Yury Ivanov

Double Peltier Current Lead for Heat Leak Reduction at the Terminals for Superconducting Direct Current Applications

For superconducting direct current applications, heat leak reduction at the terminal is a key issue for high performance systems and especially for small ones such as the distribution in internet data centers. We propose a double Peltier current lead (PCL), where the suitable combination of two Peltier modules can enhance the performance of PCL. Using the model parameters of actual thermoelectric materials, we estimated the heat leak on PCL using a thermal balance equation. At the double PCL, the large temperature difference on the current lead can be split to two thermoelectric materials and then the performance of PCL can be enhanced. As each of the thermoelectric materials has better working temperature range, an optimized combination of shape factors can be used for the high performance current lead at the terminals for superconducting application systems.

Current Imbalance and AC Losses of Long-Distance DC HTS Cable

Despite intensive research in the field of applied superconductivity only now we start to use of this phenomenon for the most obvious application, namely, power transmission. At present, it can be seen an explicit shift from AC to DC HTS cable systems due to the many advantages of the DC ones. However, even at constant current transmission line is subjected to current fluctuations and, consequently, AC losses. One more reason for reducing the efficiency of HTS lines is current imbalance. It is associated with the presence of electrical resistance at the soldered connections of the superconducting tapes. Although these resistances are very low, but against the background of zero resistance of the rest of the superconductor they determine the individual currents in tapes and introduce essential nonlinearity into the dependence of these currents on the total current. In order to estimate AC losses the frequency characteristics of the ripple current were calculated taking into account current imbalance in the cable.

The experiments of 200-meter superconducting DC power cable in Chubu university and the estimation for longer cable cooling

After the 200-meter superconducting DC power cable experimental facility had been completed in spring of 2010, three experiments have been done until March, 2011. We adapt the straight pipe for the inner cryogenic pipe to reduce the heat leak and the pressure drop of liquid nitrogen circulation because the surface area is minimized for the straight pipe, and the terminal cryostats of the cable ends are movable to absorb the shrinkage of the cable in the cooling-down phase and the expansion in warming-up phase to reduce the tensile strain of the high temperature superconductor tape. We also continue the Peltier current lead experiment to reduce the heat leak at the terminal. We performed several kinds of the experiments to obtain the basic data for a long cable system. We changed and improved the experimental devices during the experiments. The pressure drop of the liquid nitrogen circulation was around 1 kPa for the flow rate of 10 L/min in the experiment. We summarized the experimental results briefly, a...

Cooling test of the 500 m class superconducting DC power transmission system

Recently, 500 m and 1000 m class superconducting DC power transmission systems were constructed in the Ishikari area in Japan and the cooling test of the 500 m system was performed. The heat leak of the cryogenic pipe and the total heat load of the system were estimated in the cooling test. The cryogenic pipe of the system has two inner pipes in one outer pipe for circulation. The heat leak was 0.98 W/m and 0.44 W/m for each inner pipe. The total heat load of the system was 1.37 kW except for the heat load by the current feeding and the circulation pumps, while the total cooling power of the system was approximately 3 kW. The pressure drop of the circulation was measured to be 19.5 kPa at the rated flow rate of 30 L/min for the 1000 m circulation both ways in the 500 m transmission line. By the cooling test, it was confirmed that the system can be operated stably.

Circulation Test of Liquid Nitrogen for Long Superconducting DC Power Transmission Lines

The pressure drop during circulation of the refrigerant limits the distance for superconducting power transmission. Evaluation of the pressure drop with respect to the flow rate of the refrigerant is crucial, particularly for long transmission lines. A circulation test, including pressure drop measurements, was performed in the sixth cooling test with the 200-m-class superconducting dc power transmission system at Chubu University (CASER-2). Pressure drops were measured in the high-flow-rate region, up to 31 L/min, to simulate 1-km-class systems, unlike those used in the first five cooling tests. A pressure drop of 12 kPa at 31 L/min for the 200-m cryogenic pipe was obtained. The obtained results were compared with the calculated results and showed good agreement. The model used for the calculation can predict the pressure drop with sufficient accuracy, making the prediction for the pressure drop for long transmission lines possible.

