The authors have carried out a series of tests on extruded ethylene-propylene rubber (EPR) insulated low temperature superconducting power cables. This paper focuses on tanδ, a dielectric dissipation factor, of EPR insulation in the form of cable configuration at cryogenic temperatures. The problem of electric contact between EPR insulation and a measuring electrode was solved by adopting SZ wire shielding, which enabled us to obtain reliable data even in the cryogenic temperature region. Although it is reported that a film sample gives fairly high tanδ at the liquid helium temperature, the cable samples used in this study showed very stable tanδ, as low as in the area of 10-4. The estimated dielectric loss of the cable was comparable with the AC loss of superconductors.
