Superconducting Power Cables Research Articles

Thermal-electrical analogy for simulations of superconducting power cables

Due the integration of superconducting technologies into electrical networks around the world, its precise simulations in power grids are increasingly becoming a desirable outcome. Over the years, sophisticated methods have been used to model superconducting power cables and, in this way, predict its behavior under different conditions. Most of the available models, however, are not advisable to be used and embedded in power system simulators. In this manuscript, we focus on the development of a method specifically for modeling superconducting cables in traditional power grid simulators. We start developing the model through a case example, within the basic concepts are introduced and later expanded to general cases. The model also incorporates the transient behavior of the cooling media, which is mandatory for such cables. It has been observed that the proposed model requires less computational effort and is able to deliver accurate results when compared to more advanced methods.

Modelling and optimization of cryogenic mixed-refrigerant cycles for the cooling of superconducting power cables

For the green energy transition, the transport of large amounts of electrical energy is needed both in densely populated areas and over long distances. Superconducting power cables represent one possible solution, requiring energy-efficient liquid nitrogen re-cooling stations for an economical operation at cable lengths longer than about 1 km to 2 km.In this contribution, a model for simulating cryogenic mixed-refrigerant cycles (CMRC) based on the Joule-Thomson effect and an associated optimization algorithm are presented. The distinctive feature of CMRC is the combination of good scalability of the cooling capacity, adaptability of the mixture to the specific application and an inexpensive process design. While the process is relatively simple, the identification of ideal operating conditions and mixture compositions requires complex modelling. In order to optimize these characteristics for CMRC processes, the Differential Evolution algorithm is adapted to a model built in Mathematica. Thermodynamic property data is calculated with the Peng-Robinson Equation of State as part of CoolProp, an open-source thermophysical property library. First simulation results are presented and further improvements are being discussed.

Test Station for High Temperature Superconducting Power Cables

Test Station for High Temperature Superconducting Power Cables

MgB2-Based MVDC Superconducting Power Cable in Liquid Hydrogen for Hybrid Energy Distribution

MgB₂-Based MVDC Superconducting Power Cable in Liquid Hydrogen for Hybrid Energy Distribution

Evaluation of Lapped Tape Electrical Insulation for Gaseous Helium Cooled High Temperature Superconducting Power Cables

Evaluation of Lapped Tape Electrical Insulation for Gaseous Helium Cooled High Temperature Superconducting Power Cables

Electrical Tests and Current Distribution of 500-m-Long DC Superconducting Power Cable

The third cooling test of 500m-long superconducting DC power transmission (SCDC) line constructed in Ishikari city, Hokkaido, was carried out in 2021. The system consists of underground superconducting cable with its electric capacities, 5kA and 100MVA. After completing two cooling tests in 2015, the system remained in a shutdown state. Therefore, this test was the first operation test in six years. The targets of the 3rd cooling test were to confirm the presence/absence of the damage due the Hokkaido Eastern Iburi Earthquake (Mj.6.7) that occurred in and acquire basic data for improving the efficiency of SCDC. Regarding electrical tests, the various tests, such as the capacitance/dielectric loss tangent temperature characteristic measurement, the insulation resistance measurement, the DC withstand voltage test, the rated current loading test were conducted to confirm the soundness of cables and the stability of current loading. One of the characteristic tests conducted this time is the current diversion test. Despite the six-year outage and the massive earthquake that occurred during that time, all tests confirmed that there was no deterioration in the performance of the cable system. In the current diversion test, it was confirmed that the current was evenly distributed to each conductor at the cable joint.

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.

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.

A Method to Quantify Technical-Economic Aspects of HTS Electric Power Cables

In prevision of an expansion in the installed power and the progressive increase in electrification toward energy transition, high-efficiency electric grids are required. In this process, superconducting power cables could play an important role as they can be installed either to realize new lines or to replace existing infrastructures, potentially reducing the costs and the environmental impact compared to conventional solutions. The technical-economic convenience of the superconducting choice depends on the design parameters of the line, such as the voltage and power levels and the line length. For each condition, the configuration of the cable and its cooling system must be optimized while complying with a number of electrical and geometrical constraints. Identifying a priori the optimal cable configuration is not trivial, as the numerous variables involved are mutually dependent. This article describes a novel tool developed to quantify technical-economic aspects of superconducting cables, allowing the user to freely select the operating conditions for a generic electric line. The tool adopts a genetic algorithm to solve a constrained minimization problem for a multivariable function, returning the cable configuration characterized by the lowest costs. For this study, ac concentric cables realized with high temperature superconductors are selected, but the approach described can easily be adapted to other types of cable. By means of suitable simplifying hypotheses, the equations used to size the cable components and their corresponding costs, estimate the thermal inputs and describe the cryogen flows are introduced as parametric equations. Finally, the results of a detailed study on the impact of the relevant parameters on the cable design and costs is provided.

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.

