High Temperature Superconducting Cable System Research Articles

OSCaR: A Cost Analysis of HTS Coaxial Cables With a Novel Optimization Method

The techno-economic convenience of installing a High Temperature Superconducting (HTS) cable rather than a conventional one depends on the type of line and the operating conditions selected. However, the comparisons available in the literature refer to specific case studies and the few cost analyses performed account for a limited number of cable and line parameters. This work presents the costs of a HTS cable system, obtained through a model called OSCaR (Optimization tool for Superconducting Cable Research). The study is focused on the so-called coaxial configuration of AC cables. The optimization tool determines the design of a superconducting cable which minimizes the total cost of the system by varying the voltage, the power and the length of the line. Several geometrical, electrical and fluid-dynamic constraints are imposed. OSCaR allows distinguishing between the different cost indexes and relating them to the individual cable parameters, thus providing useful information on the application limits of the superconducting technology and to guide a cost-effective design. This paper investigates the novel results of parametric analyses obtained with OSCaR, by varying the cable length, the line voltage, the load factor and the cost per unit of length of the superconducting tape. Furthermore, relevant conclusions are reported regarding the minimum distance between adjacent cooling stations to comply with the fluid-dynamic constraints.

Development and demonstration of concentric-type HTS power cable for distribution grid in Shenzhen urban

High-temperature superconducting (HTS) cable can transmit massive power with little dissipation in a limited corridor, which is an attractive solution for future power transmission. Shenzhen Power Supply energized a 400 m/10 kV/2.5 kA concentric HTS cable system on 28 September 2021 to power Ping’an Financial Centre, a Shenzhen’s landmark building, which was the debut of concentric HTS cable made of YBCO in the urban area of a megacity. For more than 1 year, the HTS cable system has been operating well and will continue to operate for a long time. This paper systematically reviews the system specification, cable and its accessories design, cryogenic cooling system design, type and exploratory test, project construction, pre-commissioning test, and operation of the demonstration cable system. Based on our R&D practice, we identify that cost, long-term reliability, and operational simplicity are the main hinders factors that need to be addressed to advance the large-scale application and we propose a set of solution ideas meanwhile.

Time-Frequency Domain Reflectometry for Live HTS Cable System via Inductive Couplers and Neural Network

High-temperature superconducting (HTS) cable has become one of the most promising technology along with an adaptation of a unique superconducting conductor that allows long-distance transmission of the large volume of electronic power with less power loss. Diagnostic and monitoring technique for the reliable and safe operation of HTS cable system has also become a crucial factor to commercialize the HTS cable system in the regarding field. HTS cable system which needs a cooling process for re-activating superconductors is more affected by the loss of cost and time. This paper is proposing the time-frequency domain reflectometry (TFDR) based diagnostic technique for a live HTS cable system. By adapting inductive couplers, the live HTS cable system and the diagnostic signal would communicate without direct contact. Signal attenuation and distortion during the signal induction are compensated by LSTM-based neural network. The proposed method is applied to an AC 154 kV 600 MVA HTS cable system in and is further verified through Advanced Design System (ADS) software.

Dielectric Characteristics of Liquid Nitrogen/Synthetic Paper Composite Insulation System for Extra High Voltage HTS Cable

For extra-high-voltage high-temperature superconducting (HTS) cables, not only high electrical insulation performance but also low dielectric loss is required. Therefore, we focus on a porous synthetic paper with lower dielectric loss, e.g., Tyvek polyethylene nonwoven fabric, than that of polypropylene laminated paper (PPLP), which has been used for a conventional HTS cable insulation system. In this paper, we compare partial discharge inception characteristics for different liquid nitrogen/synthetic paper composite insulation systems. The partial discharge inception electric field strength in the composite insulation system depends on the electric field strength in the porous area of synthetic paper.

Design, Manufacture, and Test of a 30 m 10 kV/2.5 kA Concentric HTS Cable Prototype for Urban Grid

High temperature superconducting (HTS) cable, with significant low dissipation and massive current carrying capability, is a promising solution for the shortage of transmission capacity in mega-cities. China Southern Grid launched a HTS cable project in 2017 to develop a medium voltage concentric HTS cable system for installation in the distribution grid at urban area in Shenzhen City. It is the first time that concentric HTS cable system is developed and will be the first HTS cable installed in urban grid in China. The cable core mainly consists of three concentric phases winded by YBCO tapes and cold dielectric insulations in between phase-to-phase, phase-to-former, and phase-to-screen. The cable has a rated voltage of 10 kV and a rated current of 2.5 kArms. The critical current (Ic) is at least 6 kA per phase. The outline diameter of the cable core is 76 mm and the cryogenic pipe is 175 mm. As a middle step, we designed and manufactured a 30 m long prototype cable system and it was tested generally according to IEC 63075. For improvement of the manufacture processes, several short cable core samples were made, tested, and dismantled. The ultimate goal of the 30 m prototype is to verify the design and accumulate experience for the installation of the 400 m fully functional cable system in the grid. The test results of the 30 m cable prototype are presented and discussed. The 400 m class HTS concentric cable demonstration project has already started and it is expected to energize in grid in late September, 2021.

