line insulators.pptx - Overhead Line Insulators Sag and Corona PROF ABINASH SINGH ASSISTANT PROFESSOR DEPTT OF ELECTRICAL ENGG PUNJAB ENGG COLLEGE

line insulators.pptx - Overhead Line Insulators Sag and...

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Overhead Line Insulators, Sag and Corona PROF. ABINASH SINGH ASSISTANT PROFESSOR DEPTT. OF ELECTRICAL ENGG. PUNJAB ENGG. COLLEGE, CHANDIGARH
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Introduction The overhead line conductors should be supported on the poles or towers in such a way that currents from conductors do not flow to earth through supports i.e., line conductors must be properly insulated from supports. This is achieved by securing line conductors to supports with the help of insulators. The insulators provide necessary insulation between line conductors and supports and thus prevent any leakage current from conductors to earth.
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Properties of a good insulator High mechanical strength in order to withstand conductor load, wind load etc. High electrical resistance of insulator material in order to avoid leakage currents to earth. High relative permittivity of insulator material in order that dielectric strength is high. The insulator material should be non-porous, free from impurities and cracks otherwise the permittivity will be lowered. High ratio of puncture strength to flashover
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Types of Insulators Pin type insulator Suspension type insulator String insulator Shackle insulator Stay insulator
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Insulator Failure Causes Insulators are required to withstand both mechanical and electrical stresses. The latter type is primarily due to line voltage and may cause the breakdown of the insulator. The electrical breakdown of the insulator can occur either by flash-over or puncture. In flashover, an arc occurs between the line conductor and insulator pin (i.e., earth) and the discharge jumps across the air gaps, following shortest distance. In case of flash-over, the insulator will continue to act in its proper capacity unless extreme heat produced by the arc destroys the insulator. In case of puncture, the discharge occurs from conductor to pin through the body of the insulator. When such breakdown is involved, the insulator is permanently destroyed due to excessive heat. In practice, sufficient thickness of porcelain is provided in the insulator to avoid puncture by the line voltage. The ratio of puncture strength to flashover voltage is known as safety factor. It is desirable that the value of safety factor is high so that flash-over takes place before the insulator gets punctured. For pin type insulators, the value of safety factor is about 10.
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Pin type Insulator The pin type insulator is secured to the cross-arm on the pole. There is a groove on the upper end of the insulator for housing the conductor.
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  • Fall '16
  • Rintu khanna

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