SF6 gas Circuit Breaker

1. VARENDRA UNIVERSITY
Look at the Future..
Learn from the Past….

2. Welcome To The Presentation
ON
SF6 (Sulphur Hexaflouride) Circuit Breaker

3. Course Title: Switchgear & Protection
Course Code: EEE 413
Presented By :
H. M. Zobdatul Arefin
ID: 171321023
Semester: 10th
Batch: 14th
Dept. of EEE
Presented To :
Tamanna Tasnim
Lecturer
Dept. of EEE
Varendra University

4. Contents:
• Introduction
• History
• Why SF6 gas is used?
• Physical & Chemical properties of SF6 gas
• Types
• Construction
• Operating principle
• Advantages
• Disadvantages
• Application
• Some figure
• Conclusion

5. Introduction:
• A circuit breaker in which the current carrying contacts operate in Sulphur Hexafluoride gas (SF6) is known as SF6 circuit
breaker. It protects electrical power stations and distribution systems by interrupting electric currents, when tripped by a
protective relay.
• SF6 circuit breaker is currently used world-wide. It is estimated that an average of about 80 % of HV equipment
manufactured now has an SF6 content.
 History:
• 1938- First patent on use of SF6 as an interrupting medium were field in Germany by Vitaly Grosse
• 1951-Later in United States by H J Lingal
• 1953-First Industrial Application of SF6 for current interruption with a breaking capacity of 600A
• 1956-First High Voltage circuit breaker built by Westing House, that could interrupt a current of 5kA under 115kV
• 1959- First HV SF6 C.B with high short circuit capability was introduced (up to 41.8kA under 138k)
• 1970-High interrupting capabilities SF6 C.B were developed, up to 800kV
• Presently, SF6 has been adopted for use in ring main units, contactors , bus bar coupler and circuit-breakers, GIS, covering
all the needs of the electrical distribution industry

6. Why SF6 gas is used?
• Due to high electro-negativity
• Sulfur hexafluoride (SF6) is an inert gas with excellent insulating properties
• Exceptional thermal and chemical stability
• It insulates 2.5 times better than air
• Arc quenching capability 100 times better than air
• Better heat dissipation capacity than air
 Physical & Electrical properties of SF6 gas:
• Physical: i) This gas is one of the heaviest gas.
ii) Variation of pressure with temperature is linear and small in range
of service temperature (-25 to +50 degree Celsius)
iii) Volumetric specific heat of it is 3.7 times of air.

7. Physical & Chemical properties of SF6 gas:
• Chemical: i) Chemically inert , ii) Non-toxic, iii) Non-corrosive , iv) Non-flammable , v) Odorless.
 Types:
1. Single interrupter SF6 C.B.(up to 245kv)
2. Two interrupter SF6 C.B.(up to 420kv)
3. Three interrupter SF6 C.B.(up to 800kv)
 Construction:
• The parts of a typical SF6 circuit breaker. It consists of fixed and moving contacts enclosed in a chamber (called arc
interruption chamber) containing SF6 gas. This chamber is connected to SF6 gas reservoir. When the contacts of breaker
are opened, the valve mechanism permits a high pressure SF6 gas from the reservoir to flow towards the arc interruption
chamber. The fixed contact is a hollow cylindrical current carrying contact fitted with an arc horn. The moving contact is
also a hollow cylinder with rectangular holes in the sides to permit the SF6 gas to let out through these holes after flowing
along and across the arc. The tips of fixed contact, moving contact and arcing horn are coated with copper-tungsten arc
resistant material. Since SF6 gas is costly, it is reconditioned and reclaimed by suitable auxiliary system after each
operation of the breaker.

8. Operating principle:
•In the closed position of the breaker, the contacts
remain 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 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 carriers.
• The result is that the medium between the contacts
quickly builds up high dielectric strength and causes the
extinction of the arc.
•After the breaker operation (i.e., after arc extinction),
the valve is closed by the action of a set of springs.

9. Advantages:
• Very short arcing due gas superior arc quenching property
• Noiseless operation dye to it’s closed gas circuit
• No exhaust to atmosphere unlike Air Blast circuit breaker
• No moisture problem
• No risk of fire as SF6 gas is non-inflammable
• Low maintenance cost, light foundation
• Require minimum auxiliary equipment
 Disadvantages:
• Costly due to high cost of gas
• Since SF6 gas has to be reconditioned after every operation of the breaker, additional equipment is required for this
purpose
• Continuous monitoring devices are required
• Arced SF6 gas is poisonous and should not be inhaled
• SF6 gas being heavier than the air settles in the surroundings and may lead to suffocation of the operating personnel
,however it is not poisonous
• It may contribute to the man made greenhouse effect, if it is released into the atmosphere

10. Applications:
• A typical SF6 circuit breaker consists of interrupter units each capable of dealing with currents up-to 60 kA and voltages
in the range of 50—80 kV
• A number of units are connected in series according to the system voltage
• SF6 circuit breakers have been developed for voltages 115 kV to 230 kV
• Power ratings 10 MVA to 20 MVA and interrupting time less than 3 cycles
 Some figure:

11. Conclusion:
• SF6 Circuit breakers are mostly employed for high voltage applications. For protection and reliability of an electrical
substation of an electricity generation, transmission and distribution system where voltage is transformed from high to low
or the reverse using transformers.
• The countless advantages of this SF6 C.B. gas has to offer will take us to new heights in the prevalent power system.
• The adoption of SF6 in switchgear for all operating conditions has brought advantages in performance , size, weight, global
cost and reliability.