Demonstration Project of 35 kV/1 kA Cold Dielectric High Temperature Superconducting Cable System in Tianjin

A cold dielectric high temperature superconducting (HTS) cable system, which consists of 100 m three-phase cables, terminals, cryogenic system, and monitoring system, was developed by Futong Group in Tianjin. The rated voltage and rated current of the HTS cable system was designed to be 35 kV and 1 kA, respectively, and the YBCO tapes provided by SWCC were used as the conductors and shielding layers. The HTS cable system was installed at Futong Science Park and put into operation on February 15, 2017. Since then, the HTS cable system has been running stably for more than 20 months with an operating current of ~200 A at a coolant temperature from 72 to 77 K.

Analysis of the thermal recovery of HTS cables after an overcurrent fault

High temperature superconducting (HTS) power transmission cables are cooled to operating temperatures typically below 80 K. A valuable feature of some HTS cables is that they can limit short-circuit fault currents, which can be more than ten times the maximum operating current of a cable. When a fault occurs the HTS wire is no longer superconducting and the heating which occurs will raise the temperature above the allowable operating point. To recover from the fault, the conductor must be cooled down before returning to service. The recovery is affected by the refrigeration system’s performance which varies with load and temperature. A transient numerical model of an HTS cable is applied to investigate the thermal recovery after a fault for some HTS cable system configurations and operating conditions.

Condition Monitoring of 154 kV HTS Cable Systems via Temporal Sliding LSTM Networks

High-temperature superconducting (HTS) cables are expected to be installed in cable tunnels that are already constructed in urban districts. Therefore, the installation of normal joint boxes is inevitable, and it is necessary to develop a diagnostic methodology that considers both the existence of the joints and the electrical characteristics of HTS cables. In this work, temporal sliding long short-term memory (TS-LSTM) is proposed to estimate the locations of the joints that can be hidden by multiple reflections. TS-LSTM includes short-term TS-LSTM and long-term TS-LSTM for analyzing various time dependencies. The reflected signals of the actual joints, which are distinguished from multiple reflections, are analyzed via the chirplet transform (CT) which is one of the time-frequency (TF) analysis methods. The proposed condition monitoring method is applied to an AC 154 kV 600 MVA HTS cable system (1 km) connected to a real power grid network in Jeju, South Korea. For the validation of the proposed methodology, the dielectric and electrical characteristics of the 154 kV HTS cable system are monitored during the cooling process.

Time–Frequency-Based Condition Monitoring of 22.9-kV HTS Cable Systems: Cooling Process and Current Imbalance

In this paper, new time–frequency-based anomaly detection methodology is proposed for the condition monitoring of high-temperature superconducting (HTS) cable systems. The time–frequency-based anomaly detection methodology includes two indices, which are obtained via cross Wigner–Ville distribution and scattering parameter. For the validation of the proposed methodology, the methodology is applied to an ac 22.9-kV/50-MVA HTS cable system connected to the real power grid network. Furthermore, the changes in dielectric properties of the HTS cable system during the cooling process and the current imbalance failure are monitored. The proposed anomaly detection indices are shown to be able to detect the heat and the current imbalance caused by the malfunction of the joint box. For the application of the two validated indices, new anomaly detection procedure for HTS cable systems is also presented.

Recent Progress of the High-Temperature Superconducting Cable Project in Japan

We have spent considerable time studying high-temperature superconducting (HTS) cable for a long time. In Japan, a national project of the HTS cable system in a real grid operation, funded by the New Energy and Industrial Technology Development Organization (NEDO), started a decade earlier, which meant we could carry out real system operation for a year several years ago. We subsequently studied two issues on a new national project. One involved improving the performance of the cooling system, while the other involved safety verification against events possibly occurring in a system such as a ground fault or a short circuit. I will report on the outline.

