Seminar On

“Sf6 circuit breaker”Under The Guidance Of :- Mr. S.S Mohapatra,

Lecturer

CONTENTS• Introduction• SF6 circuit breaker• Why SF6??• Types of SF6 CB• Overview of an arc• Working principle• Principle of arc extinction• Circuit breaker connected with bus bar• Physical and chemical properties• Advantages of SF6 CB• Disadvantages of SF6 CB• Limitation• Conclusion• References

In modern times, high voltages are used for

• Power system• Industry• Research laboratoriesFor safety and protection We use one of the protection device

is SULPHUR HEXAFLUORIDE (SF6 ) gas

circuit breaker. They were first introduced in the

mid 1950s.

A circuit breaker is an equipment which can make or break a circuit either manually or

automatically under normal conditions. break a circuit under abnormal, short circuit ,

overload condition or any other fault. A circuit breaker in which the current carrying

contacts operate in sulphur hexafluoride gas (SF6) is known as SF6 circuit breaker.

SF6 CBs made from 72-800KV with interruption current is 20 to 63KA and rated current of 1200 to 12000A.

WHY SF6 GAS ?

• HIGH ELECTRO-NEGATIVITY

• HIGH DIELECTRIC STRENGTH

• LOW LIQUIFICATION TEMPERATURE

• GOOD ARC QUENCHING

Types of SF6 circuit breaker

1. Single interrupter SF6 CB(upto 245kv)2. Two interrupter SF6 CB(upto 420kv)3. Three interrupter SF6 CB(upto 800kv)

Single interrupter Three interupter

During the separation of contacts, due to large fault current and high current density at the contact region the surrounding medium ionises and thus a conducting medium is formed. This is called he ARC.

Fixed contact

Moving contact

ARC

Fixed contact

Moving contact

ARCARC IS QUENCHED BY SF6 GAS

IN A CIRCUIT BREAKER

OPERATING PRINCIPLE OF CIRCUIT BREAKER

Factors responsible for arc:-

Potential difference between the contacts

Ionised particles between the contacts

By removing any one of these the arc

can be quenched.

Arc extinction through SF6 gas in circuit breaker

Factor responsible for arc resistance:-

Degree of ionisationLength of the arcCross section area of arc

Line Isolator

Circuit Breaker

Bus Bar #1

Bus Bar #2

Bus Isolator 2

Bus Isolator 1

circuit breaker connected with bus bars

1. Chemically inert

2. Non-toxic

3. Non-corrosive

4. Non-flammable

Physical & Chemical properties

5. Odourless

6.Electrical insulator

•Arched SF6 gas is poisonous.•Contribute to the manmade greenhouse effect.•Continuous monitoring devices are required.•Special facilities are required for transportation of SF6 gas.

DISADVANTAGES OF SFDISADVANTAGES OF SF66 CB CB

SF6 gas found to be greenhouse gas that causes environmental hazards

• 100% SF6 is more hazardous.• Experimentally suggest that

69%SF6 /31%N2 gas mixtures is better in circuit breaker and non-hazardous.

• Further research is going on to replace or mixture of gases for better dielectric strength without environmental problems.

LIMITATION

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 CB gas has to offer will take us to new heights in the prevalent power system.

reference HIGH VOLTAGE ENGINEERING -M.S

NAIDU,V.KAMARAJU –TheMCGraw-hillcompanies 4thedition 2009 ISBN 97-80070669284, chapter-1,2

PRINCIPLES OF POWER SYSTEM-V.K MEHTA ,ROHIT MEHTA-S.Chand &company pvt. Ltd, 1st

edition 2013 ISBN 81-219-2496-0,CHAPTER-19

WWW.ijettjournal.org

ANY QUERY

??