The Electrical Insulation Characteristics for a HTS Cable Termination

Abstract

A research on several characteristics such as volume breakdown and surface discharge of insulators for a termination of power transmission class high temperature superconducting (HTS) cable was performed. In this paper, we investigated the surface discharge of glass fiber reinforced plastic (GFRP) in the air, nitrogen gas (GN 2 ) and cryogenic nitrogen gas (CGN 2 ) media. The breakdown characteristics of these media were also studied. Experimental results revealed that flashover voltage greatly depends on pressure, temperature, the kinds of insulating media and voltages. However, it is shallowly affected by shape and material of electrode. The breakdown voltage of liquid nitrogen (LN 2 ), GN 2 and CGN 2 deeply depends on the shape and dimension of electrode, kinds of voltages and pressure. Moreover, the breakdown voltage of CGN 2 and flashover voltage of GFRP in the CGN 2 is also influenced by temperature and vapor-mist density of the gas.Index Terms-Cryogenic insulation, HTS cable termination insulation, surface discharge, volume breakdown.

Comparative study of high voltage bushing designs suitable for apparatus containing cryogenic helium gas

“…Due to a leak in our mold the cast did not extend all the way up to the threads but stopped approximately 10 cm below (3). To even out the high electric field stress at the point at which the bushing bolted onto the main pressure cryostat we incorporated a squirrel cage arrangement made of copper (5). This part of the bushing was inside the cryostat, which experienced the high gaseous helium pressure and high temperature gradient from ambient temperature at the flange to 40-70 K at the lower end.…”

“…In one case they had transitioned from liquid nitrogen (77 K) to ambient by traversing through two gaseous chambers, one with cold gaseous nitrogen and the next, being SF 6 [4]. The other case was similar in construction where the transition was by going through two chambers with cold gaseous nitrogen and finally warm nitrogen [5]. Work that is of interest to us has been reported [6,7] at the Large Hadron Collider (LHC) in CERN and at the ATLAS project in CERN [8].…”

“…A liquid nitrogen jacket (4) reduced heat influx by radiation. The cryostat featured a 76 mm wide neck (5). The helium gas in the neck section is substantially warmer than in the main compartment of the cryostat due to heat influx through the main flange, port flanges and the bushing itself.…”

“…Bushing (1), high pressure gaseous helium inlet via heat exchanger (2), liquid helium inlet (3), liquid nitrogen inlet (4), and neck section of cryostat(5).…”

“…Photograph and drawing of Bushing B showing the aluminum conductor with brass cylinder (1), the epoxy body with sheds (2), the shortened top part due to vacuum problem (3), flange to pressure cryostat (4), field shaping insert (''squirrel cage'')(5), and the bottom sphere(6).…”