Design research on the conductor of 10 kA class HTS DC power cable

High temperature superconducting (HTS) DC power cable shows a wide application prospect in the field of power transmission for its nearly lossless and rather high capacity. A 360 m/10 kA HTS DC power cable system, which connects the rectifier output of a substation with the bus bar of an electrolytic aluminium cell, will be put into operation at Henan Zhongfu Industrial Co., Ltd. As one of the items in this project, a 5 m/10 kA HTS DC power cable was developed, which is used to investigate the conductor design, fabrication, current-carrying capacity and stability of the 360 m/10 kA HTS power cable.The HTS DC power cable core consists of five conductor layers wound with spliced Bi-2223 wires with the length of 600 m. The cable core has five layers and 23 conductors in each layer with the outer diameter of 45.42 mm. The superconducting power cable is fabricated and tested. The critical current is about 14.3 kA at 77 K. The superconducting power cable is charged to 10 kA with rate of 10 A/s and operates at steady-state for 30 min.In this paper, the 10 kA HTS DC power cable design, fabrication and test are presented. The experimental research of the performance of spliced superconducting wire and charging, steady-state operating performance of the cable was carried out.     

An evaluation method for small-scale conduction cooled SMES cryogenic cooling system based on thermal analysis

The current flowing through a SMES is subjected to variations at a rate ranging from 0.1 A/s to 300 A/s under the influence of the power grid. The duration of power exchange varies from milliseconds to minutes, even to hours. When operating, the impact of AC losses in HTS tapes on the cryogenic cooling system should be considered. If the cryogenic cooling system fails to take away the generated heat effectively, this may lead to the temperature rise of the magnet and its possible damage. Therefore, it is essential to evaluate the technical and economical characteristic of cryogenic cooling system. Thus, a 5 MJ SMES model is built to calculate the temperature characteristic. A new factor δ is defined to assess the technological and economical validity of the chosen cryogenic scheme. The suitable capacity of the cryogenic cooling system is evaluated for different applications. The effect of the operating temperature on the technical and economical factor is also discussed.     

Cryogenic helium gas circulation system for advanced characterization of superconducting cables and other devices

A versatile cryogenic test bed, based on circulating cryogenic helium gas, has been designed, fabricated, and installed at the Florida State University Center for Advanced Power Systems (FSU-CAPS). The test bed is being used to understand the benefits of integrating the cryogenic systems of multiple superconducting power devices. The helium circulation system operates with four sets of cryocooler and heat exchanger combinations. The maximum operating pressure of the system is 2.1 MPa. The efficacy of helium circulation systems in cooling superconducting power devices is evaluated using a 30-m-long simulated superconducting cable in a flexible cryostat. Experiments were conducted at various mass flow rates and a variety of heat load profiles. A 1-D thermal model was developed to understand the effect of the gas flow parameters on the thermal gradients along the cable. Experimental results are in close agreement with the results from the thermal model.     

Operating characteristics of a single-stage Stirling cryocooler capable of providing 700 W cooling power at 77 K

High cooling capacity Stirling cryocooler generally has hundreds to thousands watts of cooling power at liquid nitrogen temperature. It is promising in boil-off gas (BOG) recondensation and high temperature superconducting (HTS) applications. A high cooling capacity Stirling cryocooler driven by a crank-rod mechanism was developed and studied systematically. The pressure and frequency characteristics of the cryocooler, the heat rejection from the ambient heat exchanger, and the cooling performance are studied under different charging pressure. Energy conversion and distribution in the cryocooler are analyzed theoretically. With an electric input power of 10.9 kW and a rotating speed of 1450 r/min of the motor, a cooling power of 700 W at 77 K and a relative Carnot efficiency of 18.2% of the cryocooler have been achieved in the present study, and the corresponding pressure ratio in the compression space reaches 2.46.     

Development and parametric study of the convection-type stationary adiabatic demagnetization refrigerator (ADR) for hydrogen re-condensation

