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Friday, 10 April 2020

Miniature Circuit Breaker (MCB)- Construction, Working, Advantages, Applications.

● Miniature Circuit breaker. It also called as MCB. A circuit breaker is a switching (On/Off/Trip) device that is used for switching on and off the load and for inturreting the circuit under the fault condition.

● Circuit breaker make or break a circuit doing normal conditions. During the unhealthy conditions they break the circuit to prevent the spread of fault to other equipments.

Miniature Circuit Breaker
Miniature Circuit Breaker


● Circuit breaker is safety device used to protect your electrical appliances at home in case of short circuit or any other cause for excessive current. It operates manually as well as automatically.

● Circuit breaker have to be simple, because they are a minor safety measure in common haosehold and in the electrical grids.

Construction of MCB

There are any parts are arranged in circuit breaker.

Construction of MCB
Construction of MCB 


External casing
External casing is the insulation which hold all the components and protects them from the durt and dust.

Knob
Knob is the switch which used to turn on and off the MCB.

Contacts
There are two contacts inside the circuit breaker one is fixed contact and other is movable contact.
https://www.electricalyukti.com/2020/04/sf6-circuit-breaker.html?m=1
To hold the contacts under the spring tension when MCB is ON position.

● Bimetallic strip
The bimetallic strip used to offer delayed overload protection by sensing the flow of current greater than its rated current.

Solenoid
Solenoid provides instantaneous protection against short circuit by releasing the mechanical latch.

Arc chutes
It is used for the splitting and quenching the arc.

Working of MCB

● There are two types of operation of an MCB. The first depends on the thermal effect of overcurrent.

● Thermal Effect
When the over current flows through the MCB the bimetallic strip present in MCB owing to the thermal expansion of metals is heated and deflects by bending.

● That deflection in the strip releases a mechanical latch and this operates the contacts of the MCB to connect the fault circuit.

● Electromagnetic Effect
In the short circuit conditions the fault of sudden rising of current causes electromechanical displacement of the plunger connected with the tripping coil or the solenoid of MCB.

● Then plunger strikes the trip level with the causing of immediate release of the latch mechanism consequently so the circuit breaker contacts gets open.


Advantages of MCB

● We can identify tripped MCB even in darkness.

● It gives trip free mechanism- cannot be switched back on while fault exists.

● It also acceptable as a isolator.

● There is no any wire to replace like fuse.

● Normally it do not requires replacement.

● They act and open the circuit in less than 5 milliseconds.

● Supply is restored by resetting it again.

● It requires less maintenance and it is more reliable.

Disadvantages of MCB 

● The MCB is costly than fuse.

● The cost of MCB distribution board is greater than desirable fuse board.

Applications of MCB

● New constructions uses MCB instead of the older type fuses.

● It is designed to protect the houses from circuit overload.

● Can be used for ground fault or arc fault mechanisms.

● Domestic appliances, power supplies, lighting circuits and motor circuits etc.

Sunday, 5 April 2020

What is SF6 Circuit Breaker? Working, Construction, Advantages, Applications

Circuit Breaker in which SF6 gas under pressure is used to extinguish the arc is so it is called SF6 circuit breaker.

SF6 means Sulphur Hexafluoride gas. It has excellent dielectric, arc quenching, and other physical properties. So this is used in circuit breaker.

SF6 circuit breaker are used in high voltage transmission and distribution systems. Because it has excellent arc breaking capacity.  In this there is no risk of fire or explosion. 

SF6 Circuit Breaker
SF6 Circuit Breaker


Construction of SF6 Circuit Breaker


Construction of SF6 circuit Breaker
      Construction of SF6 circuit Breaker

The construction of SF6 circuit breaker is simple in kind of other 
Circuit breakers. There are main two contact and fixed contact. 

This two contacts are placed in the interruption chamber. Then the SF6 gas is reservoir is connected to that interruption chamber. 

When the contacts of CB opens then it allows to high pressure SF6 gas from reservoir to flow towards the interruption chamber. 

Both the contacts and arcing horn are coated with the copper tungsten material which is arc resistant material. 

This contacts are fixed like hollow cylindrical shape. Moving contacts contains rectangular which has holes in sides to allow the SF6 gas go through these holes flowing and across the arc.

This gas is recycled and reused by the suitable auxiliary system after every operation or use of breaker. This is because of the SF6 gas is costly.

Working Of SF6 Circuit Breaker

  The contacts of circuit breaker are closed at the normal operating condition of working.

When some fault occurs in the system contacts are open and arc is struck between them.

The movement of moving contacts cause to occur operate valves at the same time which enters the high pressure SF6 gas in the arc interruption chamber at some pressure.

