3.1 Introduction

Solid, liquid, and gaseous insulations have been used in the electrical industry for different apparatus. They form one of the most important components in all electrical apparatus, including Busbar Systems.

Porcelain (and glass to a limited extent) has been used as an insulator for indoor and outdoor applications ever since the commercialization of electric power. A porcelain insulator manufacturing industry requires significant capital investments. The process is labour intensive with large lead times and consequently, the products are relatively expensive. Despite that, even today, there are applications where porcelain is the only accepted insulation material. The faith and confidence that it generates in a user can be compared to a cult following. It commands and gets a premium price over other insulating materials for similar applications.

Disc Insulators made of glass have been used in transmission lines. One of the advantages of glass as an insulating material is that it can be recycled. Since water condenses on glass easily, its use is limited to specific applications and geographical areas.

Oil has been extensively used in transformers and continues to be the prime insulation medium in power & distribution transformers and high voltage instrument transformers. Oil had also been used in bulk and minimum Oil Circuit Breakers for providing insulation and efficient quenching of the arc. Oil is still used as an insulating medium in oil-filled cables (OFC) in extra-high voltage (EHV) systems. (Oil also acts as a cooling media in Power and Distribution Transformers).

Over the last century, with the demand for power increasing exponentially, there arose a need to develop a suitable insulating material, for medium voltage switchgear and instrument transformers, dry-type distribution transformers, and motors, that not only had good dielectric and thermal properties but was also suitable for moulding to different shapes to meet the requirements of supporting arrangements. Considerable research in the field over the past century in organic insulation has resulted in the development of synthetic resins (epoxy, polyester, cycloaliphatic, polyurethane) that had the desired properties. The components with new insulating materials with shorter lead times were cost-effective. The industry was quick to accept, adopt and encourage the new insulating material. Glass reinforced resin components such as dough moulding compound, sheet moulding compounds, pultrusions, and filament wound components were developed. These had excellent mechanical properties and desired dielectric properties. Composite Insulators were developed for use in outdoor service.

Consequently, the porcelain insulator manufacturing industry has seen a steady decline in its market share despite having good dielectric properties, higher temperature-withstand capability, better resistance to corrosion & ultraviolet radiation, and longer life. Composite insulators are replacing……