high-Tc Superconducting Power Research Articles

Experimental Analysis of Thermally and Magnetically Triggered Switch for High-Tc Superconducting Power Converting System

In this paper, characteristics of a thermally and magnetically triggered switch for a high-Tc superconducting (HTS) power converting system are experimentally analyzed. For verifying the efficiency of the suggested switch, current charging and discharging tests using heater-triggered switch with or without an external magnetic field are performed. Charging tests are performed with two charging sequences, i.e., CS1 and CS2. Each sequence is experimented with two kinds of heater currents to maintain different temperatures. Saturation current and saturation time are detected to calculate the pumping rate. Two discharging sequences, i.e., DS1 and DS2, are used for discharging tests with heater current to maintain 120 K. From the results, normalized load energies are calculated and compared.

Design and Test of HTS Power Converting System With Multiple Magnets Considering Various Sequential Controls of Heater-Triggered Switches

This paper presents experimental results of the designed high-Tc superconducting (HTS) power converting system with multiple GdBCO magnets. The system is tested by various sequential controls of four heater-triggered switches and an electromagnet, which consists of two energy storage magnets (ESMs). The experiments are mainly composed of two modes. The first one is a simultaneously operating mode (Mode1), and another is an alternative operating mode (Mode2). Each two sequences are performed at Mode1 (CS1 and CS2) and Mode2 (CS3 and CS4) for charging the ESMs, respectively. In those experiments, the average pumping rate of each sequence is calculated at about 17.55, 41.26, 10.25, and 25.83 mA/s, respectively. In the discharging test, two sequences are tested. Load energy is calculated from load voltage and current due to the difference between precharged energy to verify which operating mode is more effective. Load energy of each sequence reached about 47.97 and 38.83 J after 2000 s, respectively.

Analysis of a High-Tc Superconducting Power Converting System

This paper presents the analysis of a high-Tc superconducting (HTS) power converting system, as well as its operational characteristics. The converting system can be used to charge and discharge a magnet made of series-connected pancake coils. The HTS converting system consists of two heaters, a primary copper winding, a secondary HTS winding, a series-connected HTS pancake coil, an iron core and a conventional copper load. In the experiments, the charging and discharging periods were 7.5 and 2 s, respectively. A partial region of the superconducting tape in a secondary HTS winding is switched to a normal region by a buried heating coil. To measure the converting-current with respect to the magnet flux changes, a hall sensor was installed at the center of the pancake coil. In this experiment, the charging-current and discharging-energy reached about 51.7 A and 36.8 J, respectively. The experimental results have been compared with theoretical predictions by using the finite difference method.

Qualification Test of a 80 kV 500 MW HTS DC Cable for Applying Into Real Grid

Until now, some countries including South Korea have made considerable progress in the development of HTS (High Tc Superconducting) power equipment. Superconducting power cable systems are the strongest candidate from the viewpoint of their use in the real grid owing to their high current capacity. Specially, in the future, high-current long-distance HTS DC cables will play an important role in power transmission systems because, in contrast to HTS AC cables, HTS DC cables experience nearly no loss. In this paper, the authors suggest a new testing method for the load cycle and suitable thermal cycles to meet the requirements for HTS DC cables to be applied to the real grid. A prototype 100 m/3.25 kA/80 kV HTS DC cable system was developed for the qualification test in South Korea. The qualification test was carried out, based on HTS experience, the international standard for HTS AC cables, and the standards for conventional HVDC cables. It was performed in the same manner as that for a conventional HVDC cable for 6 months in the KEPCO PT (Power Testing) Center. Since its successful qualification test, the 500 MW/80 kV HTS HVDC cable system will have been operated in the KEPCO real grid since 2015, to evaluate its practical requirements and confirm its technical feasibility. This paper presents the recommendations and results of the qualification test for HTS DC cables.

Design and Test of a High-Tc Superconducting Power Conversion System With the GdBCO Magnet

This paper describes the design and test of a high-Tc Superconducting (HTS) power conversion system with the GdBCO magnet and presents its operational characteristics through tests. The HTS power conversion system can be employed to charge and discharge an Energy Storage Magnet (ESM). The HTS power conversion system consists of two heaters, a transformer, and a GdBCO pancake magnet. The energy stored in the dc magnet is converted to ac power via a transformer consisting of an HTS secondary and a normal copper primary. The timing sequential control and thermal transition of heaters are important factors to generate charging and discharging in ESM. In this paper, we verified the feasibility of the HTS power conversion system and obtained the design and manufacturing techniques for scale-up of the system. Based upon the tests, the operating current of 12 A in the transformer and the heater current was optimally derived. The magnetic energy was stored about 46.7 J. In discharging test, the system was converted from dc to ac power at 0.5 Hz and 1 Hz. The efficiency of the system reached about 96%.

