E & E / Electrical Insulators (incl HV)

Electrical Insulators (incl HV)

An electrical insulator is part of an assembly (cable) to facilitate the transmission of power or signals. The insulator helps ensure optimal transmission (minimal loss of power and signal) and protection against the environment. They are non-conductive (electrons within the insulating material will not flow freely under the influence of an electric field) – this is often referred to as the material having a high dielectric strength.

The term insulator is also used to describe the insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers. They support the weight of the suspended wires without allowing the current to flow through the tower to ground. Different materials may be used like Ceramics, Glass, Epoxy Resin or Silicon Rubber.

For epoxy based low and medium voltage insulators Sibelco’s mineral fillers bring the following characteristics:

  • Mechanical strength (Silica and Wollastonite)
  • Thermal conductivity (Silica)
  • High fill level possible (Silica)
  • Economical (Silica)

For Silicone based high voltage insulators Sibelco’s mineral fillers bring following characteristcs

  • Improved arc resistance (ATH)
  • Good and constant electrical resistivity (ATH)
  • Improved erosion resistance (ATH)
  • Economical (ATH)


Low and Medium Voltage Insulators

Insulators used for low and medium voltage can be made from various materials like glass, ceramics or composite polymer materials. While polymeric materials insulate electricity very well, they also insulate the heat which is built up under electrical load. Glass and ceramics deal with this heat buildup much better. To improve the thermal conductivity, Epoxy based composite systems are often filled with high amounts of very pure finely ground Quartz flour. 

High voltage insulators

Insulators used for high voltage power transmission can be made from glass, ceramics or composite polymer materials. Ceramic insulators are made from clay, quartz or alumina and feldspar, and are covered with a smooth glaze to shed water. Insulators made from glass have better electrical properties, but attract condensation and dirt more easily. 

Since the 90’s, composite polymeric insulators have steadily grown to be leading in several segments. For example for high voltage applications, over 90% of the new insulators produced are made from Silicon Rubber covered fibreglass rods. EPDM is also used in some cases, but silicone rubber is preferred due to its excellent hydrophobicity and the ability to transfer hydrophobicity to dirt on the surface of the insulator, thereby maintaining arc-resistance. This makes silicone an ideal material for insulators servicing polluted areas. 

For all types of insulators and as a leading supplier to the ceramics & glass industry, Sibelco offers an array of highly pure and finely ground minerals. Building on these relations, following markets in the newer polymeric materials, we also offer very fine ground quartz flour or ATH for low and medium voltage epoxy resin insulators.

In the high voltage segment, among the newer insulating materials used, insulation silicone rubber has received the most attention. However, pure silicone rubber shows little tracking and erosion resistance. So, some properties of silicone rubber need to be improved to extend service life. The fillers are added to the polymer to promote specific properties and also to reduce costs.