Circuit breaker. and its types. fault clearing process, trip circuit, history, technical particulars and operating mechanism of circuit breaker

1. Switchgears and Protective Devices (Sunil S Rao)
Presented By: Engr. FAZAL UR REHMAN
Lecturer Electrical KPTEVTA
Visiting Lecturer COMWAVE INSTITUTE ISLAMABAD

2. Today's Topics
Chapter No. 2
 2.1 Introduction,
 2.2 Fault clearing process (C.B),
 2.3 Trip circuit,
 2.4 Historical Review,
 2.5 Classification Based on Arc Quenching medium,
 2.6 Technical Particulars of a C.B,
 2.9 Operating Mechanism

3. Introduction
 Circuit Breakers are automatic switches which can
interrupt fault current automatically during abnormal
working conditions and used as a simple manual
switch during normal working conditions.
 The current interruption chamber in circuit breaker is
called interrupter.
 Interrupter consist of fixed and moving contacts
mounted on support insulators.
 Circuit breakers can be Single / Two / Triple Pole Type
depending one, two or three phases support ability.

6.  Circuit Breaker:
 Serve two purpose
 Manual Switching during normal conditions for O & M.
 Automatic Switching during abnormal conditions.
 Types on the basis of extinction medium are;
 ACBs
 VCBs
 OCBs etc.

7. Fault clearing process (C.B)
 Automatic switching facility of circuit breaker help
fault clearing process. Which can be achieved by a
circuit known as trip circuit with the help of some
operating mechanism in place.
 And at the end fault is said to be cleared when arc and
fault current level are zeroed.
 This fault clearing process has the following sequence.

8.  Fault Occurs:
 High fault current resulted due to low fault impedance
which activate relay and associated secondary system.
 Relay Contact Closes.
 Relay contact closure will energize the trip circuit for
tripping of circuit breaker.
 Operating Mechanism Start
 Operating mechanism separates the contacts of circuit
breaker by initiating opening process.
 Arc is extinguished.
 Arc is quenched by suitable medium and mechanism.

9. The Trip Circuit
This is an automatic
Circuit for
Tripping of C.B

10. Recent Advances
 Before 1970s
 Air and Oil Circuit Breakers were widely used in
Medium and High Voltage range.
 During 1970s
 Vacuum C.B were introduced for use upto 36 KV system.
 Single pressure puffer type SF6 C.B were introduced
(3.3KV to 760KV)
 SF6 GIS were introduced for 12KV to 760KV.
 Now
 SF6 and Vacuum C.B are preferred due to smooth and
maintenance free operation.

11. History of Circuit Breaker
 In 1956, H. Cross revolutionized the high-frequency-
circuit vacuum switch and produced
a vacuum switch with a rating of 15 kV at 200 A.
 Five years later, Thomas H. Lee at General Electric
produced the first vacuum circuit breakers with a
rated voltage of 15 kV at short-circuit breaking
currents of 12.5 kA.

12. Historical Review

16. Classification of C.B
 On the basis of Arc Quenching medium C.B are
classified as follows;
1. Air Circuit Breaker / MCB
2. Bulk Oil C.B
3. Minimum Oil C.B
4. Air Blast C.B
5. SF6 C.B
6. Vacuum C.B

17.  How Circuit Breaker quench an arc during or after
fault occurrence will be discussed in detail later on.
 Shortly here we can learn that in major there are only
two possible ways for arc quenching;
 High Resistance Method
 Current Zero Method.

18. Technical Particulars of C.B
 Technical particulars mean identifying features of C.B.
 Type of Medium
 Rated Voltage
 Rated Breaking Current
 Type of Construction- indoor(draw out), outdoor, GIS
 Type of Operating Mechanism
 Total Break Time
 Additional Features.

22. Operating Mechanisms
 The operating mechanism creates and stores energy
to operate the circuit breaker.
 The operating mechanism includes the energy storage
medium, actuating circuit and interlocking systems.
 For this operation to occur there is a mechanism working in
background.
 Spring Operated. driven by the mechanical energy stored in
springs.
 Solenoid Operated. driven by the magnetic energy stored in
solenoid.
 Hydraulic Operated. Liquid pressure like hydraulic brakes.
 Pneumatic Operated. Air Pressure.

23.  On the above discussed mechanism there are the
following operating mechanism for C.B
1. Spring Opened Spring Closed Mechanism
2. Solenoid Closed, Spring Opened Mechanism
3. Hydraulic Mechanisms
4. Pneumatic Mechanism.
 These above four types are Stored energy type
Independent Automatic Operating Mechanism.
And are used in all High Voltage Circuit Breakers.

24. Dependent and Independent
Mechanisms
 Dependent operating mechanisms depend on
continuity of power supply or manual forces during
closing. (Dependable manual / Dependable
Power).
 Store energy type Independanble mechanisms are
independent of continuity of power supply or operator
skill. (Independent manual / independent Power)