Introduction
Ceramic and glass are the first material choice for medium and high voltage electrical applications, like high voltage insulators and lighting protectors. These materials have good electrical and outdoor exposure resistance without significantly deterioration. However, there are still some disadvantages of these materials, such as inability to handle certain stress, contamination in environment. These concerns encourage significant innovation in material science, especially in insulation materials and silicone rubber conductivity.
Silicone rubber is a thermoset material, its molecular structure consists of alternating silicone and oxygen (-Si-O-Si-) backbone with vinyl or methyl side groups. In 1940s, since engineers discover the thermal stability and high resistance of silicone resins, one of the earliest silicone applications is in electrical industry. The silicone electrical grease is applied to maintenance insulators in reason of its eliminate the effect of flash-over and pollution. Without regular silicone grease maintenance, insulators service life will last only from a few month to 1 year.
However, the major defects of electrical grease is the difficulty of service lief accuracy prediction. This challenge the silicone manufacturing development, alumina trihydrate (ATH) is contained in silicone polymer and naphtha solvent carrier, in order to create a highly hydrophobic surface and an additional protection layer in high electrical activity. By the 1960s, high consistency rubber (HCR) is introduced into the market, HCR improve not only electrical characteristics, but also arcing resistance.
Now days, Liquid Silicone Rubber (LSR) technology provides more benefits and features than other material options. LSR have common processing characteristics in thermoplastic and unique properties of thermoset material. Manufacturers can apply this material to produce high volume of small size parts quickly. Such as LSR coating for cable, cable accessories, and other applications.
Liquid Silicone Rubber Properties and Benefits
LSR cross-links in platinum-catalyzed reaction won’t create volatile byproducts. This cross-linked structure encourage LSR retain its properties over an extreme range of temperatures. Furthermore, the strong molecular bond of silicone and oxygen atoms prevents silicone rubber from degrading at temperature of 250℃.
Although LSR molecular structure limits its reshaping or recycling once cured, LSR provides unique features and benefits as fothe followingllowing:
Efficiency
The LSR materials is very versatile and convenient, it is an attractive material option for electrical applications. Liquid silicone rubber has higher flow-ability in injection process, and requires less energy consumption in molding process. This simplifies LSR manufacturing process in cost-efficient way. Furthermore, the LSR formulations also provide greater chemical resistance with a larger operating temperature range.
Our LSR is a ready-to-use compound, manufacturers can formulate with other materials to satisfy complicated specification requirements. In addition, its continuous development and growth make this material indispensable for high-tech and complex applications in many different industries.
Reliability
Liquid silicone rubber has various formulations for molding, curing, and manufacturing, this enables LSR manufacturers to streamline production process with consistency and quality assurance. LSR never generate undesirable odors or byproducts to contaminate the water or air.
Excellent Performance
LSR provides an easy to cure and easy to manufacture material solution. Its manufacturing process is cost-effective with consistent quality. Comparing other organic elastomer, LSR performs a wide array of physical, mechanical and chemical properties.
- Flexibility,
- Tensile and tear strength,
- Elongation,
- Durometer range,
- Chemical resistance,
- Bacteria and mold resistance,
- Transparency,
- Inertness.
The LSR materials can maintain it electrical properties consistently even in environmental conditions with temperature fluctuations and moisture. This attributes silicone rubber as great insulators for high-voltage components, transformers and other electrical equipment.
Why Use LSR in Electrical Applications?
Manufacturers in various industries are searching for eco-friendly materials to produce electrical and electronic equipment. These materials should improve functionality and performance of the insulators. In reason of, insulators are becoming smaller, less lightweight and more reliable. Liquid silicone rubber is not only consistent and dependable over longer time, but also cleaner and safer than other materials.
The primary purpose of insulation materials is separating conductors without current transferring, and protecting people from energized wires and components. Over time, electrical insulation will be deteriorated by stresses from electrical, mechanical and environmental elements. This will affect the service life of insulation materials. However, the most devastating physical elements are mechanical loads, ultraviolet radiation and vandalism. Airborne pollutants will land on insulator surfaces, lead to leakage, dry band arcing and flashover. Furthermore, windblown dirt and sand also deteriorate ceramic glaze. While LSR surfaces are less prone to erosion from these abrasive particles.