Thermosiphon Effect During Cooling Test of a 200 m DC HTS Cable Facility

Industrial application of HTS cables for power transmission is largely constrained by the imperfection of the cryogenic pumps that are expensive apparatuses providing additional heat load. Temperature and, consequently, density of the liquid cryogen change while it flows through the channel. If the cryogenic pipe route has enough elevation difference, this will lead to natural circulation. As a result, it may be not necessary to use pump, and the system cost and complexity will reduce significantly. The feasibility of the given approach was confirmed theoretically for various system configurations. Preliminary experiments were also carried out using 200-m dc HTS facility at Chubu University during the third and fourth cooling tests. Recently, during the sixth cooling test, the cryogenic pump was stopped intentionally. Meanwhile, the natural circulation of the liquid nitrogen was observed at flow rate of about 2 l/min, and the cable temperature remained low.

Construction and the Circulation Test of the 500-m and 1000-m DC Superconducting Power Cables in Ishikari

A demonstration project of the dc superconducting power transmission line using the BSCCO wires was started in Ishikari, Japan as a national project (Ishikari project) from 2013FY. In the project, two power lines have been installed. Line 1 connects a photovoltaic power plant and an Internet data center by a 500-m underground cable for practical use, whereas line 2 with a 1000-m cable will be used for verification tests. In this project, we developed a new design of an adiabatic double tube with reduced heat leaks, i.e., <;1.5 W/m. We have also adopted the Peltier current lead that drastically cuts heat transfer at the cable terminal below 35 W/kA. To control the thermal contraction and expansion of the cable to avoid its breakage, we adopted two techniques, namely, a movable cryostat and a helical deformation technique. The construction was started in the field in June 2014 and completed at the end of April 2015 for line 1. Then, we performed the first cooling test for line 1 from May to June in 2015, during which we have confirmed that the thermal performance is as good as what we designed, and the current of 5 kA was successfully transported.

Thermoelectric Property Dependence on Performance of Peltier Current Leads Under Overcurrent Conditions

Superconductivity can potentially provide a solution to the world’s energy needs because superconducting transmission and distribution (T&D) systems can decrease losses and are also capable of integrating renewables into the power grid. At Chubu University we have built a 200-m-class superconducting direct-current T&D system (CASER-2). To minimize heat leakage from the current leads, we investigated thermoelectric materials. The Peltier current lead (PCL) is one of the key technologies that will enhance the performance of superconducting systems: as direct current (DC) flows through the current lead, thermoelectric elements on opposite terminations of the superconducting line can be used to decrease the heat ingress to the cryogenic environment (n-type on one end, p-type on the opposite end). The heat leakage to the cryogenic environment depends on the properties of the thermoelectric materials. In this paper, we estimate the performance of PCLs in cryogenic operations, including the potential for overcurrent operation, through both modeling and experiments at CASER-2.

Heat leak and pressure drop measurements of the 1000 m class superconducting DC power transmission system in Ishikari

500 m class and 1000 m class superconducting DC power transmission systems were constructed in Ishikari, Japan (Ishikari project). The 500 m system connects a photovoltaic power plant to an internet data center. On the other hand, the 1000 m system has been used to obtain data for construction of future longer transmission lines. In the summer of 2016, the second cooling and circulation test of the 1000 m system was performed, which was followed by the first cooling test performed in the winter of 2015. In these tests, characteristics of the cryogenic system, including a heat leak and a pressure drop, were measured. The heat leak of the system was estimated from the temperature rise and the flow rate of the liquid nitrogen. The measured values were 1.746kW and 2.091kW at the outer pipe temperature of -2.4°C and 17.4°C, respectively, for the cable including the terminals. The pressure drops were measured with pressure gauges for the liquid nitrogen. The pressure drop at 36.03L/min was 42.80kPa for the circulation distance of 2000m. This work was supported in part by the Japanese Ministry of Economy, Trade and Industry (METI) and by the New Energy and Industrial Technology Development Organization (NEDO).

Ferromagnetic Coating for Decreasingof Self-Magnetic Field Acting on HTS Tapes

The decreasing of critical current in the high-temperature tape superconductor (HTS) can be prevented by decreasing of the perpendicular component of self-magnetic field. The coating of this tape by the ferromagnetic material can deform the magnetic field around the HTS tape with flowing transport current. The present report contains the finite-element analysis of the effect of ferromagnetic coating near the HTS tape. The optimal configuration of the ferromagnetic coating for minimizing the perpendicular component of magnetic field was found. In present case, it reduces from 0.04 T to less than 0.01 T. The optimal shape of the coating contains the gap along the lateral side of the HTS tape. The influence of the twisting of the tape coated by ferromagnetic was also investigated. It was found that the difference between twisted and nontwisted cables was not large. The study was also performed for the stack of HTS tapes where neighbor tapes have the opposite direction of the transport current. It was found that the ferromagnetic coating and ribs make the magnetic field near edges smooth.