Investigation of the breakdown process of syntactic foam under lightning impulse stress at liquid nitrogen temperature

In superconducting components for electrical power distribution networks liquid nitrogen (LN₂) based insulation systems are commonly used. LN₂ has a cooling and an insulating function simultaneously. One disadvantage of these insulation systems is the bubble formation within LN2 due to heat losses of the current carrying conductor, which reduces the dielectric strength of the insulation system drastically. An alternative is a solid insulation system where LN₂ mainly takes a cooling function. This paper focuses on syntactic foam as a solid insulation system for superconducting power components. Syntactic foam is a composite material consisting of a polymeric matrix and embedded hollow microspheres. Both epoxy resin and unsaturated polyester resin serve as matrix material. The hollow microspheres´ sheath is made from glass or ceramic. Various syntactic foam compositions generated from the mentioned materials are investigated regarding their dielectric strengths under lightning impulse voltage stresses at liquid nitrogen temperatures (LNT). In addition to the experiments, numerical field simulations are carried out to understand the process of breakdown within syntactic foam.