Sven Schumann

Investigation of mechanical properties of silicone syntactic foam for outdoor applications

Silicones are especially suitable as insulation materials in outdoor applications and state of the art as coating and shed materials. However, composite insulators can still be improved with regard to weight and cost reduction by adding cost-efficient, light weight filling materials. In this work hollow microspheres (HMS) are applied, which influence a broad range of material properties such as mechanical properties. Therefore, investigations regarding mechanical properties (tear and tensile strength, elongation at break) of the resulting composite material are performed to identify suitable material compositions.

Investigation of hydrophobicity transfer and recovery of silicone syntactic foam for outdoor applications

Filling cost-intensive silicone with cost-efficient, light weight filling materials can improve weight and costs of silicone composite insulators. This next step to improving composite insulators can be achieved by adding filling materials like hollow micro spheres (HMS). Good hydrophobicity properties are highly important to ensure long lifetime of polymer outdoor insulators. It is known that fillers influence the hydrophobicity of silicone. Hence, dynamic hydrophobicity properties of silicone syntactic foam have to be examined since low-density fillers have not been applied yet in outdoor insulation materials. The goal is to ensure long term hydrophobicity of the newly developed silicone syntactic foam and to identify suitable material compositions.

Thermal behavior and resistance against electrical discharges of modified silicones for outdoor application

Silicone composite insulators are state of the art for outdoor applications. The development of these insulators has reached a high level so in a next step the weight of these insulators can be reduced. One way to do so is by adding a low-density filling material. In this paper, the thermal stability of silicones filled with hollow microspheres (HMS) with diameter in the micrometer range is examined. High thermal stability is a key property of outdoor insulation materials as it determines the resistance against arc discharges as well as erosion due to dry band discharges. Therefore, arc resistance tests, inclined plane tests and thermogravimetric analysis are used to investigate the influence of HMS on thermal stability of silicone. The influences of thermal material properties like heat conductivity, heat capacity and temperature conductivity are examined and a method to calculate heat conductivity of porous composite materials is discussed. Results show no influence of thermal material properties on thermal stability, thus observed decrease of thermal stability of silicone filled with glass HMS cannot be explained by thermal characteristics. Instead, increase of surface area of the silicone is identified as key parameter, which causes a stronger thermal degradation. In addition, application of glass HMS in liquid silicone rubber (VMQ1) hinders the curing and reduces thermal stability further. Adding of ceramic HMS and silanization of glass HMS decreases erosion and increases arc resistance. This can be explained by an increased interphase quality between the silicone and these fillers, which prevent accelerated thermal degradation due to an increased thermally active surface area of the silicone.

Influence of water absorption and chemical degradation on dielectric properties of silicone syntactic foam

A promising next step to improve silicone composite insulators is to add cost-efficient, light-weight filling materials to the cost-intensive silicone. Therefore, in our research, hollow micro spheres (HMS) are used to create syntactic foam (Figure 1). Syntactic foam has already been investigated for high voltage indoor applications, based on epoxy resin and silicone gel [1-3]. Hence, the knowledge regarding the ageing behavior of syntactic foam for outdoor applications is still incomplete yet. The goal of the development of silicone based syntactic foam for outdoor applications is to ensure comparable outdoor performance to commercially used materials nowadays at lower costs. Among other material properties [4-7], water absorption and ageing effects of chemical and physical degradation due to water have to be considered to ensure long lifetime for outdoor insulation materials [8]. The suggested test methods according to IEC TR 62039 are the 100 h boiling test according to IEC 62217 with subsequent electric breakdown examination and loss factor measurements after long-term water immersion for 50 days at 50 °C [9]. The loss factor should not exceed 0.2 after water storage to fulfill the requirements for outdoor applications [8].