Circuit breakers

what is an circuit breaker ?

An circuit breaker is a switching device that can be operated automatically or manually for protecting and controlling the electrical power system. In the modern power system, the design of the circuit breaker has changed depending upon the huge currents and to prevent from the arc while operating.

How does a circuit breaker protects the circuit ?

A circuit breaker is an electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Its basic function is to interrupt current flow after a fault is detected. 

What is the main function of a circuit breaker?

The main function of the circuit breaker is to close or open the circuit when the fault is detected, thus preventing the electrical circuit from getting damage.

Classification of circuit breaker.

• Air Circuit Breaker
• SF6 Circuit Breaker
• Vacuum Circuit Breaker
• Oil Circuit Breaker
• Air Circuit Breaker
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What are Fuses and types of fuses

What is a Fuse ?

 A fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit .

It is a short piece of metal inserted in the circuit ,which melts when excessive current flows through it and thus the circuit breaks.

The fuse element is generally made up of a material having,

1.low melting point .

2.high conductivity .

3.least deterioration due to oxidation, eg. silver, copper.

Advantages of fuses.

1. It is the cheapest form protection available.

2. It requires no maintenance.

3.Its operation is completely automatic .

4.It can break heavy short circuit current with noise or smoke .

5.The smaller size of fuse element impose a current limiting effect under short-circuit condition .

6.The inverse time current characteristics of fuse make it suitable for overcurrent protection.

7.The minimum time current operation can be made much shorter than with the circuit breaker.

Disadvantages of fuses.

1.Considerable time is lost in rewiring or replacing a fuse after operation .

2.On heavy short-circuit, discriminations between fuse in a series cannot be obtained unless there is sufficient difference in size of fuse concerned.

3.The current time characteristics of fuse cannot always be correlated with that of protected apparatus.  

Types of fuses

In general fuses are classified as,

1.High voltage fuses 

2.Low voltage fuses

High voltage fuses 

This fuse has blown quickly enough so that a metal film deposited on the inside of the glass tube. At high voltages, this film can carry current. (Courtesy of Flickr) High-voltage fuses are made to prevent this conductive film from forming when the fuse blows.

Types of high voltage fuses are,

1.Expulsion HV fuse

2.Cartridge  HV HRC fuse

3.Liquid HV HRC fuse

Low voltage fuses

It is a current interrupting device which breaks or opens the circuit by fusing the element when the current in the circuit exceeds a certain value. 

1.Cartridge fuse

Types of Cartridge fuses

    a. D-type cartridge fuse

    b. Link type cartridge fuse

 Link type cartridge fuse is further classified as ,

     1. Bolted link type HRC link fuse

     2. Knife Break HRC link fuse

2. Drop out fuse

3. Rewireable fuse