Advantages of Composite Insulators

Advantages of Composite Insulators are more outstanding over than porcelain and glass insulators, especially for ultra HV transmission lines, such as Light weight, Better contamination performance, and so on.

Composite insulator hydrophobicity

Advantages of Composite Insulators:
Polymeric transmission line insulators offer significant advantages over porcelain and glass insulators, especially for ultra HV transmission lines. Their light weight allows tower designs and compacting that porcelain and glass insulators do not. They can be used as phase spacers on compact lines to control galloping and to limit conductor motion due to through-faults. They have generated considerable interest among utilities, including quality control and testing requirements. Early evaluations indicated that their withstand performance was "equal to or better than that of a comparable length of porcelain insulator chain". More recent tests have generally verified these evaluations. Lack of intermediate electrodes, and small diameter, contribute to this improved performance.

The specific advantages, compared with ceramic insulators, are:
Light weight-lower construction and transportation costs.
Vandalism resistance - less gunshot damage.
High strength to weight ratio-longer spans/new tower.
Better contamination performance.
Improved transmission line aesthetics.

The reason for using composite insulators varies among utilities, but one of the most common reasons is connected with the low weight. The weight of a composite insulator is normally only about 10% of the equivalent porcelain or glass type. Composite insulators enable lighter tower designs or upgraded existing lines. Another important reason is associated with cost reduction, which would include lower cost for transport and construction, for narrower rights of way and for less maintenance. Recently, composite insulators, especially those for application in transmission lines, have actually become cheaper than counterparts made of glass and porcelain.

The use of polymeric materials instead of porcelain or glass is not understood to its fullest potential, especially with regard to their water-repellent (hydrophobic) properties. Today, composite insulators are, in many cases, pessimistically designed for a hydrophilic state. This pessimism has led to a situation wherein some of the ideas and hypotheses, formulated right at the introduction of composite insulators, have been developing extremely slowly. The shortening of specific leakage distances and better control of stresses, advantages of compacting, as well as voltage upgrading can be named as examples. At the surface, there exists insufficient knowledge on the basic phenomena regarding the long-term performance of the materials used, together with a lack of reliable testing methods for material and product assessment. Many questions remain unanswered; there is, therefore, a great need today for more research activities to cover numerous aspects pertinent to outdoor insulation:
The production and performance of new materials
The understanding of electrical, chemical, and mechanical deterioration mechanisms
The proper dimensioning, design, and manufacturing of the materials into insulators
The development of methods for monitoring the performance and deterioration of the insulators in service.

Composite insulators do not shatter, break or cause any harm to personnel in the case of misadventure. SIR is also softer than EPDM in that the sheds are pliable. This feature allows greater safety in handling the composite insulators. Also, since the weight of each insulator is less, then the packaging that it comes in is more efficient. There is less packaging, less nails protruding from cases and less clean-up and waste at site.

SIR's superior capacity to bead water, make composite insulators better than glass, porcelain and EPDM rubber. While most composite insulators demonstrate the ability to bead water when new, all but SIR insulators eventually degrade under contaminated conditions and over long periods of time. The hydrophobic properties of SIR prevent reduction in the dielectric properties of the insulation system.

Composite insulators are not subject to high leakage currents, because regardless of the amount of contamination present on the insulator, SIR can continuously bead water. This insures lower line losses and consistent flashover values over the life of the transmission line.

The remarkable qualities of SIR's leakage performance allow for a reduction by 30% of the equivalent leakage distance required for porcelain and glass. Consider the different current carrying capacities between copper and aluminum conductors of the same size. The atomic structure of SIR too changes the leakage requirements over porcelain and glass. This 30% reduction in leakage requirements can influence the design height of transmission structures, or provide a greater factor of safety on existing structures.

To prove the superiority of SIR, laboratory and field tests were conducted on composite insulators alongside equivalent porcelain and glass designs. With 30% less leakage inches versus standard porcelain designs at 230 kV, the composite insulator demonstrated flashover at voltage levels 30% higher than porcelain under the worst contamination level.

Composite insulators are designed to provide cost effective solutions for the unique as well as the everyday applications. The variety of strength ratings available enables one to select the best insulator for a given application by using higher strength where required, and reducing cost when the strength is adequate.

The mechanical load bearing element of all composite insulators is a pultruded fibreglass reinforced resin rod. Because a composite insulator is only as strong as its core rod, reliable selects only those rod materials and manufacturing processes which can provide high mechanical strength under dynamic loading conditions. Each core rod must meet stringent quality control standards for dielectric strength, glass content, and moisture absorption which ensure long consistent service life.

Recently, although polymeric materials are much more sensitive to aging than conventional porcelain and glass materials, polymeric materials are applied to insulator surfaces, because of several advantages in the field of outdoor HV insulation. One major advantage offered by polymeric materials is to impart a hydrophobicity to insulator surfaces. The hydrophobicity can prevent contaminated water films from forming on the insulator surface even in wet conditions, which contributes to a suppression of leakage current. One type of polymeric materials is applied increasingly for housings of outdoor suspension and line-post insulators, bushings, arresters, cable terminators, line-spacers and protective coatings. SIR materials of this type can maintain their hydrophobicity for a longer time, over which most polymeric materials lose their hydrophobicity and allow leakage current and flashover to develop with reduced service time due to electrical and environmental stresses such as dry-band arcing and UV radiation.

The main disadvantages of composite polymeric insulators are:
1. They are subjected to chemical changes on the surface due to weathering and from dry band arcing
2. Suffer from erosion and tracking which may lead ultimately to failure of the insulator
3. Life expectancy is difficult to evaluate
4. Long reliability is unknown
5. Faulty insulators are difficult to detect.

Composite insulator hydrophobicity:
The hydrophobicity of a polymeric insulator may influence its performance especially during wet and polluted conditions. Service experience and laboratory tests have shown that the surfaces of SIR and EPDM rubber insulators lose their initial hydrophobicity and become hydrophilic when they are exposed to prolonged dry-band arcing. The material can by exposure to wet and contaminated conditions lose its hydrophobicity due to a reorientation of the hydrophobic methyl (CH3) groups at the insulator surface. However, the SIR can recover and regain its hydrophobicity. In the past several investigations have been done on the wettability of polymeric insulators.

Once every year, all the energized insulators are manually scrutinized. During this examination the hydrophobic properties of the insulators are determined by a spraying of their surfaces with a fine mist of tap water using an ordinary spray bottle. This provides only a rough estimate of the wetting of the insulator surfaces. However, it is a suitable method for rapid and easy checking of the hydrophobicity of the insulators in the field.

During the autumn and winter the insulators are less hydrophobic than summer. This is probably due to the wet and less sunny environmental conditions prevailing during these periods of the year. Generally, the SIR insulators are less hydrophobic on the under-sides of the sheds while, on the other hand, the EPDM rubber insulators are less hydrophilic on the under-sides.

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