HTS Cable System Research Articles

HTS Cable and Protection System Study for U.K.’s 275 kV Transmission Network

HTS Cable and Protection System Study for U.K.’s 275 kV Transmission Network

Environmental Life-Cycle Assessment of a 10 Kv High-Temperature Superconducting Cable System for Energy Distribution

This study conducts a life-cycle assessment for the use of superconducting medium voltage cables based on the AmpaCity cable in Germany. The results are compared with the use of a conventional high voltage cable. For the conventional cable, additional transformer losses are included, while for the superconducting cable the operation of the necessary cooling system is considered. The annual transmitted energy represents the functional unit. The annual loss energy of the HTS cable system is lower than that of conventional cable from a load factor of m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> = 0.43. This load factor also represents the ecological break-even point. For a load factor of m <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> ≥ 0.43, the greenhouse gas emissions and cumulative energy demand of the superconducting cable system are lower than those of the conventional cable system. Thus, if the load is sufficiently high, a superconducting cable can thus be a more environmentally friendly alternative for a future energy system.

Condition Monitoring Technique of HTS Cable via Tangent Distance-Based Template Matching Coefficient

To obtain reliable operating of HTS cable system, temperature and pressure are commonly used as condition monitoring parameters. However, the sensors for the parameters are attached only at the terminals or joints of the HTS cable; therefore, the conventional parameters are not suitable to detect the inward change of the HTS cable. In this paper, tangent distance-based template matching (TDTM) coefficient is proposed to monitor the condition of the HTS cable. TDTM technique is applied to time-frequency domain reflectometry (TFDR) which is an advanced fault localization technique, and the TDTM coefficient is calculated during the template matching. A single phase HTS cable is utilized to verify the performance of the TDTM coefficient, and baseline results are measured at 300 K and 77 K in the test bed. It is expected that the proposed TDTM coefficient can be used for stable operation and monitoring of the HTS cable system.

Insulation Characteristics and Fault Analysis of HTS Cable via Stepped Frequency Waveform Reflectometry

The characteristics of the HTS cable including conductivity, permittivity, and insulation characteristics vary depending on the conditions of temperature and pressure during operations. We propose a diagnostic method that estimates the propagation constant of the HTS cable and detect the location and the degree of the fault using stepped frequency waveform reflectometry. The performance of proposed method is verified by the HTS cable experiment regarding the propagation constant estimation and the fault detection. The results of HTS cable cooled by the liquid nitrogen are also compared with the results at the room temperature to analyze the insulation characteristics change according to the state. The proposed method is expected to be further applied to monitor the condition of HTS cable system regarding temperature and pressure.

Overcurrent Characteristics on a 22 kV/12 kA HTS Model Cable

Generally, electric power is transmitted from a generator through a step-up transformer to high-voltage transmission lines. The feeder from the generator to the step-up transformer is often installed with an aluminum bus line and so on because the current through the feeder is quite large; likely more than 10 kA. Even a superconducting cable can transmit a large current in compact size, so this type of feeder from a generator is expected to be one of the applications of superconducting cables. Therefore, together with Tokyo Electric Power Company, we have been developing HTS cables for feeder lines and constructed a 10-m model cable with 22-kV/12 kA capacity. Several performance tests were conducted on the model cable, including critical current measurement, nominal current application, ac loss measurements, and ac voltage withstanding tests. Overcurrent tests were also conducted. In the TEPCO grid of 22 kV, a fault current is estimated to be 63 kA for 0.6 s. Because the fault current is about five times larger than the nominal current of 12 kA, when such a large fault current goes through an HTS cable, the superconductor is expected to return to the normal state to make a large amount of heat generation. These phenomena may cause a variety of problems. Due to the limitations of the current supply apparatus, the overcurrent tests were conducted with dc current instead of ac current at an LN2 temperature of 77 K and pressure of 0.2 MPaG. The critical current of HTS cable was 19 kA, and the dc overcurrent was 38 kA for 5 s, with the generated energy estimated to be greater than that from 63 kA for 0.6 s. Test results showed the maximum pressure increase to be approximately 20 kPa, which is not so large as to cause problems. The critical current tests of the HTS cable found no degradation between before and after condition. However, it is not certain whether significant pressure increases might happen in a longer HTS cable system, such as an actual case 100 m long. Therefore, we have also been developing a simulation code and will compare the experimental result with the analytical one.

