ELECTRONIC CIRCUIT BREAKER - ECB

  

A circuit breaker is an automatically-operated electrical switch which is designed to protect an electrical circuit from damage caused by overload or short circuit.

 Used to prevent the heavy current from damaging power system components.

 Unlike fuses, normal operation can be resumed with minimal turn around time.

First ever circuit breakerà SF6 type circuit breaker in the year 1938 by Germany. Researcher:Vitaly Grosse.USA developed it in the year 1951.Researchers: Lingal, Browne and Storm .First industrial application in the                year 1953.

Circuit breakers requires to reduce arcing ie, Sparks jump for several inches in the highly ionized ambient atmosphere.

The Culprit: Arcing

Sparks jump for several inches in the highly ionized ambient atmosphere.

The high current can still damage the circuit.

Arcing is analogous to Flash-over in transmission lines.

2. Block diagram:

2.1 Frame:

·         Provides space for mounting the components & holding them in place.

·         Must withstand mechanical stresses.

·         Provides insulation & isolation path for current.

2.2 Contacts:

·         Provides a method for connecting the circuit with the system.

·         Forms a part of the isolation circuit.

Basic functions:

·         Opening

·         Closing

2.2.1 Operation: Opening

·         Spring is generally used for the purpose.

·         Opening process is faster.

·         Spring gets recoiled during Closing Operation.

2.2.2 Operation: Closing

·         Solenoid is generally used for the

            purpose.

·         Closing process is slower.

·         Force of attraction increases with reduction in distance.

2.3 Trip unit:

Opens the circuit during

·         Thermal overload  

·         Short circuit

·         Ground Fault

2.4  Arc extinguisher:

·         Circuit Breakers differ in the type arc extinguishers used in them.

·         Extinguishes an arc when contacts are opened.

3. Classification:

Based on operational voltage

·         Low voltage  circuit breakers

eg: air break circuit breaker.

·         Medium voltage circuit breakers

eg: vacuum circuit breaker.

·         High voltage circuit breakers

eg: sf6 circuit breaker.

3.1 Air break circuit breaker:

·         Quenching medium: Air at atmospheric pressure.

·         Suitable for high current interruption at low voltage.

·         Principle of high resistance is used for arc interruption.

·         Arc Quenching medium: High Vacuum.

·         Air at a pressure of 10-5 mm & below is called High Vacuum.

·         An arc formed at a small separation of 1cm can also be extinguished efficiently.

·         Contacts made of special materials.

3.3 Sf6 circuit breaker:

·         Specialty: inert, non-toxic, non flammable heavy gas.

·         High dielectric strength(2.5 times that of air)

·         Disadvantage: Decomposes at high temperature.

·         With moisture, it may spoil the parts of CB.

3.3.1 Sub categories:

·         Double-pressure SF6 Circuit breakers

àEarly type of SF6 Circuit breaker

·         Puffer type Circuit Breakers

àUses SF6 in a compressed form

4. Advantages:

·         Protect an electrical circuit from overload.

·         Protect an electrical circuit from shortcircuit.

·         Used for high speed arc interruption

·         Oil can be used for both insulation & arc extinguishing purpose.

5. Disadvantage:

 

·         Sf6 used in circuit breakers decomposes at high temperature.

·         With moisture, Sf6 may spoil the parts of circuit breaker.

·         Higher the operating voltage more is the Oil required in bulk oil circuit breaker.

6. Applications of circuit breaker:

·         UPS Equipment

·         Power Supplies

·         Small Generators

·         Entertainment Systems

·         Vending Machines

·         Office Machines

·         Telecom Power Distribution

·         Railway Signaling System

·         Automatic control systems

·         Generator sets

·         AC and DC Branch Circuit Protection

·         Power conversion systems  

7. Conclusion:

It prevent the heavy current from damaging power system components.

Unlike fuses, normal operation can be resumed with minimal turn around time.

8. References:

·         Scientific american by  robert.r.birge.

·         The lock key paraldigm  by michael  consad.