High Temperature Superconducting Power Research Articles

Оптимизация ВТСП кабелей постоянного и переменного тока с учетом эффекта продольного магнитного поля

It is known that in magnetic fields parallel to the transport current, an increase of the critical current is observed in most low-temperature and high-temperature superconductors — the effect of a longitudinal magnetic field (LMFE). LMFE has been theoretically predicted and experimentally confirmed in many studies. This article presents various methods for optimizing power coaxial cables based on high-temperature superconductors (HTS), considering LMFE. LMFE provides a higher current-carrying capacity of HTS DC cables and higher stability for HTS power AC cables, including lower AC losses. The results of optimization of HTS cables for both DC and AC applications with consideration of LMFE are presented and discussed. Two methods for calculating the magnetic field in coaxial HTS cables are presented: analytical and using the finite element method. The results of AC loss calculations and measurements for HTS cables are also presented.

Understanding ac losses in CORC cables of YBCO superconducting tapes by numerical simulations

Alternating current (ac) losses in conductor-on-rounded-core (CORC) cables of YBCO high-temperature superconducting (HTS) tapes are a significant challenge in HTS power applications. This study employs two finite element analysis (FEA) models to investigate the contributions from different ac loss components and provide approaches for reducing ac losses in cables. An FEA model based on the T-A formulation treats the cross section of thin superconducting layers as 1D lines and, therefore, only can predict the ac loss generated by the perpendicular magnetic field. In contrast, the model based on H-formulation can be performed on the actual 2D rectangular cross section HTS tapes to provide the total ac losses generated by magnetic fluxes penetrating from both the edges and surfaces of HTS tapes, although this model requires more computing time and memory. The 1D and 2D simulation models were validated by cross comparing the results from both models and by comparing sub-section and full cross section models. Subsequently, two models relate cable design and operational parameters to the surface and edge losses of a two-layer CORC cable by considering the (1) relative contributions of edge and surface losses to the overall ac losses; (2) effect of the current distribution between inner and outer HTS layers on ac losses; (3) impact of the tape alignment on ac losses in each HTS layer; (4) influence of the thickness of HTS layers on ac losses; (5) effect of size and number of inter-tape gaps on ac losses; and (6) contribution frequency on the ac losses. The research results given in this paper are therefore not only valuable to suggest strategies for reducing ac loss in multi-layer cables but also for developing more accurate and effective methods to calculate ac loss in CORC HTS cables.

A Numerical Design of High-Resistance and Energy-Efficient HTS Switch Based on Dynamic Resistance

Dynamic resistance effect introduces dissipative loss to the type-II high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> c superconductors, which is initially considered as a disadvantage for superconductors when it was first discovered. However, in some cases “dynamic resistance”, a unique effect, can be effectively exploited. Based on the dynamic resistance effect, the AC-magnetic-field-actuated high temperature superconducting (HTS) power switch is developed. It is the key component in the HTS transformer-rectifier flux pump (TRFP). The operating characteristics of power switch are vital to the performance and reliability of the transformer rectifier flux pump. In this paper, we compare three designs of HTS power switch with different stabilizer structures: striated stabilizer layers with wide and narrow strips as well as original non-striated stabilizer layers. The performance of HTS power switch is evaluated by several criteria, including off-state voltage and resistance, temperature rise, power loss, and energy conversion efficiency. This study will help design high-performance, low-loss, and energy-efficient HTS power switch based on “dynamic resistance” effect.

Estimation on LN2 Level and Condensation of Insulation Gas in HTS Power Cable Termination

The terminations of high-temperature superconducting (HTS) power cables help supply current between the cryogenic HTS power cable and the room temperature power system while maintaining electrical insulation. This involves a cryogenic section with circulating liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) for cooling the HTS power cable and temperature gradient section with level interface formed by thermal equilibrium and an ambient section with current leads and insulation gases such as nitrogen and sulfur hexafluoride (SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ). The level of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> varies depending on the structure of the termination and the operation conditions, and this may further affect the temperature of the ambient section that is installed at the upper end of the cryogenic section. As the level of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> increases, the temperature of the insulation gas decreases and condenses, resulting in a significant decrease in the dielectric strength. Therefore, it is crucial to estimate the level of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> while designing the termination for HTS power cable. In this study, the LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> level of the termination was estimated according to heat load and the operating conditions to avoid dielectric breakdown of insulation gas are proposed using a commercial thermo-fluid network analysis tool, SINDA/FLUINT.