Development of the World's First HTS Power Substation

With the increasing depletion of fossil fuels and growing environmental pressure, the mankind has got known the need to vigorously develop the renewable energy and the energy-saving technology. The high Tc superconducting (HTS) power technology will be very helpful to enhance the stability, reliability, and efficiency and transmission capacity of the power grid which would be dominated by the renewable energy. In this paper, we will report the installation and operation of a 10 kV HTS power substation which includes a 75 m/1.5 kA HTS power cable, a 10 kV/1.5 kA HTS fault current limiter, a 1 MJ/0.5 MVA high Tc SMES and a 630 kVA/10 kV/0.4 kV HTS power transformer.

Stability Analysis of HTS Power Cable With Fault Currents

We numerically calculated the transient temperature distribution of flowing subcooled liquid nitrogen in a high-Tc superconducting (HTS) model cable when faults occur. The coolant and cable core temperatures were calculated by numerically solving the heat equation using the finite difference method. In the calculation, we assume that the heat transfer coefficient between the flowing subcooled liquid nitrogen and the cable core surface is described by the Dittus-Boelter correlation. The calculation results reveal that the coolant temperature increases even after the fault has been removed and that it continues increasing until fresh coolant arrives from the inlet. The calculated temperature profile of the coolant agrees well with measured data obtained by conducting over-current tests on a model HTS cable. Using our computational code, we also evaluated the maximum HTS cable lengths that ensure that the coolant remains in the liquid phase for certain fault currents for an HTS model cable.

Study of Structure of Co-axial Multi-layered HTS Power Cable based on Low AC Loss using Efficient 3-D FEM Analysis

Controlling the current distribution in each layer of a co-axial multi-layered high-T c superconducting (HTS) cable uniformly is important in order to realize a compact and large capacity HTS power cable. The phenomenon of current imbalance should be exactly investigated by the analysis, because the current imbalance causes an increase of AC loss. In this paper, 3-D finite element analysis taking account of the nonlinear E-J characteristic is carried out in order to study the AC loss of a co-axial multi-layered HTS power cable with shield layers. The analysis region is considerably reduced by modeling spirally wound superconducting tapes as conductors having an anisotropic conductivity and using the periodic boundary condition. By using this model, AC transport characteristics of the co-axial three-layers cable (composed of two conductor layers and one shield layer) are studied, and the AC loss is investigated. The structure with low AC loss is also discussed.

Experimental Results of a 500 m HTS Power Cable Field Test

The demonstration and verification tests of a 500 m High-Tc superconducting (HTS) cable were carried out at the CRIEPI laboratory in Yokosuka from March 2004 to March 2005. The HTS cable consisted of a cold dielectric core with nominal capacity of 77 kV and 1 kA that had an HTS shield layer. CRIEPI and Furukawa have conducted tests for investigating the basic properties of the cable and a long-term loading test for confirming 30-year operations. Moreover, we conducted an "over-loading test" and a "cooling system fault test" to investigate the reliability and safety of the cable. After all field tests, the cable was dismantled and taken away from the site to Furukawa's factory for internal inspection. No Ic degradation was found in the HTS conductor, but local degradation was seen in the HTS shield. These degradations might have arisen because protective layer for the shield did not have enough thickness but were within the acceptable range of about 5%.