In external applications, the main concerns are airborne contamination on the insulated surface. Normally, these contaminants are produced by local environments, like ocean frog or salt spray in coastal regions. Industrial and other factors will also compromise insulation materials, reduce water resistance and diminish overall electrical permanence. LSR applications, similar to ceramic glaze, will also be influenced by contaminants’ buildup.
LSR Electrical Properties
LSR formulated specific for electrical applications have advantages over traditional materials as following:
Hydrophobicity
Water forms into droplets, rather than spreading out on the silicone surface. This will minimize flashover risk by contaminated surface, and increase silicone device reliability.
Elasticity
Liquid silicone has excellent elasticity in a larger temperature range, this enables LSR components installation and operation at sub-zero temperatures.
UV Radiation Resistance
The unique LSR molecular structure make it resistant to UV radiation permanently. LSR is a perfect material choice for external application.
Low Flammability
Silicone rubber only ignite at extreme temperature, and never release halogens or toxins in fire. It is most suitable for locations with strict fire safety standards, such as hospital, ships, trains, subway systems, high-rise buildings.
Dielectric Characteristics
The Liquid silicone rubber has higher electrical resistivity and superior dielectric strength than other insulating materials. Furthermore, these properties are unaffected by high temperature. LSR ensure a longer service life than other insulating materials in similar operation environments.
Long-term stability of LSR ensure its insulation in higher temperature, this give rise to better utilization and optimal transfer capacity. Manufacturers have developed different form of silicone, from fluids, gels to polymers, compounds. In order to formulate and customize various grades of liquid silicone rubber for different electrical applications, such as conformal coating, potting and gluing.
LSR Electrical Applications
The unique combination of silicone properties encourage LSR to be a suitable material in electrical applications:
Silicone Insulator
Electrical, mechanical and environmental stresses affect insulator service life. Airborne pollutants and moisture will form conductive film on the surface, lead to currents leakage and dry band arcing. This eventually result in contamination-based flashover and fault in electrical circuit. The leakage currents increase as insulator material surface lose hydrophobicity and water resistance.
Hydrophobicity in polluted environments is the primary property for electrical insulators. However, this hydrophobic property will decrease with surface ages from wetting and pollution. The silicone insulator surface form water in droplets rather than continuous film. Ultimately, it provides superior hydrophobic performance with little cleaning and maintenance over time.
Silicone Coating
Standard insulators have higher failure ratio as pollutant increase, silicone coating is added to failed insulators surface. In order to return their reliable operation. Traditional companies apply a layer of glass, porcelain or epoxy resin. However, these coating materials will lead to pollution flashover. Silicone coating provides a more attractive, cost-effective and long-term solution. Silicone-coated surfaces extend insulation service lief and promote more efficient maintenance management.
Cable Accessories
Cable accessories are exposed to harsh outdoor and underground environment, it requires exceptional insulating characteristics. Liquid silicone rubber is applied in such accessories to ensure permanent connection, such as cable joint terminations and connectors. LSR has favorable stress to elongation ratio, and excellent resilience, this encourages it to fit perfectly onto cable wires. These products are highly and permanently elastic over a wider range of temperatures than other materials. In reason of LSR outstanding hydrophobic property and exceptional thermal resistance, it is perfect insulating material for cable accessories.
Silicone Cable end Terminations
The liquid silicone rubber is used for two type of cable end terminations:
- Push-on design: This termination design has a polyethylene ring as space holders until placement, this silicone has hardness from 35 to 50 Shore A.
- Cold shrink design: This design apply softer silicone rubber with hardness from 25 to 30 Shore A.
There is no chemical bonds between terminal and cable, silicone elastic property will prevent trapped air in high electrical field area and around the cable perimeters.
Fire Safety Cables
The most critical requirements of fire safety cable is ensuring its continuous function and powder supply signal transmission. LSR cable can guarantee the intact powder supply in fire events.
Cable Sleeves
Metal cable enclose in LSR sleeves can benefit from the innate silicone properties, such as electrical insulation, abrasion resistance, flame retardancy, heat stability and long-term flexibility.
Conclusion
In conclusion, liquid silicone rubber has excellent electrical properties, this make is an attractive solution for fabrication of electrical devices and equipment. Its unique surface characteristics make it suitable for electrical applications in moderate or high pollution environments. In order to reduce surface leakage currents, dry band arcing and flashover.
