Tuesday, 31 March 2020

Circuit Breaker- Working Principle, Construction, Types.

Circuit Breaker
Circuit Breaker
  • The electrical circuit is an switching device that interrupts the fault current or the abnormal current. Circuit breaker is a safety device used protection of electrical equipments. 
  • It can be operated manually and automatically. It protects an electrical circuit from damage caused by abnormal or excess current from an overload or short circuit.
  • In indoor applications of Circuit breaker we also use it as an isolator.

Construction of Circuit Breaker

There are many components in circuit breakers.

1. Frame
To all the circuit breaker components frame provides the insulation. Frame is constructed by thermal set plastic such as glass polymer.

2. Contacts
Contacts are the way through which the current flows in circuit breaker. When fault current flows and circuit breaker turns off then C.B. interrupts the flow of current by seperating it's contacts.

Contacts are of two types
1. Straight-Through Contacts
2. Blow-Apart Contacts

3.Operating Handle
Operating handle is connected to the movable contacts arm through an operating mechanism. Operating handle is moved from the OFF to the ON position.

4. Trip Unit
To providing the open and close its contacts manually circuit breaker must automatically open its contacts when fault current is sensed. It determines when the contacts will open automatically.

Construction of Circuit Breaker

Construction of Circuit Breaker

Working Principle of Circuit Breaker

  • A circuit breaker sense the electrical current flowing through it and breaks that current if current exceeds the limit that is abnormal current.
  • There are two common ways that circuit breaker sense the current Thermal and Magnetic
  • Small breakers are usually thermal and work by passing the current through a heating element and break the current if that element gets too hot.
  • In simple terms, it's a switch which turns itself off. Its just two metal contacts which can be moved apart, like any other switch and a solenoid which is an electromagnetic device which moves one of the contacts. 
  • The solenoid is calibrated so that at a certain electrical current it activates and turns the switch off. 
  • When a circuit has a breaker in it and the circuit tries to draw more current than it can handle it turns off and deactivates the whole circuit once the problem with the current is fixed, we can turn the switch back on, and the circuit is fine again. 

Types Of Circuit Breaker 

  • Circuit Breakers are mainly classified on the basis of rated voltage.
  • Circuit breaker below the rated voltage of 1000V are the Low Voltage Circuit Breakers and above the voltage 1000V are the High Voltage Circuit Breakers.
  • They are mainly classified on basis of the medium of arc extinction are following.

1. Oil Circuit Breaker 
2. Bulk Oil Circuit Breaker
3. Minimum Oil Circuit Breaker
4. Minimum Circuit Breaker
5. Air Blast circuit Breaker
6. Sulphur Hexafluoride Circuit Breaker
7. Vaccum Circuit Breaker
8. Air break Circuit Breaker

Friday, 6 March 2020

Types of Fuses and Classification

  • In Electrical or Electronic Engineering the fuse is used for safety of the devices. The fuse is usually an electronic device, which is used to protect circuit from over current, overload and make sure the protection of the circuit.
  • Is composed of an alloy which has a low melting point. The strip of this fuse is placed in series with circuit.
  • The fuse is mainly classified into two types. And depending on the input supply voltage they are classified in AC fuses and DC fuses. AC and DC fuses are again classified are following. 
Classification of Fuse
Classification of Fuse

AC Fuses

  • In AC system, there is easy to extinguish the arc produced due to the over current because in AC system the voltage is with 50 to 60 Hz frequency and it changes its amplitude from 0 to 60 in one second. 
  • Because of this AC fuses are little small than DC fuses. AC fuses are again classified in Other types.

DC Fuses

  • In DC system, because of over heating when the metallic wire melts and arc produces and it is very difficult to extinguish this arc due to the DC constant value.
  • In order to minimize the fuse arcing the DC fuses are bigger than the AC fuses.  

Rewirable Fuse

Rewirable Fuse

Rewirable Fuse

  • This kind of fuse is most commonly used in the case of domestic wiring and small scale usage. Another name of this type of fuses is kit-kat type fuse. 
  • The main composition is of a porcelain base which holds the wires. The fuse element is located inside a carrier that is also made out of porcelain. It is possible to remove the fuse carrier without any risk of electric shock. 
  • The main advantage of this type of fuse is that it is easy to install and also replace without risking any electrical injury. 

