AY: 2021 – 22

BRANCH :- Electrical Engineering

SEMESTER :-6th

SUBJECT :-S.G.P.D.

CHAPTER :- 04

TOPIC :-Sulphur Hexa Flouride Circuit Breaker

FACULTY :-Er. AKSHAY PALEI

• In this circuit breaker SF₆
• gas is taken as arc extinguishing medium.

CHARACTERISTICS OF SF6 GAS:-

• It is a highly electromagnetic gas.
• Dielectric strength of SF₆ gas is 2 to 3 times than that of air.
• It is extremely stable and inert gas.
• Heat content property at temperature below 6ooodegree kelvin is much higher than nitrogen.
• It is colourless,odourless ,non -toxic and non- inflammable gas.

CONSTRUCTION:-

• It consists of fixed and moving contacts which are hollow . The moving contact connected with moving member and connected with SF₆ gas reservoir.
• Gas is exhausted through opening of moving member.
• The fixed contact is also a hollow contacts having arcing horn.Its tips are coated with copper tungsten coating.
• Both the contacts are closed with each other at arcing chamber
• SF₆ gas is present at 2.8 kg/cm2 pressure

OPERATION

• When fault occurs moving contacts gets separated from fixed contacts there by an arc is produced.
• Since moving contact is synchronised with opening of SF₆
• valve opens and SF₆
• gas enters arc chamber at 14 kg/cm^2 pressure.
• It captures all free electron of arc path and form immobile electron.
• Hence dielectric strength build up and arc extinguishly.

ADVANTAGES:-

• Superior arc quenching property.
• Due to high dielectric strength such breaker can interrupt much larger current.
• It gives noiseless operation.
• No risk of fire in this breaker.
• Low maintenance.

DISADVANTAGES

• Cost of SF₆
• circuit breaker is high.
• Additional equipments needed for reconditioning of SF₆
• gas after every use .

USES :-

• It can interrupt 60 KA.
• Voltage ranges are 50-80 KV.
• New SF₆
• circuit breakers are designed for voltages 115 kv to 230 kv.

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