Analysis of terminal heat loss of 10kV/6000A high temperature superconducting cable

HTS power cable terminal is an afflux unit of transition from superconducting cable operating at low temperature to high voltage bus and outlet of refrigerant in normal temperature. In order to obtain the low-temperature environment for the stable operation of 10kV/6000A superconducting cables, we designed a terminal system. The terminal is refrigerated by circulating liquid nitrogen, and the heat loss of the terminal is calculated to obtain. The current leads in the terminal are optimized and the optimal structure lead dimensions are obtained and finally it is verified by experiments. The results show that the leakage heat value of the terminal is about 590W, and the current lead is the most important leakage heat source. The calculation results provide a basis for the design and further optimization of the HTS cable terminal cryogenic system.

Design of 23kV 50MVA class HTS Cable in South Korea

The world first commercial project for the superconducting applications is already starting in South Korea. The first step of the project named SSS (Superconducting Smart platform Station in South Korea) is to operate AC 23kV 50MVA class HTS cable system in the power grid of Korea Electric Power Corporation (KEPCO) in order to increase the power capacity and realize the stable operation. The above HTS cable system will connect two substations between ShinGal and HeungDuk. Total length of the HTS cable is approximately over 1km including 2 sets of the normal joint box and 2 sets of the termination which are the out-door type accessories. Before performing the type test, various preliminary tests with the short cores were performed to confirm design of the HTS cable. To meet the design goals, the HTS layers of the core consist of the two conducting and one shield layer. The characteristics of the HTS wire is the non-magnetic 2nd generation wire. It can reduce the magnetization loss caused by itself and adjacent the HTS wires. The measured AC loss is around 0.3 W/m at 1,260 Arms and increasing trend of AC loss by operating current is the well fitted of simulation results. In case of short-circuit test, experimental temperature is approximately 77K and increased maximum temperature is under 92.8 K which is enough below the boiling temperature of LN2 at gage pressure 6.7bar.(g). A 70-meter-long the HTS cable including unit the test samples and an 85-meter-long LN2 return pipe will manufacture and installed for the type test at KEPCO Power Training Center in Gochang, South Korea. The type test procedure is following the Cigre TB538 and KEPCO standard those are including the 20 cycles load test, voltage tests such as AC withstand and impulse, repeated cooling process three times as prequalification quality test and visual inspection after disassembling. In the third quarter of 2018, LS Cable&System will supply and install AC 23kV HTS cable system in South Korea.

Installation Design of 23kV 50MVA class HTS Cable in South Korea

As an initial step of this innovation, in September of 2016, KEPCO (Korea Power Electric Corporation) has launched the world first commercial superconducting cable project, named SSS (Superconducting Smart platform Station in South Korea) project, which will be not only the first commercial trial in the grid but also a test bed for Smart Superconducting Platform in South Korea. The main target design of this project is installation of 23kV 50MVA class HTS cable a system in the power grid. Type of this HTS cable is 3 phases in One Cryostat which is a remarkable way to transfer large power with low voltage and no electric magnetic field that means prevention of heating of other cores of phases and two metal sheaths of the cable. Total length of HTS cable between ShinGal and HeungDuk substations is slightly over 1km and it has 2 sets of normal joint box and 2 sets of termination. In this HTS cable system, a mechanical stress during the cool-down and warm-up is a major issue for increasing stability to set-up the HTS cable system and to connect existing power lines. To solve this issue of SSS project, we developed a simulation program which used Equivalent Solving Method for reducing and predicting thermal contraction force of the HTS cable under the mechanical stress. Also, mechanical strengths of metal sheaths, that made of aluminium material and the former that was stranded of copper wires was measured by the tensile tests. Coefficient of elasticity and thermal expansion according to various temperatures was calculated by the experimental data. And then, the analytical method was applied to verify installation method by approximate 40m length HTS cable that has various installation conditions such as vertical shape, often called snake method, at straight route in installation path. From the above procedures, we find that mechanical strength of each component of the HTS cable can calculate according to installation route in the power grid.

