Variable pressure and temperature liquid nitrogen cryostat for optical measurements with applied electric fields

Abstract

A cryostat with a high-voltage bushing, optical observation ports, variable controlled temperature and pressure has been designed to further the study of liquid nitrogen as a dielectric medium. The novelty in this design lies in the simultaneous achievement of these functions in a single design with a sufficiently large vessel to accommodate realistic geometries for high temperature superconducting power cable termination prototypes. In addition, a commercial single-stage helium expander cryo-cooler is integrated into the apparatus to achieve steady state temperatures down to 63.5 K, without the need for sacrificial loss of liquid nitrogen to maintain vessel temperature. The cryostat inner vessel is certified for operating pressures up to 2 MPa. A custom-made filled-resin bushing provides an electrical feed-through rated to 76.2 kV ac. For optical measurements with a range of sample geometries four optical ports are incorporated into the vessel utilizing sapphire windows and indium seals to form the inner pressure vessel. A technique employing a copper-vapour laser light source and high-speed digital camera for stroboscopic image capture of density change streamers and bubble dynamics with synchronized collection of electrical discharge data has been developed. This design has been used to study pre-breakdown phenomena, bubble dynamics with applied electric fields and electrical breakdown. General construction, mode of operation and initial results are presented.

The feasibility of using UHF sensors to measure partial discharges in liquid nitrogen

“…The high voltage bushing of the cryostat was designed and tested to be PD free up to 50kV AC [2]. A 50 Hz sinusoidal high voltage was applied via a transformer with variable output (0-50kV).…”

“…The experiments utilise point to plane electrode configuration located inside a cryostat with high voltage bushing rated to 50kV PD free [2]. The sensor is mounted on the outside wall of the cryostat with uses of dielectric windows and signals are captured by a digital oscilloscope with a bandwidth of 2.5GHz.…”

Cryogenic dielectrics and hts power apparatus: research at the university of southampton

“…To study the development of streamers a technique to synchronously record electric discharge signals with imaging of streamers using a high-speed digital camera has been developed [8]. Using a pointplane sample with composite LN2 and solid dielectric, streamers are initiated from a tungsten needle for three solid barrier materials, including a glass fibre reinforced resin (10G/40), a cotton fibre reinforced resin and polytetrafluroethyline (PTFE) [6,8,9].…”

Design and Test of Cryogenic Cold Plate for Thermal-Vacuum Testing of Space Components

“…Therefore, there is a significant interest in testing space components in vacuum, vibrating, and cryogenic conditions. Cryostats and cold plates for thermal and vacuum conditions have been widely developed by companies and research teams [10][11][12][13][14]. However, the design of equipment for carrying out vacuum, cryogenic, and vibration tests simultaneously is not well developed.…”