Electric Field Investigations of a Compact Superconducting Three-Phase Single Conductor Cable Assembly

A new compact cable design was investigated using only liquid nitrogen (LN2), general used as coolant of superconductors, as sole electric insulation. First, it was analyzed which conductor arrangement is better suited in terms of maximum electric field strength to withstand the applied voltage of 123 kV. It was found that a three-phase single conductor arrangement with a maximum electric field strength of 10.5 kV/mm is more suitable than a triaxial arrangement with a maximum field strength of 16.5 kV/mm. Furthermore, a corresponding supporting insulator was developed to provide the highest possible mechanical and electrical withstand. A major focus was on selecting the most appropriate material and its permittivity in combination with the surrounding LN2 (ϵr = 1.43) to reduce the electric field strength to its possible minimum. The best relative permittivity for the supporting insulator is in the range between 1.4 and 3.4.