Failure Mode Effects and Analysis of Superconducting Power Distribution and Related Cryogenic Components for All-Electric Ship

Potential failure modes of high temperature superconducting (HTS) devices and related cryogenic systems in electric ship applications are analyzed to understand and plan for the necessary mitigation systems. Risk-based FMEA methodology was adopted to aid in improving the resiliency of large superconducting power distribution systems. A concurrent FMEA study of cryogenic thermal and electrical systems in an HTS power distribution network is discussed. A one-line architecture for a power distribution system was developed to identify the key parameters needed for performing FMEA for HTS power distribution systems. The failure modes are listed to show the interdependence of the electrical and cryogenic systems. The severity and detectability of various failures were used to formulate critical redundancy and mitigation tools to design resilient power distribution systems for electric ships.

Modelling of a High-Temperature Superconductor HVDC Cable Under Transient Conditions

The carbon neutrality goal of achieving net-zero by 2050 has sparked significant interest in offshore wind farms. With the offshore wind farms installed > 100 km away from the seashore, underground power transmission infrastructure is a necessity. Considering the power cable length and low net effective losses, a high-voltage direct-current (HVDC) system is chosen for this study. Also being lossless in DC operation, the HVDC cables are considered to be made out of high-temperature superconductor (HTS) material. But, unlike copper/aluminium, HTS material has a sharp transient behaviour as a function of the operating current, temperature and field. Thus, under transient conditions, as the fault current ramps up, this can lead to an increase in the HTS operating temperature, causing either degradation or permanent damage to the HVDC cable. In this paper, an HTS HVDC cable model has been developed in MATLAB/Simscape coupling both electrical and thermal models. For this study, a 100 km long coaxial 100 kV/1 GW DC HTS power cable is considered and modelled both as a lumped element and distributed element model with 100 elements to compare and evaluate the cable parameters along the length. The parameters include temperature distribution, resistance, critical current, and losses at different spots throughout the length of the cable. To simulate the transient condition, a line-to-ground (LG) fault is considered and the current distribution between the copper former and HTS tapes is studied. Using this cable model, the maximum temperature of the HTS and coolant both in the superconducting state and transient state are evaluated and presented. In comparison to the distributed model, the lumped model displayed different thermal and electrical values.

Influence of Water Content on the Dielectric Characteristics of LN2-Impregnated PPLP for HTS Power Cables

High-Temperature Superconducting (HTS) power cables operate at low, medium, and high voltage levels for electrical power transmission. Polypropylene Laminated Paper (PPLP) is wrapped helically around the HTS layer and it is impregnated with Liquid Nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) to form a composite dielectric layer. During the installation and maintenance process of HTS cables, any leak of moisture in the cryostat will lead to immediate ice formation. Once the cable warms up, the ice will melt into water, which will be absorbed by the PPLP Kraft paper layer and is similar to the PPLP paper soaked with water. When the moist PPLP is cooled with LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> it will form ice and forms a composite material during operation. The objective of this paper is to investigate the influence of water content on the breakdown strength, relative permittivity (ϵ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) and dielectric losses of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> impregnated PPLP samples for different number of layers. Considering the worst-case scenario of moist samples, wet PPLP samples were tested for breakdown strength and dielectric properties at Room Temperature (RT) and LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> temperature and was compared with dry PPLP samples. Two different experimental setups were developed to measure the breakdown strength and dielectric properties respectively for stacked PPLP layers. The wet and dry samples were tested for the AC V-I characteristics, the effect of PPLP stack thickness on dielectric strength, statistical analysis using two parameter Weibull distribution and computation of relative permittivity and loss factor from capacitance measurement.

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&amp;amp;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.

Effect of Moisture Content on the Performance of PPLP as a Dielectric for HTS Power Cable

For the operation of High Temperature Superconducting (HTS) power cables at high voltage levels, the electric field distribution depends on the relative permittivity of dielectric materials. In HTS cables, PolyPropylene Laminated Paper (PPLP) is used as a cold dielectric material and is wrapped helically along the length of the conductor thereby electrically insulating it. During the installation and maintenance process of HTS cables, termination units and joint boxes, the PPLP is often exposed to moisture. The presence of moisture affects the dielectric breakdown strength and dielectric losses. The effect of moisture content in PPLP at ambient and liquid nitrogen temperature has been studied to determine the breakdown strength, relative permittivity (εr) and dissipation factor (tan δ). Effect of moisture content on the performance of PPLP via the measurement of dielectric breakdown strength and relative permittivity for various temperatures and moisture content are discussed in this paper.

