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Tuesday, 7 January 2020

Insulator: Introduction, Properties of Insulating materials With Advantages and Disadvantages


INSULATOR 


INTRODUCTION

  • The insulators are most important part in electrical engineering during the transmission and distribution of electric power. Insulators are used to prevent unwanted flow of current from its supporting point to earth.
  • It has property that it is high  resistive  path through  which  practically no current can  flow.  
  • In  transmission  and distribution  system, the  overhead  conductors  are generally supported by supporting towers or poles. 
  • The towers and poles both are properly grounded. So there must be insulator between tower or pole body and current carrying conductors to prevent the flow of current from conductor to earth through the grounded supporting towers or poles.


 INSULATING MATERIAL

  • The common and  main cause of failure of overhead line insulator, is flash over, occurs in between line and earth during abnormal over voltage in the system. 
  • Because of this flash over, the huge heat produced by arcing, causes puncher in insulator body. 
  • Looking forward  this phenomenon the materials used for electrical insulator, has to posses some specific properties.

 Properties of insulating material

The materials which used for insulating purpose in Transmission and Distribution  is called insulating material. For successful utilization, this material should have some specific properties as listed below-

1.Insulating materials must be mechanically strong  to carry high tension and weight of conductors.

2. Materials should be  very high dielectric strength to withstand the voltage stresses in High Voltage system.

3. For prevention of leakage current to the earth. It must have property that high insulation resistance.

4. There physical as well as electrical properties must be less affected by changing temperature


Porcelain

  • Now a days it is commonly used material for over head insulator. The porcelain is aluminium silicate. 
  • The aluminium silicate is mixed with plastic kaolin, feldspar and quartz to make final hard and glazed porcelain insulator material. 
  • The surface of the insulator should be glazed enough so that water should not be traced on it.
  • Porcelain also should be free from porosity since porosity is the main cause of deterioration of its dielectric property. 
  • Porcelain material is  also be free from any impurity and air bubble inside the material which may affect the insulator properties.
Porcelain Insulator
Porcelain Insulator



Glass Insulator

  • For transmission and distribution the most commonly and popular insulator used is glass insulator. Annealed tough glass is used for insulating purpose. 
  • Glass insulator has lot of advantages over conventional porcelain insulator.

Glass insulator
Glass insulator


Advantage of glass insulators

1.Glass insulators have very high dielectric strength compared to porcelain.

2. Its resistivity is also very high.

3. This type of insulators  has low coefficient of thermal expansion.

4. It has higher tensile strength compared to porcelain insulator.

5. As it is transparent in nature is not heated up in sunlight as porcelain.

6. Because of its transparency the impurities and air bubble can be easily detected inside the glass insulator body. 

7. Glass has very long service life as because mechanical and electrical properties of glass do not be affected by ageing.

8. And also glass is low in cost than porcelain.


Disadvantage

 1.       Moisture can easily condensed on glass surface and hence air dust will be deposited on the wed glass surface which will provide path to the leakage current of the system.

 2.       For higher voltage glass cannot be cast in irregular shapes since due to irregular cooling internal cooling internal strains are caused.



 Polymer Insulator 
  • Polymer insulator has two parts, one is glass fiber reinforced epoxy resin rod shaped core and other is silicone rubber or EPDM (Ethylene Propylene Diene Monomer) made weather sheds. 
  • Rod shaped core is covered by weather sheds. Weather sheds protect the insulator core from outside environment. As it is made of two parts, core and weather sheds,polymer insulator is also called composite insulator. 
  • The rod shaped core is fixed with Hop dip galvanized cast steel made end fittings in both sides.
Polymer Insulator
Polymer Insulator



 Advantage

1.Polymer insulators is very light weight compared to porcelain and glass insulator.

2. As the composite insulator is flexible the chance of breakage becomes minimum.

3. This insulator has lower installation cost becausof lighter in weight and smaller in size, .

4.As compared to porcelain insulator it has higher tensile strength.

5. In polluted areas you can see its better performance.

6. Due to lighter weight polymer insulator imposes less load to the supporting structure.

7. Less cleaning is required due to hydrophobic nature of the insulator.


Disadvantage

1. Moisture may enter in the core if there is any unwanted gap between core and weather sheds. This may cause electrical failure of the insulator.

2. Over crimping in end fittings may result to cracks in the core which leads to mechanical failure of polymer insulator.

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