Cartridge Fuse

Cartridge Fuse
Cartridge Fuse
  • Cartridge fuses to protect many of the electrical appliances such as motors air-conditions, Pumps, Refrigerators, etc. It was developed to overcome the disadvantages of the former. 
  • The fuse wire is enclosed in a glass tube, with two metal caps at both ends. So the fuse element does not deteriorate. Replacement is expensive. This fuses are available 600A and 600 V AC and has used for Industries, Commercial Area.
  • This fuses are of two types 
                                         1.D- type cartridge fuse and 
                                         2. Link type cartridge fuse

1. D- Type cartridge Fuse
  • This can not be interchanged and comes with the fuse base and cap, adapter ring, and the cartridge. The main feature of this fuse is its reliability. 
2. Link type cartridge fuse or HRC High Rupturing Capacity Fuse

HRC Fuse
HRC Fuse

  • The link type cartridge fuse is also called the HRC fuse means High Rupturing Capacity fuse. The fuse wire or element can carry short circuit heavy current for a known time period. 
  • During this time if the fault is removed, then it does not blown off otherwise it blow off and melt. The enclosure of fuse is either of glass or some other chemical compound. 
  • The Operation of HRC fuse is that when the over rated current flow through the fuse element of HRC fuse the element is melted and vaporized. 
  • The filling powder is of such a quantity that the chemical reaction between the silver vapor and filling powder forms a high resistance substance which very much helps in quenching the arc.

High Voltage Fuse
  • All fuses used in power system from 1.5kV up to 138 kV are categorized as high voltage fuse. High voltage fuse are classified to protect instrument transformer used for electricity material, or for small power transformer where the expense of a circuit breaker is not warranted. 
  • When the fuse blow, heat from the arc causes the boric acid to evolve large volume of gases. The associated high pressure and cooling gases rapidly quench the arc. High voltage fuses rated for more than 1500V and up to 13kV.

Monday, 2 March 2020

Electric Fuse and Why are Fuses used? Working, Types, Applications

Electric Fuse 

  • In Electrical or Electronic Engineering the fuse is used for safety of the devices. The fuse is usually an electronic device, which is used to protect circuit from over current, overload and make sure the protection of the circuit. 
  • An electrical fuse operates on the principle of heating effect of electric current. There are many types of fuse elements available but function of most of these fuses is the same. 
  • Ordinarily, a fuse is a short metal wire or strip, connected to a conductor on each end, and usually enclosed in a glass or other non conductive container.  The fuse is mostly used for protection purposes in residential.

Electric Fuse
Electric Fuse

Working Of Fuse

  • During normal operating condition, the current flowing through the fusing element is such that the rate of heat production in the fuse element is nearly equal to rate of heat dissipation from the fuse element and thereby they are will be no considerable increases of temperature of that fuse element.
  • It usually consists of a low resistance metallic wire enclosed in a non combustible material. 
  • Whenever a short circuit, over current or mismatched load connection occurs, then the thin wire melts because of the heat generated by the heavy current flow. 
  • This disconnects the power supply from the connected system. In normal operation of circuit, fuse wire is just a low resistance component and does not affect the normal operation of system connected to the power supply. 
  • In order to minimize the fuse arcing, DC fuses tends to be bigger than an AC fuses which increases the electrodes  to reduce the arc in the Fuse.

Why they are used?

  • Whenever there is a short circuit, overload or earth fault in the system, huge current starts flowing through the system conductor which leads to hide temperature rise of the conductor itself. 
  • If this huge current is not prevented, after certain time the heat generated from the conductor part is so high, it can melt the conductor itself along with damage the insulation parts of the equipment.
  • Even there may be a chance of fire hazard due to extremely high temperature in the system. As a whole  there will be permanent damage in the equipment.
  • To prevent this, the huge short circuit current should be allowed to flow through the system for very short time so that there would be any serious temperature rise. 
  • Actually during fault nobody can prevent the flowing of  huge over current through the system but the during of flowing of this huge over current can be limited by using electrical fuse.

Types Of Fuses

Fuses can be divided into two main categories according to the types of input supply voltage.
  1. AC Fuses
  2. DC Fuses

1. Ac Fuses
  • In the AC system voltage frequency changes its amplitude from zero to 60 times every second, so arc can be extinct easily. 
  • AC fuses are little bit small in size as compared to DC fuses. 

2. DC Fuses
  • In DC system when the metallic wire melts because of the heat generated by the over current, then then arc is produced and it is very difficult to extinct this arc because of DC constant value.
  • So in order to minimize the fuse arcing, DC fuse are bigger than the AC fuses which increases the distance between the electrodes to reduce the arc in the fuse.

Applications of Fuses

Fuses are used in many industrial electrical and electronic devices for protection 
  • Hard Disk Drives
  • Laptops
  • LCD Monitors
  • Automotive Systems
  • Battery Packs
  • Gaming Systems & Portable Electronics
  • General Appliances and Devices
  • Cell Phones
  • Printers/ Scanners

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