The adiabatic demagnetization refrigerator (ADR) system in this paper is composed of a conduction-cooled current cycling high-temperature superconducting (HTS) magnet system, a magnetic bed assembly, its heat exchange parts and an auxiliary precooling stage (a commercial GM cryocooler and a liquid nitrogen vessel). The whole magnetic refrigeration system including the conduction-cooled HTS magnet is cooled by the precooling stage to absorb the rejection heat of the ADR cycle. The packed bed type magnetic bed consists of tiny irregular powders of Dy_0.9Gd_0.1Ni₂ enclosed in a thin walled stainless steel container (22.2 mm in O.D., 0.3 mm in thickness and 40.0 mm in height). The precooled heat transfer fluid (helium) travels through the magnetic material when heat rejection is required; otherwise the helium stagnates within its pores (pseudo-adiabatic process). Flow of the heat transfer fluid substitutes for the function of a traditional heat switch, creating, essentially, a forced-convection type heat switch. The magnetic bed assembly is periodically magnetized and demagnetized at the center of the conduction-cooled HTS magnet which can stably generate both strong and alternating magnetic field from 0 T to 3.0 T (0–130 A) with an average ramp rate of 0.24 T s⁻¹. The cooling capacities of the ADR system at 20 K which is the normal boiling point (NBP) of hydrogen, are 11.1 J cycle⁻¹, 6.3 J cycle⁻¹ and 1.9 J cycle⁻¹ when the temperature spans are 1 K, 2 K and 3 K, respectively. We describe the detailed construction of the ADR system and discuss the test results with the operational parameters (the entrained helium pressure, the mass flow rate of helium and the operating temperature span) in the 20 K region.     

Design and prototyping of a large capacity high frequency pulse tube

This document describes the design and the prototyping performed at CEA/SBT in partnership with AIR LIQUIDE of a high frequency large cooling power pulse tube. Driven at 58 Hz by a 7.5 kW flexure bearing pressure wave generator, this system provides a net heat lift of 210 W at 65 K. The phase shift is obtained by an inertance and a buffer volume. This type of cryogenic cooler can be used for on site gas liquefaction or drilling site and for high temperature superconductivity power device cooling (transmission lines, large generators, fault current limiters).In this paper, we focus on two essential points, the regenerator and the flow straightener. The regenerator is a key component for good performance of the pulse tube cooler. It must have a large thermal inertia, a low dead volume, a good heat transfer gas/matrix and at the same time, small pressure drop. In the present case and unlike typical moderate cooling power pulse tubes, the regenerator is very compact. However, the resulting conductive losses remain negligible compared to the cooling power targeted. The goal of the flow straightener is to avoid as much as possible any jet stream effect and to guarantee the uniformity of the velocity field at both ends of the pulse tube. Indeed multi-dimensional flow effects can significantly impact the performances of the machine.     

Parametric study for the cooling of high temperature superconductor (HTS) current leads

The analysis of cooling of a binary HTS 20 kA current lead (CL) operating between 4.5 and 300 K has been carried out. Assuming that the HTS module is conduction-cooled, two cooling options for the copper heat exchanger (HEX) part of the CL have been considered, i.e. (1) cooling with a single flow of gaseous helium and (2) cooling with two flows of gaseous helium. The ideal refrigerator power required to cool the whole HTS CL has been calculated for both cooling scenarios and different values of input parameters and the thermodynamic optimization has been performed for both cooling options. The obtained results indicate that the cooling Option 2 cannot provide significant savings of the refrigerator power, as compared to the Option 1. However, it has been observed that at the same helium inlet temperature the temperature at the warm end of the HTS part, and the resulting number of HTS tapes, can be reduced in the Option 2 with respect to the Option 1.     

Experimental study of the influence of cold heat exchanger geometry on the performance of a co-axial pulse tube cooler

Improving the performance of the pulse tube cooler is one of the important objectives of the current studies. Besides the phase shifters and regenerators, heat exchangers also play an important role in determining the system efficiency and cooling capacity. A series of experiments on a 10 W @ 77 K class co-axial type pulse tube cooler with different cold heat exchanger geometries are presented in this paper. The cold heat exchangers are made from a copper block with radial slots, cut through using electrical discharge machining. Different slot widths varying from 0.12 mm to 0.4 mm and different slot numbers varying from around 20–60 are investigated, while the length of cold heat exchangers are kept the same. The cold heat exchanger geometry is classified into three groups, namely, constant heat transfer area, constant porosity and constant slot width. The study reveals that a large channel width of 0.4 mm (about ten times the thermal penetration depth of helium gas at 77 K, 100 Hz and 3.5 MPa) shows poor performance, the other results show complicated interaction effects between slot width and slot number. These systematic comparison experiments provide a useful reference for selecting a cold heat exchanger geometry in a practical cooler.     

Investigation of two-phase heat transfer coefficients of argon–freon cryogenic mixed refrigerants

Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon–freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340 μm hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.     

