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.
4.
5.
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.
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.
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.
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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)