The complex permittivity of epoxy based nanocomposites with alumina and magnesium oxide fillers at very low temperatures

Delivery of energy in areas with a large population density and little space for high voltage equipment is an issue for utility companies in metropolises. Gas insulated switchgear is an alternative to conventional cable systems, enabling higher energy densities. However, the sulfur hexafluoride used in GIS causes environmental problems, which may not be acceptable anymore in a society with emphasis on sustainability. An alternative to this are superconducting cables. High temperature superconducting cables operate at temperatures close to the boiling point of nitrogen, which is 77 K. Not much is known about the dielectric behavior of insulating polymers at such temperatures. This exploratory work investigates how the complex permittivity of epoxy based nanocomposites changes at very low temperatures. A broadband dielectric spectrometer was utilized to acquire the real and imaginary part of the complex permittivity, along with the loss factor. The base polymer for all samples is a commercially available bisphenol-A epoxy with anhydrite hardener. As filler material magnesium oxide powder was used with an average particle size of 22 nm and alumina filler with 50 nm average diameter. Both particle types were modified with a silane coupling agent, in order to achieve a uniform dispersion of particles in the host material. Neat epoxy samples were used as a reference.