Low cryogen inventory,forced flow Ne cooling system with room temperature compression stage and heat recuperation

We present design and commissioning results of a forced flow cooling system utilizing neon at 30 K. The cryogen is pumped through the system by a room-temperature compression stage. To decouple the cold zone from the compression stage a recuperating counterflow tube-in-tube heat exchanger is used. Commissioning demonstrated successful condensation of neon and transfer of up to 30 W cooling power to the load at 30 K using only 30 g of the cryogen circulating in the system at pressures below 170 kPa.     

Design and experimental investigation of a cryogenic system for environmental test applications

This paper is concerned with the design, development and performance testing of a cryogenic system for use in high cooling power instruments for ground-based environmental testing. The system provides a powerful tool for a combined environmental test that consists of high pressure and cryogenic temperatures. Typical cryogenic conditions are liquid hydrogen (LH2) and liquid oxygen (LO2), which are used in many fields. The cooling energy of liquid nitrogen (LN2) and liquid helium (LHe) is transferred to the specimen by a closed loop of helium cycle. In order to minimize the consumption of the LHe, the optimal design of heat recovery exchangers has been used in the system. The behavior of the system is discussed based on experimental data of temperature and pressure. The results show that the temperature range from room temperature to LN2 temperature can be achieved by using LN2, the pressurization process is stable and the high test pressure is maintained. Lower temperatures, below 77 K, can also be obtained with LHe cooling, the typical cooling time is 40 min from 90 K to 22 K. Stable temperatures of 22 K at the inlet of the specimen have been observed, and the system in this work can deliver to the load a cooling power of several hundred watts at a pressure of 0.58 MPa.     

Wrapped multilayer insulation design and testing

New vehicles need improved cryogenic propellant storage and transfer capabilities for long duration missions. Multilayer insulation (MLI) for cryogenic propellant feedlines is much less effective than MLI tank insulation, with heat leak into spiral wrapped MLI on pipes 3–10 times higher than conventional tank MLI. Better insulation for cryogenic feed lines is an important enabling technology that could help NASA reach cryogenic propellant storage and transfer requirements. Improved insulation for Ground Support Equipment could reduce cryogen losses during launch vehicle loading. Wrapped-MLI (WMLI) is a high performance multilayer insulation using innovative discrete spacer technology specifically designed for cryogenic transfer lines and Vacuum Jacketed Pipe (VJP) to reduce heat flux.The poor performance of traditional MLI wrapped on feed lines is due in part to compression of the MLI layers, with increased interlayer contact and heat conduction. WMLI uses discrete spacers that maintain precise layer spacing, with a unique design to reduce heat leak. A Triple Orthogonal Disk spacer was engineered to minimize contact area/length ratio and reduce solid heat conduction for use in concentric MLI configurations.A new insulation, WMLI, was developed and tested. Novel polymer spacers were designed, analyzed and fabricated; different installation techniques were examined; and rapid prototype nested shell components to speed installation on real world piping were designed and tested. Prototypes were installed on tubing set test fixtures and heat flux measured via calorimetry. WMLI offered superior performance to traditional MLI installed on cryogenic pipe, with 2.2 W/m² heat flux compared to 26.6 W/m² for traditional spiral wrapped MLI (5 layers, 77–295 K). WMLI as inner insulation in VJP can offer heat leaks as low as 0.09 W/m, compared to industry standard products with 0.31 W/m. WMLI could enable improved spacecraft cryogenic feedlines and industrial hot/cold transfer lines.     

The characterization of a cascade thermoelectric cooler in a cryosurgery device

An experimental investigation using a Peltier thermoelectric cooler (TEC) to cool down a cryoprobe for cryosurgery was performed. Two prototypes of cryosurgery devices consisting of 5- and 6-stage TEC modules were analyzed using a variety of electrical voltages, circulating thermostatic bath (CTB) temperatures, and heat exchanger configurations to obtain an optimum cold side temperature and temperature differences between sides of the modules. To increase the heat exchanges at the hot side, a heat pipe system with a water block was used. Using an electric voltage of 12 V and a CTB temperature of 273.55 K, a cryogenic temperature of 177.09 K and a temperature difference of 99.87 K were achieved. These results indicate that the TEC module can be an effective cooling source for cryosurgery. The prototype has shown potential for clinical trials.     