Effect of high voltage electrical breakdown on critical current of High Temperature Superconducting tapes

Effects of high voltage electrical impulse events on the critical current of 2G HTS tapes are studied experimentally to develop an understanding on the potential damage that could occur if superconducting cables undergo electrical breakdown. The need for understanding the degradation is discussed in the context of the superconducting gas insulated lines (S-GIL), a novel design concept for superconducting cables. Since the S-GIL uses the gaseous cryogen as the sole insulation system which does not degrade in an electrical breakdown event, it is essential that the superconducting tapes themselves stay undamaged for the HTS cable system as a whole to be operational after electrical breakdown. Critical current of 2G HTS tapes were measured before and after subjecting them to electrical impulses at various voltage levels. It is shown that the extent of degradation depends on the number and voltage level of the impulses. The results of degradation of critical current are discussed in terms of the total energy released in an impulse event.

Cryogenic System for 80-kV DC HTS Cable in the KEPCO Power Grid

DC HTS cable has advantages in the absence of ac loss. Therefore, the Korea Electric Power Corporation (KEPCO) has started a project of operating and manufacturing technology for applying an 80-kV 500-MW 500-m-long dc HTS cable to the commercial power grid since 2011. LS Cable Ltd. has joined this project for designing and manufacturing an HTS power cable, and KEPCO has taken on cryogenic system and real power grid operation. The cryogenic system for an 80-kV dc HTS cable is composed mainly of Stirling-type cryocoolers. The Stirling cryocooler has been examined and verified by real grid operation in Icheon substation, and we therefore became assured of reliability for the cooling HTS cable system. We present the cryogenic system design, installation, and some results of preliminary tests in this paper.

Plate-fin Heat-exchangers for a 10 kW Brayton Cryocooler and a 1 km HTS Cable

Plate-fin heat exchangers (PFHX) are designed and fabricated for a cryogenic cooling system, serving for a 10 kW Brayton cryocooler and a 1 km HTS transmission cable under development in Korea. To achieve compactness and thermal efficiency at the same time, a recuperative HX for Brayton cycle and a sub-cooling HX of liquid nitrogen for HTS cable are designed as integrated parts. A key design feature is focused on the coldest part of sub-cooling HX, where the streams of liquid nitrogen and refrigerant (helium gas) are arranged as two-pass cross-flow so that the risk of freeze-out of liquid nitrogen can be reduced. Details of hardware PFHX design are presented and discussed towards its immediate application to the HTS cable system.

Dynamic Characteristics of Pressure Build Up Tank for HTS Power Cable Refrigeration System

HTS power cables are cooled by the forced circulation of sub-cooled liquid nitrogen to remove heat loss and maintain a cryogenic temperature. The refrigeration systems used consist of cryocoolers, a pressure build-up tank, heat exchangers, and circulation pumps. Liquid nitrogen expands or shrinks according to the temperature variation inside the fixed volume of the refrigeration system and the cable cryostat. The system pressure also changes depending on the volume change of the liquid nitrogen. The pressure of the liquid nitrogen should be kept above a certain level to ensure its dielectric strength. In addition, the pressure should be kept below the allowable pressure level considering the mechanical strength of the refrigeration system.To enhance the pressure controllability, external heating and cooling should be possible in the pressure build-up tank. For the precise modeling of the pressure build-up tank, thermal stratification and axial thermal conduction are considered. An analysis of such a refrigeration system is performed using the commercial code ‘Sinda/fluint’, a comprehensive finite-difference, one-dimensional, lumped parameter tool. This paper presents the transient thermo-hydraulic characteristics and the design directions of an HTS cable refrigeration system according to a variable heat load including pressure build-up tank.

Installation and Power Grid Demonstration of a 22.9 kV, 50 MVA, High Temperature Superconducting Cable for KEPCO

Korea Electric Power Corporation (KEPCO) has a great interest on the application of HTS cable to its network to relieve power congestion and enhance the reliability of the power system. Down through the years from 2005 to 2010, the 22.9 kV, 50 MVA HTS cable has been demonstrated by field test, showing affirmative results. With the financial support of Ministry of Knowledge and Economy (MKE), the new project to install and operate the HTS cable in electrical network of Korea was launched in 2008. An HTS cable with the 22.9 kV, 50 MVA, and 410 m length was installed in the KECPO grid in the end of 2010. After the integration of the HTS cable system, the commissioning items of the DC withstand voltage test, DC critical current test, and heat loss measurements were conducted in accordance with the Korean industrial standard, and self-defined specifications. The HTS cable was energized on the 154 kV Icheon substation of KEPCO on August 19th, 2011. The details of the project description, onsite installation, and commissioning tests are presented in this paper.

