circuit.
Tripping coil-Used to trip the circuit.
 These coils activate the stored energy and
directs the mc to open or close.
 DC batteries are used to energize these coils.
 Solenoids are used to close or trip it.
 CBs are usually arranged with pilot devices to
sense a fault current and to operate the trip
opening mechanism

6.  During the separation of contacts, due to
large fault current and high current density
at the contact region the surrounding
medium ionizes and thus a conducting
medium is formed. This is called the ARC.
 Factors responsible for arc:
 Potential difference between the contacts.
 Ionized particles between the contacts

7.  Arc quenching is achieved by:
 Greater dielectric strength than restriking voltage.
 Faster rate of heat removal than rate of heat
generation.
 Arc extinction methods are:
 By lengthening the gap.
 Cooling the arc. Inserting medium of high dielectric
strength.

8.  Low Voltage Circuit Breakers
 Medium Voltage Circuit Breakers
 High Voltage Circuit Breakers

9.  Air Circuit Breakers
a) Air circuit breaker
b) Air-blast circuit breaker
 Oil Circuit Breakers
a) Minimum oil Circuit Breakers
b) Bulk oil Circuit Breakers
 Vacuum Circuit Breakers
 SF6 Circuit Breakers

10.  There are a few different criteria to consider when
selecting a circuit breaker including
 1. Voltage
 2. Frequency
 3. interrupting capacity
 4. continuous current rating
 5. unusual operating conditions
 6. product testing

11.  Voltage Rating
 The overall voltage rating is calculated by the
highest voltage that can be applied across all
end ports.
 It is important to select a circuit breaker with
enough voltage capacity to meet the end
application.
 Frequency
 Circuit breakers up to 600 amps can be applied
to frequencies of 50120 Hz.
 Higher than 120 Hz frequencies will end up
with the breaker having to derate.

12.  Maximum Interrupting Capacity
 The interrupting rating is generally accepted as
the highest amount of fault current the breaker
can interrupt without causing system failure to
itself.
 Determining the maximum amount of fault
current supplied by a system can be calculated
at any given time.

13.  Continuous Current Rating
 In regards to continuous current rating,
modelled case circuit breakers are rated in
amperes at a specific ambient temperature.
 This ampere rating is the continuous current the
breaker will carry in the ambient temperature
where it was calibrated.
 A general rule of thumb for circuit breaker
manufactures is to calibrate their standard
breakers at 104° F.

14.  Therefore, we conclude that circuit breaker is the
most essential part of the electrical networks as it
protects every device from damage. It helps us to
detect the fault and area affected by it. Nowadays
vacuum and SF6 circuit breakers are widely used
due to their reliable and fast operations.