3.3 Glass
Disc insulators made of glass have been used in
transmission lines for the past few decades.
These have not been installed as bus support insulators either in an open bus or metal-enclosed
bus. The reason for it becomes evident when one
understands the manufacturing process.
One of the advantages of glass Insulators is that, unlike porcelain, any
component, rejected due to defects or shattering while processing can be
recycled. It is, therefore,
environmentally friendly.
The manufacturing process is highly automated. The raw material comprises sand, quartz, soda ash, calcite, feldspar, dolomite among other ingredients. Glass from the shattered and defective component called cullet, is mixed with raw material and fed to the furnace. The furnace operates at around 1280 ⁰C. Based on the shape and geometry of the finished Insulator, a predetermined volume of molten glass gob, free of impurities and bubbles, is fed into a pre-heated mould. The outer contours are shaped by a mould placed on a rotating table. The inner contours are established by stamping while the glass is still at around 1000 ⁰C. The Insulator is subjected to repeated thermal cycling, resulting in the toughening of the glass. This process automatically shatters the defective pieces which are sent for recycling.
Glass discs are then further processed with the
attachment of metallics, both at the top and at the bottom, using special
cement as the bonding material. This
process is very similar to that adopted for a porcelain disc insulator. The finished glass disc insulator has shapes
similar to that of a porcelain disc insulator.
Toughened Glass Disc Insulator (Figure - 3.3)
One of the major disadvantages of glass insulators is that moisture can easily condense on the surface. This can facilitate the deposition of dust leading to increased leakage current. Glass insulators can be coated to improve its surface properties. Glass insulators are cheaper than porcelain insulators.
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