Development of 66kV class REBCO superconducting cable

Abstract Sumitomo Electric Industries (SEI) has been involved in the development of 66 kV/5 kA-class HTS cables using REBCO wires. One of the technical targets was to reduce the AC loss to less than 2 W/m/phase at 5 kA. SEI developed a clad-type textured metal substrate with lower magnetization loss than NiW substrates. REBCO wires of 30 mm wide were slit into 4 mm-wide strips, and these strips were wound spirally on a former with small gaps. The measured AC loss of the manufactured cable was 1.8 W/m/phase at 5 kA, achieving the AC loss goal. Another important target was to manage fault current. The copper protection layers were designed based on simulation findings. Fault current tests (max. 31.5 kA, 2 sec) showed that the designed HTS cable has the required withstanding performance. The development of the elemental technologies was finished on schedule, and a 15 m-long HTS cable system will be constructed to demonstrate that it meets all the required specifications.

Recent Progress of Liquid Nitrogen Cooling System (LINCS) for Yokohama HTS Cable Project

Abstract Adopting a high temperature superconducting cable system into the power grid has been studied and demonstrated around the globe because of its inherent high potential for such high transmission capacity, low electrical loss, environment friendly operation and so on. Taking their benefits for the innovative power transmission system into consideration, a new Japanese HTS cable project has begun since 2007, which is supported by Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO) and is verifying practical use of the system in the real grid. For investigating this study, a practical use of the HTS cablesystem composed of cable, joint and termination, operating stability and long term reliability of its liquid nitrogen cooling system is one of the essential engineering to be studied and confirmed for the next real in grid system in this project. In this paper, project outline, fundamental characteristics of the cable system, conceptual design of the cooling system for the demonstration project are introduced. And some test results of them, including a cooling system pre-test in Mayekawa factory prior to final operation in Yokohama test site are presented. This pre-test was conducted with the aim of confirming their required basic performance, liquid nitrogen control characteristics and so on. Finally the current status of Yokohama testing site will be also described in this paper.

Test Results of a 30 m HTS Cable for Yokohama Project

HTS cable demonstration project supported by Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO) has started in Japan. The target of this project is to operate a 66 kV, 200 MVA HTS cable in the live network of Tokyo Electric Power Company in order to demonstrate its reliability and stable operation. The design of the HTS cable with DI-BSCCO has been completed as well as those of a termination and a joint. A 30-meter HTS cable system with terminations, a joint and a cooling system was installed in SEI facility to confirm their design and performance. Various tests as voltage tests, nominal and over current tests, heat cycle tests, heat loss measurements and so on were conducted and it is verified that the cable has good performances as design. This paper describes the design and test results of a 30-meter HTS cable, and discusses required test items of HTS cables.

HTS cable design and evaluation in YOKOHAMA Project

HTS cable demonstration project supported by Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO) has started since FY 2007 in Japan. The target of this project is to operate a 66 kV, 200 MVA HTS cable in the live network of Tokyo Electric Power Company (TEPCO) in order to demonstrate its reliability and stable operation. Various preliminary tests with the short core samples were conducted to confirm the HTS cable design. One of the technical targets in this project is to reduce the AC losses of HTS cable cores. For this purpose, a new type DI-BSCCO wire with twisted superconducting filaments which is named TypeAC is applied in the cable core. A short cable core made with TypeAC wires shows its AC loss is 0.8 W/m/ph at 2 kArms, which is about 1/4 of the one with standard DI-BSCCO wires. Another important target is to manage a fault current. At a preliminary test with the short cable cores, it showed that the cable could manage the through-fault of 10 kA at 2 sec and survived at 31.5 kA at 2 sec. As the electric insulation tests, AC 90 kV for 3 hours and lightning impulse at ±385kV, 3 shots for each were applied to a cable core, successfully. The results of tensile and bending tests showed the cable core has good mechanical properties. The design of the HTS cable for YOKOHAMA project has been completed as well as those of a termination and a joint. A 30-meter HTS cable was manufactured and a 30-meter HTS cable system was installed in SEI facility. The cable system was cooled down and tested to verify its performance before constructing the HTS cable system in YOKOHAMA. This paper describes the design and test results of the 30-meter HTS cable, and also performance test results of the 30-meter cable system.

