Circuit breaker

 

Circuit breakers are used in electrical installations to make or break the circuit with load or without load. They also incorpo- rate protective devices.

The circuit breaker is a switching device which also offers protection by tripping & cutting off the supply to load in case of fault. Primarily the circuit breakers are used for switching of different kinds of load in Industries, Buildings, Commercial Complexes, and Hotels, etc......

We used Capacitor for Many kind of abnormal conditions are there which exist in our electrical system that have the potential to damage the circuit & its components. These conditions are defined as 'FAULTS'.Further fault is categorized as

• Overload

• Short Circuit

• Earth

In order to keep our electrical components & system safe, it is mandatory to protect our system against the above faults. This leads to the need of circuit breaker.

types of circuit breaker regards as per voltage

LOW VOLTAGE CIRCUIT BREAKERS : 

I) MCCB (molded case circuit breaker )

iii) MCB ( miniature circuit breaker )

ii) ACB (air circuit breaker )

iv) RCCB (residual current Circuit breaker )

HIGH VOLTAGE CIRCUIT BREAKERS :

I) VCB (vacuum circuit breaker )

ii) SF6 (sulphur hexa flurried )

iii)OCB ( oil circuit breaker )

iv) ABCB (air blast circuit breaker )

MEDIUM VOLTAGE & HIGH VOLTAGE CIRCUIT BREAKERS

Voltage level from 1KV-69KV is categorized under medium & 69KV-230KV is egorized as High Voltage. Circuit Breakers operating in these voltage canges are known as Medium & High Voltage CBS respectively.

I ) MCCB :

 MCCB stands for Molded Case Circuit Breaker. It is another type of electrical protection device which is used when load current exceeds the limit of a miniature circuit breaker. The MCCB provides protection against overload,short circuit faults and is also used for switching the circuits. It can be used for higher current rating and fault level even in domestic applications. The wide current ratings and high breaking capacity in MCCB find their use in industrial applications. MCCB can be used for protection of capacitor bank,generator protection and main electric feeder distribution. It offers adequate protection whenever an application requires discrimination adjustable overload setting or earth fault protection.

ii) MCB : 

MCB or Miniature Circuit Breaker is a circuit breaker which is used for protection where current ratings are lower. It can be used upto 125A circuits

& like MCCBs it also offers protection against overload & short circuit through bimetal & solenoid. These days Class 3 MCBs are very popular due to their ability of tripping quickly & also minimum loss of let through energy.

ADVANTAGE OF MCB : 

1 . MCBs are essentially tamperproof as they have enclosures of a sealed type.

2 . MCBs afford closer protection than the re-re-wireable and HRC fuses in common use, because of the narrowly controlled tripping factor i.e. ratio of minimum trip current/rated current.

3 . MCBS can assume the function of a switch as well as a protective device and consequently they may be used to control, as well as protect, the circuits and appara- tus.

Availability of MCB : MCBs are available in-degeneous in the various combinations of poles and current ratings.

i) Single pole MCB. Current rating 5 to 60 amps. 

ii) Double pole MCB  5 to 60 amps.

 iii) Triple pole MCB  current rating 5 to 60 amps.

iv) Four pole MCB  current rating 5 to 60 amps.

difference between MCB and MCCB : 

MCB :

-- it Stan's for miniature circuit breaker

--Rated current not more than 125 Ampere

--Its interrupting current rating is under 10 ka

--Judging from their power capacities, MCB is mainly used for low Breaking capacity requirement mainly domestic.

--Its trip characteristics are normally not adjustable since they basically cater to low circuit

MCCB : 

--It stands for Molded Case Circuit Breaker.

--Rated Current up to 1600A

--Their interrupting current ranges from around 10ka to 85 ka

--MCCB is mainly used for both low and high Breaking capacity requirements mainly industrial

--Its trip current may be fixed as well as adjustable for overload and magnetic setting.

iii) ACR : 

these circuit breaker employ high pressure air blast as an arc quenching medium the air blast cools are and simplest ways the arc  produ to atmosphere 

as compressed air is used for are extention hense these are also called air circuit breaker.

Majority for circuit breaker for voltage beyond 110KV orc of this type. hense these are most suitable for high voltage . 

iv)  RCCB :

 RCCBs as the name suggests offer protection against Earth Leakage. It is

used in homes, offices & industries according to the current sensitivity   required  as per application. In case of current leakage it senses the same & trip thus   saving the human & circuit from shock & adverse effects of current leakage

HIGH VOLTAGE CIRCUIT BREAKERS: 

I) VCB : 

Vacuum Circuit Breaker or VCB is used for Medium Voltage applications. In VCB the contacts operation & arc quenching takes place inside bottles where Vacuum is present.

A vacuum circuit breaker is a kind of circuit breaker where the arc quenching takes place in a vacuum medium. The operation of switching on and closing of current carrying

contacts and interrelated arc interruption takes place in a vacuum chamber in the breaker which is called a vacuum interrupter.

Working Principle :

The vacuum circuit breaker working principle is, once the circuit breaker contacts are opened within the vacuum, then an arc can be generated among the contacts through the metal vapors ionization in the contacts. But, the arc can be quenched easily as the electrons, ions & metallic vapors are generated throughout the arc quickly condense over the outsides of the CB contacts, so the dielectric strength can be quickly recovered..

The most important feature of a vacuum is that once the arc is generated within the vacuum, then it can be extinguished quickly because of the quick improvement rate in Dielectric strength .

ADVANTAGE OF VCB :

 vacuum offers the utmost insulating strength. So it has extremely superior arc quenching properties than any other medium.

• The vacuum circuit breaker has a long life.

• Unlike Oil Circuit Breaker (OCB) or air blast Circuit Breaker (ABCB), the explosion of VCB is avoided. This enhances the safety of the operating personnel.

•No fire hazard

• The vacuum CB is fast in operation so ideal for fault clearing. VCB is suitable for repeated operation.

• Vacuum circuit breakers are almost main circuit breakers are almost maintenance-free.

• No exhaust of gas to the atmosphere and Noiseless operation.