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Electrical and mechanical requirements of insulators

Short answer

Electrically, insulators need high dielectric strength, high insulation resistance, a glazed non-porous surface, sufficient creepage, and puncture strength exceeding flashover voltage. Mechanically, they must withstand tensile/compressive loads, thermal shocks, be lightweight, and resist aging.

What are the electrical and mechanical characteristics required for a good insulator used on HV transmission lines?

An overhead line insulator must keep the energised conductor isolated from the earthed tower. It must also carry the mechanical load of the conductor in all weather.

Electrical requirements

  • High dielectric strength, so it does not puncture at operating and surge voltages
  • High insulation resistance, with very low leakage current over the surface
  • A high ratio of puncture strength to flashover voltage (safety factor), so that it flashes over through air rather than breaking down internally
  • A non-porous, glazed surface free from impurities and cracks, so that moisture and dirt do not form conducting paths
  • Good performance under contamination, with enough creepage distance

Mechanical requirements

  • High mechanical (tensile and compressive) strength to carry the conductor weight plus wind and ice loads
  • Ability to withstand sudden temperature changes without cracking
  • Stable properties over time, with no ageing
  • Light weight and easy handling and installation

Porcelain, toughened glass and composite (silicone rubber) insulators are used. Glass shatters visibly when it fails, which makes inspection easy.

✓ Answer checked by Claude Opus 5.5 (high effort)

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