A capacitance-graded cryogenic high voltage bushing for vertical or horizontal mounting

The cryogenic high voltage bushing for the terminations of the 138 kV, 4100 A superconducting cable prototype at the Brookhaven National Laboratory (BNL) is described. The bushing is energized with the line-to-ground voltage between the coaxial centre and outer surrounding conductors, in the axial direction there is a temperature difference from ambient to about 6 K.The capacitively graded bushing can be mounted in any position. It is vacuum tight and withstands pressures of more than 20 bar. The heat leak of the insulation body in axial direction is only 8.5 W.The electrical specifications of the bushing are: 825 kV, 1.2 × 50 μs impulse voltage; 240 kV rms ac 2h test voltage: and > 160 kVs partial discharge inception voltage.This bushing concept may easily be modified to meet most conceivable thermal, mechanical and electrical requirements of cryogenic high voltage engineering.