High Temperature Superconducting Power Cable Research Articles

Performance enhancements of HTS power cables by minimizing the electric field enhancements for electric transport applications

Abstract Design innovations to manage the electric field enhancements and successful use of cryogenic epoxy EP37 as electrical insulation for high temperature superconducting (HTS) cables for electric aircraft applications are reported. Detailed finite element analysis (FEA) of the electric field distribution shows that the highest electric field is at the interface of the ground and electrical insulation layers. The FEA led to the design, fabrication, and experimental characterization of four model cables with stress cones and a direct bond of the ground and insulation layers. Enhanced partial discharge inception voltage (PDIV) was achieved in the model cables by minimizing the electric field enhancements at the ground layer interface. Using a helium gas mixture with 4 mol% H2, with higher intrinsic dielectric strength than pure helium, further enhanced the PDIV. The results warrant further studies on long HTS cables with EP37 as electrical insulation with a direct bond between the insulation and ground layers.

Test Station for High Temperature Superconducting Power Cables

Test Station for High Temperature Superconducting Power Cables

Isolating electrical and cryogen flow for safe operation and design validation experimentation of HTS power cables for electric transportation

The need for protecting the cryogenic infrastructure during a fault in high-temperature superconducting (HTS) power distribution systems of electric transport platforms is highlighted. A dual grounding scheme with an isolator between the electrical and cryogen flow paths of HTS power cables is needed. Finite element analysis of the electric field distribution of the vacuum jacketed isolator showed electric field intensity at the triple points. The electric field intensity at the triple points is reasonable if high vacuum quality is maintained. There is a need for further investigations for design validation with experimentation of practical designs for effective isolation and protection of cryogenic infrastructure from damage during an electrical fault in a section of the power distribution network of electrical transport platforms, such as an electric aircraft or ship.

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

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.

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.

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.

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.

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.

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.

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.

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

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

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.