Impact of Smart HTS Transmission Cable to Protection Systems of the Power Grid in South Korea

In South Korea, Korea Electrotechnology Research Institute (KERI) has developed a 154 kV smart High Temperature Superconducting (HTS) cable system with fault current limiting function since May 2017. This project is funded by the Ministry of Trade, Industry, and Energy of Republic of Korea. It is very important to design the protective relay system for a successful application of the smart HTS cable system to a practical power grid. In general, the smart HTS cable can have a negative impact on the protective coordination in power transmission system because of the variable impedance of the cable. This paper reviews some protection problems which can be caused by the application of the 154 kV smart HTS cable to power transmission systems in Korea and proposes a protection scheme for a test power system. And then we conduct a basic study to find solutions for the problems using an electromagnetic transient program, PSCAD/EMTDC.

Fluid characteristic of liquid nitrogen flowing in HTS cable

For long distance operation of High-temperature superconducting (HTS) cables, evaluations of heat transfer and fluid flow dynamics of liquid nitrogen (LN2) flowing in the HTS cable is important. However, the LN2 flow is complicated when the cable core is housed in a spiral corrugate cryostat-pipe and positioned at an eccentric position to the center of the cryostat-pipe. In this study, the effect of a configuration of a spiral corrugate cryostat-pipe on the pressure drop was evaluated using computer simulation. As a result, it was confirmed that the calculated pressure drop in the spiral corrugate pipe is 17 times larger than that in the straight pipe due to the shrinking and expanding of the LN2 flow at the concave domain. This shrinking and expanding of LN2 flow was assumed to be the flow in a gradual contraction pipe and a gradual expansion pipe respectively, so that the pressure drop was calculated by a theoretical arithmetic analysis. For verification of this calculation, the calculated value was compared with the measured value of a HTS cable system, which was constructed in NEDO project. As a result, these values were agreed well each other and it indicated that the pressure drop in the spiral corrugate pipe could be evaluated by this calculation.

Monitoring Method for an Unbalanced Three-Phase HTS Cable System via Time-Frequency Domain Reflectometry

In this paper, we propose a new time-frequency based analysis method that monitors the state of the high temperature superconducting (HTS) cable system in a real-time manner and detects the current imbalance of HTS cable system. The new time-frequency-based method utilizes the cross Wigner-Ville distribution to analyze the time-frequency localized phase difference of the reflected signal, which varies depending on the insulation characteristics of the HTS cable system. Also, a real-world AC 22.9 kV 50 MVA HTS cable system and a current source are used to validate the performance of the new monitoring method in order to detect current imbalance phenomenon.

Safety Verification of a 275-kV HTS Cable System Under Short-Circuit Current Accidents

A simulation code that analyzes the temperature and pressure in a high-temperature superconducting (HTS) power cable cooled by a forced flow of subcooled liquid nitrogen (LN) has been developed. Analysis of the HTS cable is useful for comprehending the normal operating condition and the generation of heat during the transient state. In Japan, an excessive current of 63 kA may flow in an HTS cable for 0.6 s in the worst case when a short-circuit current accident occurs in a 275-kV class cable. To assess the safety under this condition, a simulation of a 275-kV class 20-m model cable was performed, and the simulation results of the temperature profiles qualitatively agreed with the experimental results. In this study, a finite-difference method was used to solve the nonlinear partial differential equations of the heat-transfer phenomenon through heat conduction. By solving these equations, the temperature profiles of the LN coolant and the cable cores were analyzed. The GASPAK software package (Cryodata) was used to evaluate the fluid properties when the LN temperature in the cable was calculated. According to this result, the simulations focused on the analysis of a real-scale HTS cable in this work.

Monitoring Electrical and Thermal Characteristics of HTS Cable Systems via Time–Frequency Domain Reflectometry

A high-temperature superconducting (HTS) cable system with the 22.9 kV, 50 MVA, and 410 m length is installed and operated at 154 kV Icheon substation of Korea Electric Power Corporation (KEPCO). Unfortunately, it is a difficult task to diagnose and monitor electrical and thermal characteristics of the HTS cable system in a real-time manner. In order to protect operational failures of grid-connected HTS cable systems, this paper proposes time-frequency domain reflectometry (TFDR) and analysis techniques, i.e., time-frequency cross correlation and instantaneous frequency estimation. To verify the performance of the proposed method, the temperature is changed via the cryogenic refrigeration system and the status of the grid-connected HTS cable is monitored via TFDR in a real-time manner.