Development of Supervisory Control and Data Acquisition System for India’s First High Temperature Superconducting Cable Testing

High Temperature Superconductor (HTS) based power cable is a technological marvel which can transmit bulk power over large distances without any joule heating as compared to a conventional copper cable, owing to its zero DC resistance in superconducting state. However, to maintain this superconducting state, the cable must be at a temperature below its critical temperature under self-field. Commonly used HTS material includes BSCCO (Tc = 110 K) and YBCO (Tc = 93 K) and thus, requires cryogenic liquid nitrogen (77 K) for attaining superconductivity. Further, the voltage drops across the various joints such as joint box and current leads in the termination unit must be monitored to ensure optimal operation of the cable. This demands for sophisticated instrumentation operating under extreme low cryogenic temperatures for safe operation, performance monitoring, cryogenic measurements, and control of the HTS power cable cryogenic process. This paper presents the instrumentation scheme followed for testing India’s first 6-meter HTS power cable. The instrumentation scheme involves housing of the various temperature sensors and location of voltage tapping, current measurement, cryogen flow measurements, operation of control valves, operation and measurement of high vacuum system, stray field measurement, insulation resistance measurement and dielectric measurements for cable are the important parameters for the successful operation of HTS power cable. To perform data logging NI-DAQ and LabVIEW software was used to develop in-house Supervisory Control and Data Acquisition (SCADA) system. This paper discusses intrinsic aspects of complete instrumentation and developed SCADA system for HTS power cable.

Mechanics of dielectric polyamide/ SiO 2 nanocomposite coatings for cryogenic service in superconductor systems

Mechanics of dielectric polyamide/ <scp> SiO ₂ </scp> nanocomposite coatings for cryogenic service in superconductor systems

Comparative Life Cycle Assessment of Different Cooling Systems for High-Temperature Superconducting Power Cables

This study conducts a comparative life cycle assessment of two different types of cooling systems for a 1 km long, 10 kV concentric three-phase high-temperature superconducting cable. In an open cooling system, the required cooling energy is provided by evaporating liquid nitrogen in a subcooler resulting in a constant loss of liquid nitrogen. As a consequence, liquid nitrogen must constantly be reproduced and transported to the cooling unit. Alternatively, a closed cooling system can be used in which liquid nitrogen is electrically re-cooled using a cryocooler. This results in a higher on-site electricity consumption but simultaneously removes any liquid nitrogen losses. It is shown that the use of a closed cooling system does not only reduce the total system losses but also improves the environmental performance by 4–24% depending on the examined environmental impact category. If the cryocooler is powered by renewable energies only, the environmental savings can be increased even further.

Optimized BaZrO3 nanorod density in YBa2Cu3O matrix for high field applications

To maximize the flux pinning in high-temperature superconductor (HTS) thin film applications, we have experimentally studied the effect of BaZrO3 (BZO) nanorod density within the YBa2Cu3O (YBCO) lattice. Even though the BZO decreases the self-field critical current density and the absolute at high fields is observed being the highest for 4% BZO doped YBCO, the maximized pinning property is observed at the level of 10% of BZO, when the distance between the outer edge of the nanorods is in the order of the diameter of the nanorod. In general, as also theoretically calculated, the flux pinning is increased even above 10% of BZO, but the improvement is limited by disturbance of the nanorod growth, weakening the flux pinning and decreasing the absolute drastically. The results evidently show that by maximizing the flux pinning using higher BZO doping concentration than earlier expected and taking care of the maximum self-field , which is strongly dependent on the electron mean free path, would offer the keys to resolve the challenges in the future HTS power applications.

Design of warm dielectric terminations and electrical breaks for high-temperature superconducting power cables

Large electric transportation systems such as electric aircraft and electric ships have been designed with multiple high temperature superconducting (HTS) power cables as part of superconducting power distribution network, and a good electric insulation for the power cables is a critical design requirement needed to be considered. This is because terminations in HTS cable represent a location of significant electrical and thermal stresses and needs to be addressed to reduce the substantial heat load that might be introduced into the cryogenic system. The use of a warm dielectric termination is seen as a potential solution to reduce the electrical standoffs required as part of the design and allow for a high-power dense termination design. A warm dielectric termination design using commercially off-the-shelf ceramic breaks as electrical breaks is explored and withstand and partial discharge measurements are performed to determine the viability of the design concept.

Temperature distribution of long-length high temperature superconducting cable cooled by slush-nitrogen

A numerical model is established to calculate the temperature and pressure distributions of the 3 km long high temperature superconducting (HTS) power cable. The model assumes that the configuration of HTS power cable is three phase co-axial shape with counter-flow cooling method. In the numerical model, the circulating nitrogen enters the inner channel of the HTS power cable for cooling at the one end, flows to the other terminal, returns through the outer channel, and exits from the HTS power cable. The numerical model considers the mass, the momentum, and the energy balances of nitrogen, and the heat diffusion inside the HTS layer to obtain the realistic temperature and pressure distributions of the cable. When the long HTS cable is cooled by subcooled liquid nitrogen, the result shows that the maximum temperature of the compact HTS layer cannot be kept under 80 K even though the subcooled liquid nitrogen is supplied at the melting temperature. In order to supply nitrogen with lower enthalpy for ensuring sufficient cooling through the whole cable region, we suggest using slush nitrogen, and analyze it in the detailed numerical model. Thermo-hydraulic equations for slush nitrogen are incorporated in the numerical model. The results show that the maximum temperature of the HTS layer decreases by 6.4 K when slush nitrogen with solid volume fraction of 30% is supplied to the HTS cable. The effect of the inlet enthalpy of nitrogen and the heat transfer characteristics to the temperature distribution is discussed and further elucidated in this paper.

