WHAT IS THE FUNCTION OF INSULATORS

  • Insulate the conductors from each other and from the towers under highest voltage and under bad air estimate circumstance.
  • Carry the conductors under the bad estimate mechanical stresses.
Insulator materials used for overhead lines:-
  1. Porcelain
  1. Toughened glass
Although the two above materials are brittle and inelastic but it are the best materials that used to insulate the conductors. 

PIN TYPE:-


  • Used distribution as well as transmission line.
  • voltage up to 33kv.
  • Break down of the insulator occurs in either by flash over or puncture.
  • Safety factor of insulator = Puncture strength/ Flash-over voltage.
  • Safety factor of pin type insulator is about 10.


SUSPENSION TYPE:-


  • Voltage more than 33kv.
  • No. of disc connected in series by metal link.
  • Each disc designed minimum 11kv.
  • It is cheaper than pin type insulator.
  • In case of increase the voltage ratings, required for addition of discs.
  • It is generally used in steel towers.


STRAIN TYPE:-


  • It is used in dead end and corner or sharp curve, there is a greater tension.
  • Voltage up to 11kv.
  • Disc of strain insulator are used in vertical plane.

SHACKLE TYPE:-


  • Frequency used in low voltage distribution lines.
  • Used in either horizontal or vertical position.
  • Directly fixed to the pole with a bolt or to the gross arm.

WHAT IS STRING EFFICIENCY:-

String Efficiency = Voltage across the whole string/n*Voltage Across disc nearest to the conductor.

  • Greater the string efficiency, more uniform the distributor.

Method of improving string efficiency :--
  1. Using long cross-arm.
  1. Grading the insulators.
  1. Using a guard ring.