Temperature and Pressure Simulations of 66 kV 40 m HTS Cable System in Short-Circuit Current Accidents Compared With Experimental Results

A numerical analysis program has been developed to simulate the transient temperature and pressure distribution in an high-temperature superconducting (HTS) power cable cooled by a forced flow of subcooled LN2 during a short-circuit current accident. This computer simulation program includes computations of temperature and pressure profiles not only in the HTS power cable itself, but also in the cooling system, including the circulation pump. In 2015, Sumitomo Electric Industries demonstrated a 66 kV 40 m model cable with a fault current test, during which the void between the copper conductors of the copper former was filled by insulation material. In this study, simulations of the model cable were performed by considering that LN2 is not absorbed in the copper former. This simulation was found to more precisely match experimental data by considering the rise in LN2 temperature at the inlet and transient value of the thermal conductivity of the dielectric layer.

Transient Thermal Finite Element Modeling of HTS Cable Systems Cooled With Gaseous Helium

Intensive thermal modeling for gaseous helium cooled high -temperature superconducting (HTS) power devices is necessary for understanding the dynamic thermal behavior during potential system contingencies. This paper presents a transient analysis of an HTS cable system that uses helium gas as a cryogen in a closed loop. Several system contingencies in which the system undergoes a transition that may lead to quenching are simulated. These contingencies include: a vacuum breach, cryocooler failure, and a combination of cryocooler and gas circulation impeller failure. Additionally, the thermal mass of the cable termination is varied to analyze its importance and effect on the timescale for the system to reach a critical temperature of 80 K.

Fundamental Study of Ground Fault Accident in HTS Cable

High-temperature superconducting (HTS) power cable has significant merits of compactness and large power transmission capacity. Although the stability of the HTS cable system was verified by in-grid operation, the verification of its safety and reliability against various accidents is required for practical use of this system. A ground fault accident is one of the typical accidents of a conventional cable. If this fault occurs by breakdown of the dielectric layer, the generated arc energy is dissipated into the environment in various forms. As a result, the safety of the public may be jeopardized. Arc energy relates to arc voltage, which is dependent on the inherent physical properties of the faulted equipment. The use of coolant and the structure of the HTS cable differentiate it from a conventional cable, so it should be verified how these differences influence the arc voltage. Accordingly, ground fault tests using the HTS cable were conducted and the arc voltages were compared to that of a conventional cable. The results obtained proved that the arc voltage on the HTS cable is similar to that of a conventional cable, in spite of the differences concerning the use of coolant and the cable structure.

Development of 35 kV 2000 A CD HTS Cable Demonstration Project

With funding support from Science and Technology Commission of Shanghai Municipality (STCSM), China's first cold dielectric insulation (CD) high-temperature superconducting (HTS) cable system has been developed. The HTS cable system consists of 50-m three-phase cables, six terminations, one refrigeration system, and one remote monitor control system. And it was designed to have transmission capacity of 120 MVA (rated voltage 35 kV, rated current 2000 A). In its conductors, 2G HTS tape that was provided by American Superconductor was selected. The HTS cable was installed in Baosteel Company Ltd., and was successfully put into operation on December 9, 2013. An unmanned remote monitor control power station has been built by highly intelligent control and communication technology. The project is led by the Shanghai Electric Cable Research Institute with a team of Shanghai Sanyuan Cable Accessories Company Ltd., BaoSteel Company Ltd., and Shanghai Electric Power Design Institute Company Ltd. Shanghai University, Shanghai Jiaotong University, and Shanghai Cable Company Ltd. are also involved in the projects.

Investigation on Effective Operational Temperature of HTS Cable System considering Critical Current and AC loss

The operational cost for maintaining the superconductivity of high-temperature superconducting (HTS) cables needs to be reduced for feasible operation. It depends on factors such as AC loss and heat transfer from the outside. Effective operation requires design optimization and suitable operational conditions. Generally, it is known that critical currents increase and AC losses decrease as the operational temperature of liquid nitrogen (<TEX>$LN_2$</TEX>) is lowered. However, the cryo-cooler consumes more power to lower the temperature. To determine the effective operational temperature of the HTS cable while considering the critical current and AC loss, critical currents of the HTS cable conductor were measured under various temperature conditions using sub-cooled <TEX>$LN_2$</TEX> by Stirling cryo-cooler. Next, AC losses were measured under the same conditions and their variations were analyzed. We used the results to select suitable operating conditions while considering the cryo-cooler's power consumption. We then recommended the effective operating temperature for the HTS cable system installed in an actual power grid in KEPCO's 154/22.9 kV transformer substation.