This SF6 gas absorbs free electrons in the arc path and forms ions that ions does not carries the charge. This ions increases the dielectric strength of the gas and hence the arc get extinguished. 

This gas is stored in low pressure reservoir and this is pulled back to high pressure reservoir for reuse it.

Advantages of SF6 Circuit Breaker

 The atmospheric conditions does not affects on the performance of the SF6 circuit breaker.

The cost of it is less due to compressed air system is required.

Maintanence of this circuit breaker is less.

  It has high dielectric strength so the electric clearance gets reduced.

Arc gets extinguished at natural current zero so there is no voltage problem. There is no risk of fire.

The gas used is non-inflammable and it has chemically stable.

  Same gas is re- circulated into the circuit there by reducing the requirement of SF6 gas.

The SF6 CB can  perform various duties like clearing short line faults, opening unloaded transmission line, capacitor switching transformer reactor switching etc. Without any problem.


Disadvantages of SF6 Circuit Breaker

The parts in CB needs more cleaning during periodic maintenance under clean and dry environment.

It causes failure when the moisture enters in CB.

The SF6 gas is too costly and it needs more facility for transformation and maintanence of quality of gas.

 Arced SF6 gas is poisonous and should not be inhaled.

Applications of SF6 Circuit Breaker

  Used for high voltage Applications

For switching related to high voltage and extra high voltage applications.


Friday, 3 April 2020

What is Vaccum Circuit Breaker? Working, Construction, Advantages, Application

Vaccum Circuit Breaker (VCB) arc quenching takes place in vaccum medium. 

All operations of switching that is on and closing of current carrying contacts are take place in vaccum chamber present in the circuit breaker so it is called vaccum circuit breaker.

Vaccum offers the highest insulation strength it has for superior arc quenching properties than the other medium. 

Vaccum Circuit Breaker
Vaccum Circuit Breaker


Construction of Vaccum Circuit Breaker

Construction of the vaccum circuit breaker is simple than the other circuit breakers. 

There are main three components are arranged in VCB i.e. fixed contact, moving contacts, and arc shield. This all components are fixed inside the arc interrupting chamber. 

The fixed and moving contacts of the breaker are placed inside the arc shield. The moving contacts of circuit breaker are move through a distance of 5 to 10 mm but it depends upon the operating voltage. 

Cross arm section of Vaccum Circuit interruption
Cross arm section of Vaccum Circuit interruption


From the stainless steel the metallic bellows are formed and this metallic bellows used to move the moving contacts. 

The ability of VCB is depends on the life of the all components are made and their arrangement it requires the repeated operations satisfactorily. 


Working Of Vaccum Circuit Breaker

When the contacts of the breaker  are opened in vaccum, an arc is produced between the contacts by the ionisation of metal vapours. 

However, the arc is quickly extinguished because of the metallic vapours, electrons and ions produced during arc rapidly condense on the surface of the CB constants resulting in quick recovery of dielectric strength. 

Cross arm section of Vaccum Circuit interruption Electrons and ions produced during arc are diffused in a short time and seized by the surface of moving and fixed members and shields. 

Arc get quickly extinguished due to the fast rate of recovery of dielectric strength in vaccum. 

Advantages Of Vaccum Circuit Breaker

Vaccum Circuit breaker has excellent recovery. 

For only half cycle less arcing occurs after the proper contact separation. 

It does not requires the aditional filling of Air or oil in it.

Breaker unit is compact and self contained.

Requires less maintanence.


Disadvantages of Vaccum Circuit Breaker

Loss of vaccum occurs because of transit damage 

It requires surge suppressors for the interruption of low magnetizing current in a certain range.

Applications of Vaccum Circuit Breaker

Industrial application where the high speed making switches requires because of VCB has excellent recovery.

It is also usefull for system which requires voltage from 11 to 33 KV.


Thursday, 2 April 2020

Air Circuit Breaker- Working Principle, Construction, Types, Advantages, Applications

It is an automatically operated electrical switch which protects the system or device from any fault overload or short circuit. It protects to the Electrical equipments.

If fault is detected by the circuit breaker it interrupts the flow of current and protects to the system and for the interruption it uses air that's why it is called Air Circuit Breaker.

Air Circuit breaker used compressed air to blow out the arc. It operates in air at atmospheric pressure. 

Air Circuit Breaker
Air Circuit Breaker

Working Principle of Air Circuit Breaker

Working principle of this circuit breaker is different from the other circuit brekers in some manner. For interrupting arc it creates an arc voltage in excess of the supply voltage.

When fault occurs in any part of the system the trip coils of the circuit breaker get energised and the moving contacts are pulled apart by some mechanism thus opening the circuit.

  When the contacts of circuit breaker are seperated under fault conditions, an arc is struck between them. The current is thus able to continue until the discharge ceases.