Test results of a 30-m HTS cable pre-demonstration system in Yokohama project

High temperature superconducting cable demonstration project supported by Ministry of Economy, Trade and Industry and New Energy and Industrial Technology Development Organization has started since FY 2007 in Japan. Target of this project is to operate a 66kV, 200 MVA HTS cable in a live grid in order to demonstrate its reliability and stable operation. A demonstration site has been decided to Asahi substation which is located in Yokohama. The cable length will be decided to between 200 and 300m depending on a site configuration. Various preliminary tests such as critical current, ac losses, fault current loading, mechanical tests, have been conducted by using short core samples in order to confirm a HTS cable design and a cable-to-cable joint structure. From these test results, a HTS cable, a joint and a termination have been designed to meet the required specifications. To verify their performances before the installation of the HTS cable system in Yokohama, a 30-m HTS cable was manufactured and various sample tests were conducted as shipping test. The critical current of the HTS conductor and shield were 6.1kA and 7.1kA, respectively. The AC loss was 0.83W/m/ph at 2kArms, 60Hz. As withstand voltage tests, AC 90kV for 3h and lightning impulse at ±385kV were applied to cable core, successfully. These test results has confirmed that the 30-m cable had good properties as designed and satisfied the required specifications. After the success of the shipping tests, the 30-m HTS cable pre-demonstration system has been installed at SEI factory. The cable system will be operated and checked the various performances in this summer.

단층 초전도케이블 샘플에서 교류손실의 수치해석에 대한 연구

AC loss is one of the important factors for commercialization of a high temperature superconducting (HTS) cable from an economic point of view. But AC loss characteristics of the HTS-cable are not elucidated completely because of its complex structure. As an earlier stage of analyzing the AC loss in the 22.9 kV/50 MVA, 100m HTS-cable system of Korea Electric Power Corporation (KEPCO) which is now in collaboration with us, a two-dimensional (2D) numerical model, which takes into account the nonlinear conductivity properties of a high temperature superconductor, has been developed. In order to examine our 2D model, we have prepared several single-layer cable samples whose AC losses are sufficiently reliable due to their simple structure. The AC losses of the samples were experimentally investigated and then compared with our 2D model. The results show that the numerically calculated AC losses are not in good agreement with the measured ones for the cylindrical cable and deca-cable samples with low critical current density. However, the numerically calculated and measured AC losses are relatively in good agreement for the deca-cable and hex-cable samples with high critical current density, although the difference between these two loss data in the deca-cable sample tends to increase in the low current region.

A New HTS Cable Project in Japan

A new HTS cable project supported by Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO) has just started in Japan. Target of this project is to operate a 66 kV, 200 MVA HTS cable in a real grid in order to demonstrate its reliability and stable operation. Tokyo Electric Power Company (TEPCO) provides the real grid and studies the impact of connecting the HTS cable to the existing conventional facilities in Yokohama. Sumitomo Electric Industries, Ltd. (SEI) designs and manufactures the HTS cable, terminations and joint. Mayekawa Mfg. Co. Ltd. provides a cooling system. Total project period is planned to be 5 years. In 2007, components of HTS cable system were studied and designed. In 2008 and early 2009, the pre-system with a 30-meter cable will be installed in the factory to demonstrate basic performance of the HTS cable and its accessories. Then the 200 MVA HTS cable will be manufactured in 2009 and installed and operated at the site in 2010 and 2011. One of the technical targets in this project is to reduce the AC loss of HTS cable. For this purpose, a new type DI-BSCCO wire with twisted superconducting filaments is planned to be applied in the cable. A 1-meter cable core manufactured with the new wires shows its AC loss as less than 1 W/m/ph at 2 kArms, which is 1/4 of AC loss with normal DI-BSCCO.