Design of temperature monitoring system of 35 kV km-Level Domestic Second Generation High Temperature Superconducting Power Cable in Shanghai, China

The city of Shanghai, China plans to deploy the first domestic 35 kV km-level High-Temperature Superconducting Power Cable (HTS-PC) project for connecting two substations in the downtown region in 2021, of which the HTS-PC can transport the current with a maximum value of 2200 A. The HTS-PC needs to operate at a temperature level of the liquid nitrogen temperature zone to maintain the electrically superconducting state. The real-time temperature information of the HTS-PC is crucial for its safe operation. Therefore, this paper proposes a temperature monitoring system suitable for the 35 kV km-level domestic HTS-PC. The system is based on the optical fiber temperature measurement technology and mainly consists of the optical generation, photoelectric detection, fiber sensor, signal acquisition, signal processing, and other components. The conclusion of this paper can be consulted in the operation of the high-temperature superconducting power cable project in the future.

Correction to: Introduction of 35 kV km Level Domestic Second Generation High Temperature Superconducting Power Cable Project in Shanghai, China

A correction to this paper has been published: https://doi.org/10.1007/s10948-021-05931-w

Investigation of Asymmetrical Three Phase Current and Impedance Variation in the Grid Connection of a HTS Power Cable

When a 22.9 kV, 50 MVA HTS (high temperature superconducting) power cable was applied to a real power system and the system was being operated as part of the Icheon project, a current redistribution problem occurred in the shield layer. To clarify the reasons for this, the authors analyzed the characteristics of the current distribution and induced current ratio with a phase angle in the HTS power cable considering an asymmetrical three-phase current that flowed into the conducting layer and the impedance variation of the shield layer according to a grounding method using the PSCAD/EMTDC (power system computer aided design/elector magnetic transients DC) analysis program and vector calculation. It was found that the increases in the asymmetrical current flowing through the conducting layer of the HTS power cable and in the impedance of the shield layer affected the magnitude and phase of the induced current. In addition, depending on the grounding method used, a problem in which the zero current generated by the asymmetry affects the induced current and flows through the cryostat was found. The results obtained through the simulation analysis will provide valuable information for the installation and operation of HTS power cable systems in actual utilities.

Increased Impedance of Wound HTS Power Cables by Quenching at a Shielding Layer for Fault Current Limiting Function

The use of high temperature superconducting (HTS) power cables is viable solution to address the growing demand for electric power, while ensuring low loss and high electric power transmission. Usually, HTS power cables and circular connection of substations reduce grid impedance, and the fault current is increased over the capacity of the circuit breaker. To protect the electric power grid, the fault current should be reduced below the allowable level. Of late, research on HTS power cables having fault current limiting (FCL) functions has increased. An inductive FCL HTS power cable uses the increased inductive impedance caused by magnetic flux leakage to a neighboring iron yoke when a quench occurs at the shielding layer of the cable core due to electromagnetic coupling with the conducting layer. Therefore, there is less heat generation, and the temperature rise is suppressed. In this study, we describe the increased inductive impedance and reduced fault current using a FCL model coil. To demonstrate the electromagnetic coupling between the conducting and shielding layers of the cable core, two concentrically wound REBCO coils were fabricated. The iron yoke inside the coil increases the inductive impedance when a fault current flows through the conducting layer, and quench occurs at the shielding layer. The results are used to develop an FCL HTS power cable with 154 kV, 600 MVA class.

Vibration Testing and Evaluation of 35-kV km-Level Domestic Second-Generation High-Temperature Superconducting Power Cable in Shanghai, China

The 35-kV km-level domestic high-temperature superconducting (HTS) power cable project in Shanghai, China, is expected to be deployed in 2021. Facing the complex operating environment in the metropolitan area, such as the vibration excitation from the subway, pile driving, and seismic activities, the vacuum degree, sealability, and insulation performance of the HTS cables may be affected by the unavoidable mechanical perturbations. The response to the potential vibration excitation is a key factor for the safety and stability of the HTS cables in operation. Therefore, this paper conducts a set of vibration testings for the HTS cable under four kinds of vibration conditions, which include the subway vibration, pile-driving vibration, typical earthquake vibration, and Shanghai artificial wave vibration. Results show that the leakage and outgassing rate of the HTS cable is 1.3×10−6 Pa m3/s at a static state, and increases to 1.4×10−6 Pa m3/s after the vibration testing. The HTS cable exhibits insignificant changes after the vibration testings in the dielectric spectrum examination. The HTS cable can keep its function after the vibration testing that possibly occurred in the metropolitan area.