  The production of arc not only delays the current interruption process but it also generates enormous heat which may cause damage to the system or circuit breaker itself.

The circuit breaker increases the arc voltage by three ways
1. It may increases the arc voltage by cooling the arc plasma. If temperature of arc plasma decreases then the mobility of particle in arc plasma reduces. So that's why more voltage gradient is required to maintain the arc.

2. It may increases the arc voltage by lenghning the arc path.

3. Another one way is splitting up the arc into many series arcs also increases the arc voltage.

Construction of Air Circuit Breaker


Construction of Air- Blast circuit Breaker
Construction of Air- Blast circuit Breaker 


  The air circuit breaker consists of three types of contacts in a compressed air chamber.

1. The main contact-
This main contact carries the load current. They are made up of good conducting material, such as silver or copper.

It avoids over heating of the contacts while in service.

2. Arcing Contacts Of ACB-
It is made up of harder material which has high resistance such as tungsten.

When main contacts opens the arching current flows through the arching current with high resistance path.

3. Arching horns and chutes -
Arcing horns carries the arching current so they are made up of the high resistance and from harder material.

Chutes are made up of fire proof insulating materials because there are the last contact arc.

Cooling metal plates are connected to the chutes to convert the hot gasses and gives the way and cool the contacts arc the extinction of arc.

These all components are filled in circuit breaker chamber with compressed air which acts as dielectric material.


Types of Air Circuit Breaker

There are main four types of ACB.

1. Plain Break type air circuit breaker or cross blast air circuit breaker.

2. Magnetic blowout type air circuit breaker.

3. Air chute air break circuit breaker..

4. Air blast circuit breaker.(ABCB)


Advantages

• This is cheap and free available of the interruption medium.

• ABCB are chemically stable.

• Gives high speed operation.

•  It requires less maintenance.


Disadvantages


• Current chopping problem occurs.

• Produces high noise.

• Problem of restraining voltage.

• Compressor plant requires some maintanence.


Applications

• Used for protection of plants.

• Protection of electrical machines.

• For the protection of transformer, capacitor, generator.

• For low and high voltage and current applications.



Wednesday, 1 April 2020

Oil Circuit Breaker- Working Principle, Construction, Types, Advantages


• Circuit Breaker is device used to break circuit during load in on and due to load current flow in the circuit.
• Oil Circuit breaker is breaker used to break the circuit when abnormal voltage appears and it will protects electrical equipments from abnormal voltage.
• Oil Circuit breaker is used for two purposes one is arc quenching medium and other is for cooling purpose.

Oil Circuit Breaker
Oil Circuit Breaker 

Working Principle Of Oil Circuit Breaker

• Oil Circuit breaker is used as arc quenching medium and for cooling purpose.
•  As the time of arc oil absorbs heat and split into ions and molecules and releases gases hydrogen, ethane etc.
• Which releases high amount of hydrogen gas which leads to turbulence (force) of the oil the length of the arc increases and resistance of the arc decreases but as we know resistance is inversely proportional to the current finally arc will be extinction.
• The arc extinction is occured mainly by two purposes
•  Firstly the hydrogen gas has high heat conductivity and cools the arc thus aiding the de-ionization of the medium between the contact.

• Second the gas sets up turbulence in the oil and forces it into the space between contacts, thus eliminating the arcing products from the arc path.
Thus arc extinguish and circuit current interrupts.


Construction of Oil Circuit Breaker

Construction of Oil Circuit Breaker

• It consists of current carrying contacts enclosed in a strong weather tight earth tank.
• That tank is filled with oil that is transformer oil. The oil acts as arc extinguishing medium and as an insulator between the live part and earth.
•  At the top of oil, air is filled in the tank which acts as cushion to control the displaced oil on the formation of gas around the arc.
• Oil Circuit Breaker consists gas outlet which is fitted in the tank cover for the removal of the gases.

Types of Oil Circuit Breaker

There are main two types of the oil Circuit breaker are following

1. Bulk oil Circuit breaker
Bulk Oil Circuit Breaker is again classified into two types
a. Plain break oil Circuit breaker
b. Arc Control Circuit Breaker


Bulk oil Circuit breaker
Bulk oil Circuit breaker


Minimum Oil Circuit Breaker
Minimum Oil Circuit Breaker


Advantages Of Oil Circuit Breaker

• Oil has good insulating properties which keeps arc formation to a minimum when the breaker is open or closed.
• Oil has high dielectric strength.
• Oil absorbs arc energy while decomposing.
• Good cooling property of the gas formed due to the decomposition.
• It acts as an insulator between the live parts and earth.

Disadvantages of Oil Circuit Breaker

• It takes long arcing time.
• It do not permit high speed of interrupt.
• Arc interruption control can be obtained only by increasing length of arc.


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