A presentation on Circuit Breaker

By Priyankar Misra

EEE VITAM

Introduction

• Automatically operated electrical switch, protect an electrical switch from overload or short circuit

• Basic function-fault detection and interrupt current flow

• Can be reset to resume application• Available in a variety of size

Origin

• Early form, developed by Thomas Edison in 1879 patent application-to protect lighting circuit wiring from accidental short circuit

• Modern miniature circuit breaker ,patented by Brown, Boveri and Cie in 1924.

Operation

• A fault condition must be detected• Once fault detected, contacts within circuit

breaker, some mechanical stored energy stored in the circuit breaker and some energy utilized from the fault current.

• Circuit breaker contacts carry the load current without getting heated

• Arc in generated, which is controlled and extinguished in a controlled way

Arc interruption

• Low voltage MCB-air, larger ratings –metallic or non metallic arc clutches

• Gas circuit breakers-dielectric strength of sulphur hexafluoride

• Vacuum circuit breakers-minimal arching• Air circuit breakers-compressed air

Short circuit current

• Circuit breakers-rated-normal current they can carry and maximum short circuit current they can safely carry

• Under short circuit conditions-current much larger then normal currents flow-electrical contacts open to interrupt large current arc is produced

Types of circuit breakers

• Low voltage circuit breakers• Magnetic circuit breakers• Thermal magnetic circuit breakers• Common trip breakers• Medium voltage circuit breakers• Sulfur hexafluoride high voltage circuit breakers• Disconnecting circuit breakers• Carbon dioxide high voltage circuit breakers

Low voltage circuit breakers

• Common in domestic, industrial and commercial applications-include MCB(type B, type C and type D) and MCCB.

• Characteristics –given by international standards-often installed in draw out enclosures-also made for DC applications

Magnetic circuit breakers• Magnetic circuit breakers-

solenoid-pulling action increases the current

• when current increases beyond rated-solenoid’s pull releases the latch-contacts open by spring action

• Some magnetic circuit breakers-incorporate a hydraulic time delay-during overload fluid restricts solenoid motion-permitting short current surges

Thermal magnetic circuit breakers• Mostly found in

distribution boards-use both techniques –electromagnet responding instantaneously to large surges in current, bimetallic strip responding to less extreme but longer term over current conditions

Common Trip breakers• Supplying a branch circuit-more

than one live conductors-when one pole trips all live conductors must be interrupted.

• Either contain two or three tripping mechanism-two pole common trip breakers are common on 120/240 volt system, three pole common trip breakers are used to supply three phase electric supply to large machines

• Two or four pole breakers may be used-to disconnect multiple phase ac or neutral wire

Medium voltage circuit breakers• Rated between 1-72 KV,

operated by current sensing protective relays operated through current transformer.

• Classified according to the medium used to extinguish the arc- vacuum circuit breakers, air circuit breakers and sculpture hexafluoride circuit breakers

High voltage circuit breakers• Protect and control electrical

power transmission-usually 72.5 KV or higher-mostly solenoid operated with current sensing relays operated through current transformers

• Broadly classified according to the medium used to extinguish the arc-bilk oil, minimum oil, air blast, vacuum, sulphur hexafluoride, carbon dioxide

Sulphur hexafluoride high voltage circuit breakers

• Uses contacts surrounded by sulphur hexafluoride to quench the arc, often used for transmission level voltages and may be incorporated into compact gas-insulated switchgear

• In cold climate supplemental heating or de rating of the circuit breakers may be required

Disconnecting circuit breakers• High voltage circuit

breaker, modeled after sulphur hexafluoride circuit breaker

• Disconnecting function integrated in the breaking chamber, increases the availability, reduces the space requirement within the substation, increases the reliability.

Carbon dioxide high voltage circuit breakers

• Works on the same principle as sulphur hexafluoride circuit breaker, can also be produced as a disconnecting circuit breakers, high voltage breaker

• Possible to reduce nearly 10 tons of carbon dioxide emissions during the product’s life time

Advantages of circuit breaker

• Disconnect the entire load instead of a single load

• Provide better protection to 3 phase motors• Less cost• Provides greater reliability and safety• Cost of ownership

Disadvantages of circuit breakers

• Initial cost is high• Reacts less quicker than a fuse• More sensitive to vibration and movement

Conclusion

• Circuit breaker is an essential part of electrical network as it protects every device from electrical damage

• Helps us to detect the fault and the area associated with it

• Nowadays vacuum and sulphur hexaflouride circuit breakers are widely used due to their reliable and fast operations