Experimental Evaluation of Dielectric Losses of PPLP for Single Phase HTS Cable at Subcooled LN2 Temperatures

For the operation of high-temperature superconducting (HTS) power cables in liquid nitrogen (LN2 ) at high voltage levels, there is a need for reliable and cost-effective insulating materials. This article investigates the dielectric losses in poly-propylene laminated paper (PPLP- Sumitomo) which is used as a cold dielectric for HTS cables. To calculate the dielectric losses, an experimental setup was developed to measure the relative permittivity of PPLP at different temperatures from 65 to 300 K at various frequencies. Using an in-house developed experimental setup, the dielectric loss for different layers of PPLP, at various temperatures and operating frequencies was estimated to evaluate one of the criteria of cold dielectric material and the same was compared with the data at room temperature. The temperature was reduced to 65 K using a vacuum pump-assisted sub-cooling system. The effective relative permittivity increases marginally for subcooled LN2 impregnated PPLP, however there is reduction in tan delta loss which in turn reduces the dielectric loss and is useful for high voltage HTS based AC cables. This paper provides a comparative study on PPLP performance variation with respect to operating temperature and frequency.

Superconducting liquid cryogen insulated power cables for medium voltage applications

Liquid Nitrogen (LN2) is used as the cryogen and is part of the dielectric insulation system in most high temperature superconducting (HTS) power cables. However, in electric propulsion systems for transportation, using LN2 is not feasible due to asphyxiation concerns in the event of a leak in a confined space. Gaseous helium (GHe) has been proposed as an alternate cryogen to relieve this asphyxiation concern. GHe has benefits such as a wider operating temperature range and versatility for a centralized cryogenic cooling system for multiple devices which could potentially reduce the overall weight of the superconducting system. The drawback is that GHe has a lower dielectric strength compared to LN2, which limits its use to low-medium voltage applications. A hybrid cryogen HTS cable was proposed using LN2 as the dielectric media and GHe as the cryogen of an HTS cable to solve the limitations and issues associated with each cryogen and explained in this paper. A 1-m prototype cable that used LN2 as the cryogen and dielectric was fabricated and dielectric breakdown measurements were performed on it to establish a baseline on what to be expected from the hybrid cryogen HTS cable.

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.

Development and testing of joints in high temperature superconducting power cable

Development and testing of joints in high temperature superconducting power cable

Preliminary Design of a Superconducting LVDC Power Cable for Tokamak Application

Tokamak device requires a very high current power supply from the local power distribution sources to the targeted magnets such as toroidal field (TF) coils and poloidal field (PF) coils. This paper presents a preliminary design of a 30-m/1-kV/10-kA low voltage direct current (LVDC) superconducting cable for the potential in Tokamak applications. The outer diameter of the DC cable is 122.41 mm, and the pressure drop of liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) in the inner and outer channels is about 6.59 kPa. The flow velocity of inner and outer LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> channels are 0.5 m/s and 0.25 m/s, respectively. The temperature rise of the entire cable was designed to be less than 5 K, which enhances the electricity supply safety and reliability. These preliminary design lays some technical bases for achieving high current and low loss power transmission. The designing results show that the LVDC superconducting cable has significant potentials for Tokamak applications compared with conventional copper cables.

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.

Mathematical Modeling and Current Characteristics Investigation of a 35 kV Three-in-One High Temperature Superconducting (HTS) Power Cable

Considering the lack of space resources limits the addition of conventional cables in urban centers, a three-in-one high temperature superconducting (HTS) cable, which has three separate superconducting cables inside a cryogenic pipe, can be used for urban power supply because of its small volume, large transmission power and low electromagnetic pollution. The three-in-one HTS cable gets a lot attention to be used for urban power supply nowadays. However, the uneven distribution of layer current in three-in-one superconducting cable is a challenge that it leads to the damage of superconducting tape, increasing losses and unstable performance. Therefore, applying an improved screening algorithm, a mathematical model is proposed and its calculation process is programmed in MATLAB for optimizing a 35 kV three-in-one superconducting cable to achieve the current sharing in the conducting layer of each phase. The resistance effect on each layer and the phase-to-phase distance influence on the layer current are considered when investigating the current carrying ability based on the numerical analysis model. Finally, a 35 kV/1 kA three-in-one high temperature superconducting cable short sample is constructed, and the current carrying operational performances of one of three-phase super-conducting cable are tested to verify the effectiveness of the optimization procedure.

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

Thermal and Electrical Characteristics of Hollow Former With Fault Current Limiting Function for Superconducting Power Cable

A superconducting fault current limiting cable (SFCLC) with a hollow former is composed of various elements with different electrical and thermal properties, including liquid nitrogen inside the former. This type of cable can be used to mitigate the impact of short-circuit faults. This paper introduces a computational model that combines thermal and electrical behavior to investigate the thermal and electrical characteristics of SFCLCs according to the composition of a hollow former. To verify the computational model, a superconducting power cable with a hollow former was fabricated and a fault current test was performed. Good agreement was obtained between the calculation results obtained from the proposed computational model and the fault current test results. In addition, using the proposed computational model, the relationship between increases in temperature and limitations on current was analyzed for each configuration of the former according to the length of the cable and the duration of the fault. The characteristic analysis provides information on the hollow former composition that most effectively limits the fault current, depending on the length of the cable and the duration of the fault. The results can be used to determine the material and dimension of the hollow former for SFCLCs design.