Cryogenic design and test results of 30-m flexible hybrid energy transfer line with liquid hydrogen and superconducting MgB2 cable

In this paper we present the development of a new hybrid energy transfer line with 30 m length. The line is essentially a flexible 30 m hydrogen cryostat that has three sections with different types of thermal insulation in each section: simple vacuum superinsulation, vacuum superinsulation with liquid nitrogen precooling and active evaporating cryostatting (AEC) system. We performed thermo-hydraulic tests of the cryostat to compare three thermo-insulating methods. The tests were made at temperatures from 20 to 26 K, hydrogen flow from 70 to 450 g/s and pressure from 0.25 to 0.5 MPa. It was found that AEC thermal insulation was the most effective in reducing heat transfer from room temperature to liquid hydrogen in ∼10 m section of the cryostat, indicating that it can be used for long superconducting power cables. High voltage current leads were developed as well. The current leads and superconducting MgB₂ cable passed high voltage DC test up to 50 kV DC. Critical current of the cable at ∼21 K was 3500 A. It means that the 30 m hybrid energy system developed is able to deliver ∼50–60 MW of chemical power and ∼50–75 MW of electrical power, i.e. up to ∼135 MW in total.     

Novel compact sorption generators for car air conditioning

A prototype compact generator using the activated carbon–ammonia pair based on the plate heat exchanger concept has been designed and built at Warwick University. The novel generator has low thermal mass and good heat transfer. The heat exchanger uses nickel-brazed shims and spacers to create adsorbent layers only 4 mm thick between pairs of liquid flow channels of very low thermal mass. The prototype sorption generator manufactured was evaluated under EU car air conditioning test conditions.The prototype sorption generator is described and its experimental performance reported. While driven with waste heat from the engine coolant water (at 90 °C), a pair of the current prototype generators (loaded with about 1 kg of activated carbon) operating out of phase has produced an average cooling power 1.6 kW with about 2 kW peaks. The typical average COP obtained is 0.22.     

A cryogenic DAC operating down to 4.2 K

This paper presents a 10 bit CMOS current steering digital to analog converter (DAC) that operates from room temperature to as low as 4.2 K. It works as the core part of a cryogenic Silicon quantum computer controller circuit producing rapid control gate voltage pulses for quantum bits (qubits) initialization. An improved analog calibration method with a unique unit current cell design is included in the D/A converter structure to overcome the extended cryogenic nonlinear and mismatch effects. The DAC retains its 10 bit linear monotonic behavior over the wide temperature range and it drives a 50 Ω load to 516 mV with a full scale rise time of 10 ns. The differential non-linearity (DNL) of the converter is 0.35LSB while its average power consumption is 32.18 mW from a 3 V power supply. The complete converter is fabricated using a commercial 0.5 μm 1 poly 3 metal Silicon on Sapphire (SOS) CMOS process.     

Cryogenic flat-panel gas-gap heat switch

A compact additive manufactured flat-panel gas-gap heat switch operating at cryogenic temperature is reported in this paper. A guarded-hot-plate apparatus has been developed to measure the thermal conductance of the heat switch with the heat sink temperature in the range of 100–180 K. The apparatus is cooled by a two-stage GM cooler and the temperature is controlled with a heater and a braided copper wire connection. A thermal guard is mounted on the hot side of the device to confine the heat flow axially through the sample. A gas handling system allows testing the device with different gas pressures in the heat switch. Experiments are performed at various heat sink temperatures, by varying gas pressure in the gas-gap and with helium, hydrogen and nitrogen gas. The measured off-conductance with a heat sink temperature of 115 K and the hot plate at 120 K is 0.134 W/K, the on-conductance with helium and hydrogen gases at the same temperatures is 4.80 W/K and 4.71 W/K, respectively. This results in an on/off conductance ratio of 37 ± 7 and 35 ± 6 for helium and hydrogen respectively. The experimental results matches fairly well with the predicted heat conductance at cryogenic temperatures.     

Development of mechanical cryocoolers for the Japanese IR space telescope SPICA

The next Japanese infrared space telescope SPICA features a large 3.5-m-diameter primary mirror and an optical bench cooled to 4.5 K with advanced mechanical cryocoolers and effective radiant cooling instead of using a massive and short-lived cryogen system. To obtain a sufficient thermal design margin for the cryogenic system, cryocoolers for 20 K, 4 K, and 1 K have been modified for higher reliability and higher cooling power. The latest results show that all mechanical cryocoolers achieve sufficient cooling capacity for the cooling requirement of the telescope and detectors on the optical bench at the beginning of life. Consequently, the feasibility of the SPICA cryogenic system concept was validated, while attempts to achieve higher reliability, higher cooling capacity and less vibration have continued for stable operations at the end of life.