A complete silicone rubber program for all types of products

High voltage products with composite insulators

� ABB

Silicone rubber insulation possesses unique properties. It is the fastest growing, and most dominant polymeric insulation material for high voltage products. Installation of high voltage apparatus with silicone rubber insulation, e.g. surge arresters, bushings, circuit breakers, instrument transformers, and capacitors, is increasing all the time.

Water on the surface stays as droplets and does not form a continuous film. Therefore any leakage current along the insulator surface is strongly suppressed.

The mechanism behind the hydrophobicity of silicone rubber is the diffusion of low molecular weight, LMW, silicones from the bulk of the mate-rial to the surface. The LMW silicone forms a layer on the surface that is hydrophobic.

Provided they are new, polymeric materials other than silicone rubber may also exhibit hydrophobic properties. However, these materials, they normally lose their hydrophobicity after a relatively short time in service.

Flashover resistanceThe efficient suppression of leakage currents means that the risk of flashover is reduced compared to porcelain insulators.

Leakage current controlThe polymeric insulation material used for ABB high voltage equipment is silicone rubber. Depend-ing on the application either high temperature vulcanizing, HTV, silicone rubber or liquid silicone rubber, LSR, is used. Due to the chemical nature of silicone rubber, the insulator surface is hydrophobic (non-wetting).

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Change in hydrophobicity during artificial ageing test

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Leakage current over time at salt fog test

�ABB

Erosion resistanceIt is inevitable that even silicone rubber will show some discharge activity in the event of severe pol-lution, thought it is less than for non-hydrophobic material such as porcelain and EP-rubbers. With correct material formulation and a suitable insulator design such discharge activity can be minimized.

In most cases the silicone rubber used for ABB high voltage equipment is further protected by aluminum trihydrate, ATH, which has a proven arc and fire resistance capability.

The ageing resistance of ABB silicone insulation has been verified by accelerated ageing tests like the 1 000 h salt fog test and the 5 000 h cyclic test.

UV stabilityNatural UV radiation from the sun has wave-lengths of over 300 nanometers. Shorter and more energetic wavelengths are filtered out in the atmos-phere. Silicone has its maximum absorption below this wavelength, which ensures superior stability against UV radiation.

Additional advantagesThe low weight of silicone insulators compared to porcelain offers advantages in terms of earthquake resistance capability. Installation is also made easier by the fact that there is less need for strong heavy supports. As silicone rubber is non-brittle, the risk of damage to sheds during transport, installation and service is reduced. The risk of explosion and the scattering of dangerous pieces is also reduced.

Max. absorption of Si-O2 bond

Solar radiation

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Wavelength, nm290 300 400

Silicone has its maximum absorption of UV radiation below the natural wavelengths of over �00 nm.

Vandalizing test: A � kg cement block, thrown at an impact velocity of 10 m/s. No remaining damage could be seen after the test.

� ABB

Products and design

Live tank circuit breakers Demands on insulators used for gas-insulated live tank circuit breakers are high with respect to me-chanical properties as well as withstanding decom-posed SF6 gas and the heat produced during current interruption.

The glass fibers on the inner surface of the hollow insulator are protected from the effects of SF6 de-composition products by an epoxy liner reinforced with polyester fibers.

ManufacturingDuring production two major manufacturing processes are used, molding and the patented helical extrusion. To achieve the desired properties for the insulation molded designs are used for surge arrest-ers and the DryQ capacitors.

For circuit breakers and instrument transformers helical extrusion molded insulators minimize elec-trical field concentrations and reduce any build-up of contamination.

The technique uses extrusion of the shed profile together with the sheath. The turns are compressed to each other and to the tube in the uncured stage in such a way that it does not leave any voids. The composite insulators are type and routine tested in accordance with IEC 61462.

Metal flange

Glass fiber reinforced epoxy tube

Liner

Silicone rubber shed

Conceptual sketch of a hollow composite insulator with silicone rubber insulation

�ABB

Instrument transformersWe can offer most of our instrument transformers with the patented helical extrusion molded silicone rubber insulation.

The design for these insulators is the same as for circuit breakers, i.e. a hollow composite insulator with extrusion molded silicone rubber sheds.

Explosion resistant designs improve personal safety.

Surge arrestersABB has also chosen to use silicone rubber insula-tion for surge arresters. This produces the added benefits of low weight, improved pollution per-formance, increased personal safety and flexibility during the erection process.

The PEXLIM family of ABB silicone-housed arresters comes in two different designs, the molded design and the high-strength tubular design. The silicone rubber insulation makes the surge arrester explosion proof, which increases personal safety.

Capacitors The dry type capacitor, DryQ, exploits the advan-tages of polymers in its capacitor housing. Silicone sheds are molded as external insulation. Connec-tions are made at both ends of the capacitor, which means that no special bushings are required.

The DryQ capacitor is smaller and lighter than conventional capacitors and thus easier to handle, during both transport and installation.

IMB PEXLIM Q DryQ

� ABB

Field experience

Field test To gain information on long-term behavior in respect of optimal creepage distance of HV appara-tus in different environments test installation have been made. A number of surge arresters, bushings and circuit breakers with composite insulators using silicone rubber as external insulation have been installed at different sites. These have been subjected to heavy or very heavy pollution levels for a test period of up to seven years.

The test stations were chosen to represent all possible climates, including coastal, subtropical and desert areas.

The results, presented in a Cigre’ report, verify the improved hydrophobicity and low leakage current properties of composite insulators. With regard to pollution performance, the short-term and long-term hydrophobicity characteristics of silicone rubber apparatus insulators are better than those of porcelain insulators at the same site. The number of high pulses in the leakage current giving risk of a flashover, is much lower for silicone rubber insula-tors than for porcelain insulators. It can be shown that a large margin exists in the specific creepage distance of composite apparatus insulators in com-parison to porcelain insulators.

Total number of delivered appara-tus with composite insulators• Surge arresters 55 000• Circuit breakers 2 300• Instrument transformers 3 200

Service experienceSince 1985, when the first surge arresters with sili-cone sheds were installed, ABB has delivered a large number of high-voltage apparatus equipped with composite insulators. These have been installed in a wide range of environments ranging from marine to desert and/or areas with industrial pollution.

The performance of ABB insulators and prod-ucts in installations with extreme environmental conditions has been studied in detail. The observa-tions show excellent performance with insignificant changes in material properties.

The silicone material has proven its good per-formance at test stations in severe climates and at commercial installations all the world over.

Extensive testingComposite insulators with silicone rubber sheds have been subjected to extensive testing to ensure a high quality level and to verify the mechanical and electrical properties under all environmental condi-tions.

Testing is also performed at low ambient tem-peratures, down to -55 °C. The composite insulators comply fully with the requirements specified by IEC. The insulators have been subjected to vandal-ism tests where objects have been thrown at the in-sulators. A circuit breaker with polymeric insulators has even been subjected to gunfire to show that this kind of damage does not cause complete breakdown or explosions that may injure personnel or damage surrounding equipment.

Examples of performed tests• High and low temperature tests• Dielectric tests• UV radiation tests• Accelerated ageing tests• Mechanical strength tests• Over-pressure tests

�ABB

”By choosing ABB high voltage equipment with silicone rubber insulation, excellent performance and reliability can be assured for the lifetime of the equipment”.

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ABB ABHigh Voltage Products

SE-��1 80 LUDVIKA, SWEDEN

Tel: +��(0)��0 �8 �0 00

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E-mail: switchgear.solutions@se.abb.com

www.abb.com