Silicone gel

Silicone gels are relatively new insulating materials compared to the classic dielectrics used in high and medium voltage technology, such as cast resin, polyethylene or oil. They belong to the group of cold-vulcanizing two-component silicone elastomers and differ in their material structure from the silicone rubbers increasingly used in the field of composite insulators and cable accessories in particular due to a considerably lower cross-linking density and a typically high proportion of non-cross-linked components.
The important properties of silicone gels from a high and medium voltage point of view are their high electrical strength, good thermal stability, a high degree of elasticity and their pronounced inherent adhesiveness, which promises considerable advantages over other insulating materials, especially in the area of electrically highly stressed interfaces.
Currently, silicone gels are mainly used as potting compounds for electronic components, e.g. in automotive and power electronics. They are mostly used because of their good mechanical and thermal properties and to protect the components used against corrosion. One application in which the gels are exposed to significantly higher field strengths is currently used as a potting compound in high-performance semiconductor modules (IGBT), for example.
In energy technology, silicone gel has so far been used in the field of low-voltage connection technology. In particular, the good compatibility of silicone elastomers with all common insulation materials, their wide application temperature range (-40°C to 90°C) and their anti-corrosive effect are utilized. The positive experience gained in low-voltage technology also makes silicone gels appear interesting for use in high- and medium-voltage technology. However, an application in this area requires very precise knowledge of the relevant material properties as well as extensive knowledge of their dependencies on the influencing factors to be expected in the respective area of application.

Against this background, the dielectric properties - in particular the electrical strength - of various silicone gels are to be investigated as a function of the parameters that are important for high and medium voltage insulation and connection technology as part of this research project. In addition to the behavior under short-term electrical load, the electrical and thermal aging behavior is an essential part of the investigations.
Based on the results obtained, the material silicone gel is to be characterized, evaluated and optimized with regard to its use in individual applications. The limitations of the material will be identified and guidelines for the design and construction of high and medium voltage insulation will be developed. In addition to the question of long-term behaviour and thus reliability as an insulating material, which is particularly important for use in electrical power engineering equipment, one focus is on the investigation and optimization of its interface properties.
Our department has a materials laboratory and various laboratories for high-voltage testing to carry out research work. In addition to well-known companies in the field of electrical power engineering, Wacker Chemie AG, Europe's largest manufacturer of silicones, is working closely with the department as a partner and sponsor in this project.

Building on the silicone gel work, the Department of Systems and High Voltage Technology is researching a further step in the modification of insulating materials. The aim is to develop and investigate field-controlling gels. This type of insulating material has a highly non-linear property with regard to electrical conductivity. In the conventional field strength range, the material behaves like a high-quality insulator. Above a certain field strength, however, this behavior changes to a very conductive range.

This property reduces areas of high field strength in the insulating material, which can lead to partial discharges and ultimately to degradation and destruction of the insulation. The insulating material adjusts its own conductivity in such a way that voltage control is achieved, which until now could only be achieved with complex additional components and a very careful design. In the project described below, this material is to be further developed and qualified for use in an industrial product.