Numerical analysis of the AC losses of 500-m HTS power cable in Super-ACE project

The alternating current (AC) losses of 500-m high- T C superconducting (HTS) power cable in Super-ACE project are calculated by using an electric-circuit model. The cable core is consisted of a former (copper-stranded wire conductor), HTS conductor (Ag/Bi-2223 tapes, 1 layer), electrical insulation (LN 2-impregnated laminated paper), HTS shield (Ag/Bi-2223 tapes, 1 layer) and protection (copper-braided wire). Numerically calculated AC loss (the total loss) is obtained by a sum of the self-field loss and external-field loss (hysteresis losses) consumed at the HTS conductor and HTS shield, the ohmic loss caused by a resistance of copper of the former and protection, and the eddy-current loss caused by an axial field at the former. The calculations are compared with experimental results measured by a calorimetric method. The calculations are almost equal to the measurements at wide transport-current range. At transporting 1 kA rms to the cable, the calculation indicates that the total loss of 1.29 W m −1 (the measurement is 1.3 W m −1) is obtained by a sum of 0.89 W m −1 as the self-field loss, 0.32 W m −1 as the external-field loss, 0.06 W m −1 as the ohmic loss and 0.02 W m −1 as the eddy-current loss. On the other hand, Central Research Institute of Electric Power Industry (CRIEPI) has estimated that the AC loss is obtained by a sum of 0.5 W m −1 consumed at the HTS conductor and HTS shield as the hysteresis loss, and 0.8 W m −1 consumed at the former as the eddy-current loss. The author’s result contradicts CRIEPI’s estimation. It is considered that the difference is caused by an overestimation of the axial field at the former in CRIEPI’s loss calculation.

Analysis on Current Distribution of Four-Layer HTSC Power Transmission Cable with a Shield Layer

The inductance difference between conducting layers of high-T c superconducting (HTSC) power transmission cable causes the current sharing of each conducting layer to be unequal, which decreases the current transmission capacity of HTSC power cable. Therefore, the design for even current sharing in HTSC power transmission cable is required. In this paper, we investigated the current distribution of HTSC power cable with a shield layer dependent on the pitch length and the winding direction of each layer. To analyze the effect of the shield layer on the current sharing of the conducting layers of HTSC power cable, the current distribution of HTSC power cable without a shield layer was compared with the case of HTSC power cable with a shield layer. It could be found through the analysis from the computer simulations that the shield layer of HTSC power cable could be contributed to the improvement of current distribution of conducting layers at the specific pitch length and the winding direction of conducting layer. The result and discussion for the current distribution calculated for HTSC power transmission cable with a shield layer were presented and compared with the cable without a shield layer.

Characteristics Analysis of a High-Tc Superconducting Power Supply Considering Flux Creep Effect

This paper describes the characteristics analysis of a high-Tc superconducting (HTSC) power supply considering flux creep effect, and also presents its operational characteristics through experiments. The power supply can be employed to charge an HTSC magnet. An HTSC power supply consists of two heaters, an electromagnet, a Bi-2223 solenoid, and a series-connected Bi-2223 pancake load. The pancake load was fabricated by connecting four double pancake coils in series. In the experiments, two cases of the pumping period, which correspond to 8.5 and 17 s, were used with an electromagnet of 331 mH and a dc heater current of 0.8 A. A region of the superconducting tape with a buried heating coil can be switched by means of its temperature change. In order to measure the pumping-current with respect to the magnet flux changes, a hall sensor was installed at the center of the Bi-2223 pancake load. The experimental observations have been compared with the theoretical predictions. In this experiment, the pumping-current has reached about 22.9 A

Transient analysis for alternating over-current characteristics of HTSC power transmission cable

In this paper, the transient analysis for the alternating over-current distribution in case that the over-current was applied for a high-TC superconducting (HTSC) power transmission cable was performed. The transient analysis for the alternating over-current characteristics of HTSC power transmission cable with multi-layer is required to estimate the redistribution of the over-current between its conducting layers and to protect the cable system from the over-current in case that the quench in one or two layers of the HTSC power cable happens. For its transient analysis, the resistance generation of the conducting layers for the alternating over-current was reflected on its equivalent circuit, based on the resistance equation obtained by applying discrete Fourier transform (DFT) for the voltage and the current waveforms of the HTSC tape, which comprises each layer of the HTSC power transmission cable. It was confirmed through the numerical analysis on its equivalent circuit that after the current redistribution from the outermost layer into the inner layers first happened, the fast current redistribution between the inner layers developed as the amplitude of the alternating over-current increased.

Electrical Insulation of 500-m High-Tc Superconducting Power Cable

Electrical insulation is one of the essential technologies for the electric power apparatus. Determination of testing voltages and design method of the electrical insulation layer are inextricably linked each other, and are critical to developing and realizing a cold dielectric (CD) type high-Tc superconducting (HTS) power cable. The authors had proposed the electrical insulation design method with concepts of partial discharge-free designs for ac voltage condition. This paper discusses the testing voltages for a 77 kV 1000 A HTS power cable with a length of 500 m, and describes results of various voltage withstand test. As a result, it is concluded that the proposed electrical insulation design method is appropriate for the HTS power cable.

