Porcelain insulator materials

Porcelain insulator consists of porcelain body, cap and pin and end fittings. Porcelain insulator materials include alumina porcelain, metallic fittings and cement.

Porcelain insulator materials

The insulators shall be manufactured from good quality porcelain insulating material as per approved design. The materials supplied shall be free from blowholes, flaws, cracks, or other defects and shall be smooth, close – grained and of true forms and approved dimensions. All machined surfaces shall be true, smooth, and well finished.

The porcelain shall be Ivory white, non-porous, of high dielectric, mechanical and thermal strength. The materials shall be free from internal stresses, blisters, laminations, voids, foreign matters / particles, imperfection of other defects which might in way render it unsuitable as insulator shells. Porcelain shall be unaffected by climatic conditions, ozone, acids, alkalies, zinc, dust etc.
The porcelain shells shall be made by wet process. They shall be clean, dense, homogeneous, and shall be fired to a complete and uniform verification so that glaze is not depended upon for insulation. The glaze shall be smooth, uniform and of Brown shade and shall cover completely all exposed porcelain in parts of the insulator. The shells shall posses the qualities best adopted to insulators for service at extra and ultra high voltages.

Metal fittings of drop forged steel or heat-treated malleable cast iron or Spheroidal Graphite Iron (SGI).Insulators are required to have excellent mechanical properties such as strength, toughness, high corrosion resistance, free from corona effects, etc.

Cement used in the construction of insulators, particularly for joining the metal parts with the porcelain insulator, shall not cause fracture by expansion or loosening by contraction and must have high compression and shearing strengths and be free from change in volume due to ageing and temperature changes. The thickness of the cement shall be kept as less as possible, however without affecting the strength of the joint, and proper care shall be taken to correctly fix the individual parts. The cement shall not give rise to chemical reaction with the metal fittings and/or thermal instability or chemical changes either in the porcelain insulator or the metal parts themselves.

Galvanized steel parts shall be made from high quality steel produced by either acidic or basic open hearth process, electric furnace process or basic oxygen process. All the properties of the steel castings and hard drawn shall conform to the relevant standards.

The zinc used for galvanizing shall be electrolytic high grade Zinc, not less than 99.5 percent purity. Galvanizing has to be done hot dip galvanizing process.

Porcelain insulator materials design and manufacturer shall be in accordance with ANSI and IEC specifications.


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