Question

Insulators are made of which material?
1. Porcelain
2. Rubber
3. Glass
4. Styrofoam

Answer 1

Correct Answer - Option 1 : Porcelain

• The most commonly used material for insulators of overhead line is porcelain but glass, steatite, and special composition materials are also used to a limited extent
• Porcelain is produced by firing at a high temperature a mixture of kaolin, feldspar, and quartz
• It is stronger mechanically than glass, gives less trouble from leakage and is less affected by changes in temperature
• The materials used for porcelain are silica 20%, feldspar 30%, and clay 50%. Porcelain has a dielectric strength of about 4–10 kV/mm.
• Glass has higher dielectric strength, but it attracts condensation and the thick irregular shapes needed for insulators are difficult to cast without internal strains.
• So that manufacturers stop making glass insulators and switching to ceramic materials.

Properties of overhead line insulators:

• High mechanical strength to withstand the conductor load, wind load, etc.
• High electrical resistance (insulation strength) to minimize the leakage currents.
• The high relative permittivity of insulating material so that the dielectric strength is high.
• High ratio of puncture strength to flashover.
• It should not be porous.