Demonstration of a 500 m HTS Power Cable in the Super-ACE Project

A demonstration of a 500 m single-core high-Tc superconducting (HTS) cable has been carried out by Furukawa, CRIEPI and Super-GM at the CRIEPI site in Yokosuka, Japan. The cable was a cryogenic dielectric type rated at 77kV/1kA. In the test, critical currents (Ic) of HTS conductor and HTS shield at 73 K were 1910 A and 1620 A respectively, with heat invasion of 1.21 W/m, and a pressure drop of 100 Pa/m at an LN2 flow rate of 50 L/min. Rated loading tests corresponding to degradation of the insulation over 30 years were carried out, and there was no degradation in the cable. Moreover, overload and limiting tests were performed under the adverse conditions of over-voltage, over-current and stopping of refrigerators and pumps. After these events, the cable was removed and studied, revealing almost no damage.

RF Power Dependence of Microstrip Disk Resonators With YBCO Films for 4 GHz Band

High-Tc superconducting (HTS) power filters have an attractive possibility of being applied to the base stations of the- future mobile-communication systems. In the microstrip structure, disk-shape-patterned HTS resonators are considered potential candidates for the HTS power filters. In order to research the application feasibility of disk resonators, the resonator samples were fabricated with different quality YBCO thin-films, and the power handling and third intermodulation-distortion (IMD3) of the samples were then examined for the incident continuous wave power of up to about 10 W around 4 GHz at cryogenic temperatures. We discuss the results on the relationship between the RF power dependence and the YBCO film qualities.

Characteristics of critical current of superconducting solenoid wound with the stacked tape

The high- T c superconducting (HTS) magnet is an important element for developing HTS power equipments such as the dc reactor of the inductive type superconducting fault current limiter (SFCL). In order to use the HTS magnet for the large-scale power system, its critical current needs to be high enough. Generally, the double pancake HTS magnet has the severe decrease in the critical current because of magnetic field perpendicular to the tape surface. To fabricate a high critical current magnet, we wound a solenoid with the stacked tape. In this paper, the characteristics of the critical current of the HTS solenoid wound with the stacked tape were investigated. The results of this research can be used as the background data for the design of the large-scale HTS magnet.

Development of important elementary technologies for a 66 kV-class three-phase HTS power cable

High T c superconducting (HTS) cables are expected to serve as underground power lines supplying electrical power to densely populated cities in the future. TEPCO and Furukawa have developed compact HTS cables that can replace the old cables in their existing ducts under metropolitan Tokyo. To connect HTS cables with actual electrical networks requires confirmation of long-term reliability of the electrical insulation and the ability to withstand accidents caused by short circuit. This report gives the results of our examination of these problems.

Test results of a HTS power transformer connected to a power grid

A 22 kV/6.9 kV–1 MVA high- T c superconducting (HTS) power transformer has been developed as a prototype with single-phase part of a 3 MVA HTS power transformer. The prototype unit is cooled by a continuous subcooled liquid nitrogen (LN 2) supply system with cryocoolers. During the field tests, the HTS transformer was connected to a distribution line at Imajuku substation (Kyushu Electric Power Co., Inc.) in Fukuoka, and inrush-current test and a long-term operation test were implemented. The test results demonstrated the HTS power transformer's applicability to a power grid.

Design, fabrication and testing of a high-Tc superconducting power supply with the Bi-2223 load

This paper presents the design and fabrication of a high-Tc superconducting (HTS) power supply. Its characteristics have been analyzed through experiments. A HTS power supply consists of two heaters, an electromagnet, and a Bi-2223 solenoid and a Bi-2223 pancake load. The timing sequential control of two heaters and an electromagnet is an important factor to generate pumping-current in the Bi-2223 load. The thermal analysis of switching parts of the Bi-2223 solenoid according to the heater input was carried out. Based upon the analysis, the 331 mH electromagnet and the 0.8 A DC heater current were optimally derived, and 8.5 sec and 17 sec for the pumping period were selected in this experiment. In the experiment, the maximum pumping current reached 1.7 A.