Importance of insulation for bus bars
Bus bar is a metallic strip or bar that conducts electricity in a switchboard or other electrical apparatus. It is not a structural member though its main purpose is to conduct a substantial amount of electricity. The bus bar may either be supported by insulators or it can be completely surrounded by insulators. In order to prevent accidental contact with a bus bar it must be protected by a metal earthed enclosure or by ensuring proper elevation so that it is out of reach.
The performance parameters of electrical equipment and components have become more stringent and this is reason why laminated bus bars must have resistance, series inductance and capacitance. These characteristics are also very important when solving two of the major problems faced by designers – noise and resistance. There are many different types of adhesive-coated insulations available for bus bars so that the structured layers can be laminated together. Insulation is very important because it will provide the inside and outside barrier to its installed environment. Insulations can increase capacitance and at the same time lower inductance and impedance.
Most materials used as insulators are made from glass, porcelain or composite polymer. Porcelain insulators are usually made from clay, quartz, alumna or feldspar. Glass has higher dielectric strength than porcelain but it attracts condensation. When thick irregular shapes are needed for insulators, casting is difficult without internal strains. Ceramics started to be a popular material for insulators until electric utilities switched to polymer composite materials that are composed of fiber reinforced plastic with an outer weather-shed of silicone rubber. Composites are more cost effective, lighter in weight with excellent hydrophobic capability.
Advantages of composites for insulations
Composites can be designed and engineered to provide a specific range of mechanical properties that includes tensile, flexural, impact and compressive strengths. When composites are designed with oriented reinforcement, they provide additional directional strength and flexural properties at desired locations in a single part. Composites are lighter in weight but they deliver more strength per weight than most metal alloys. Insulation like EPG sheet that is paper-based and impregnated with phenolic thermosetting resins is corrosion resistant. The resin binder system also provides long term resistance to chemical and temperature environments. Composites can be fabricated in different shapes based on the application.
Composites particularly those that are paper-based are very poor conductors which make them the best option for insulations of bus bars and other electrical equipment. Composites maintain their shape and function even under severe mechanical and environmental stresses without exhibiting the “cold-creep” characteristic of thermoplastics. However, composite technology is rather new compared to the traditional insulation materials that it is now replacing.