Thesis

Study of long-distance high-temperature superconductor cables for HVDC power transmission

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Awarding institution
  • University of Strathclyde
Date of award
  • 2025
Thesis identifier
  • T17210
Person Identifier (Local)
  • 202061878
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Department, School or Faculty
Abstract
  • The carbon neutrality goal of achieving net zero by 2050 has sparked significant interest in offshore wind farms. With offshore wind farms being installed from short distances to long distances away from the seashore, a submarine power transmission infrastructure is a necessity. Considering power cable length and low net effective losses, a high-voltage direct-current (HVDC) system has been chosen over HVAC. HVDC cables are considered to be made out of high-temperature superconductor (HTS) material. HTS power cables hold immense potential for efficient, low-loss, high-current-density, and compact power transmission. But, unlike copper/aluminium, the HTS material has a sharp transient behaviour as a function of the operating current, temperature, and magnetic field. However, the susceptibility of HTS cables to faults in the grid, resulting in quenching or permanent damage due to joule heating, poses a critical challenge to their real-world resilience. The main aim of this thesis is to study and evaluate the long-distance HTS subsea power cable for offshore to onshore power transmission along the radial and axial direction of the 2G HTS power cable in terms of electrical, thermal, hydraulic and quench characteristics during the normal and grid fault conditions. Prior to the installation of longdistance cable experiments and lab prototypes, modelling and simulation work is needed to predict cable behaviour. Furthermore, modelling the HTS power cable was necessary as part of enhancing cable performance and design. To tackle the problem described above, a computationally efficient high-fidelity model over the whole length of the cable was needed to understand HTS cable characteristics. The complex design of the superconductor power cable was modelled using Finite Element Method (FEM). However, for long-distance superconductor electrical-thermal-hydraulic studies, the FEM simulation involves a computational burden and for the electrical network, it is not suitable. Novel discretised electrical-thermal-hydraulic SIMSCAPE components with non-linear resistive behaviour dependent on current and temperature in MATLAB/SIMSCAPE software were modelled, partitioning the cable into discrete blocks to understand the temperature along the axial length and to determine the impact of transient conditions on a long-distance superconducting power cable in transmission. The model has the advantage of having the flexibility to change the fault location and cryocooler spacing length along the length of the cable, including the HTS and copper former and LN2 layers. The experiment measured the joint resistance of the tape incorporated into the model. This study is unique in that it is the first to look at 100 km long-distance HVDC subsea HTS for offshore to onshore grid use capable of transmitting more than 1 GW of power at 100 kV voltage and an ampacity of 10 kA. The primary technical challenges in modelling this long-distance HVDC subsea HTS cable are due to its non-linear resistive properties, which vary with temperature, current, and magnetic field. These variations result in the cable's electrical and thermal behaviour changes along its length, complicating accurate modelling. Distributed RLC network models are implemented using Simscape cable blocks to address these complexities. Each Simscape block includes thermal, electrical, and hydraulic parameters of respective cable layers, considering conduction, convection, radiation heat losses, non-linear resistance, critical current, and pressure drop and temperature. It allows the integration of cryocoolers at specific points along the cable. For this study, an HVDC HTS power cable was considered and modelled both as a lumped element and as a distributed element model with 100 elements to compare and evaluate the cable parameters along the length. The parameters include temperature distribution, resistance, critical current, current, and losses at different spots throughout the length of the cable. To simulate the transient condition, a pole-to-ground (PG) 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 has been evaluated and presented. This research is the first to develop a 2D T-A of a subsea HTS cable with a 10-kA transport current to investigate the electromagnetic behaviour of the superconductor and the impact of the harmonics generated in the AC/DC converters on the cable. The crosssectional area of the HTS cable was modelled in 2D using COMSOL Multiphysics to examine harmonic ripple losses in the cable. These findings were further validated through experimental investigations on the superconductor tapes. This study underscores the benefits of integrating Superconducting Fault Current Limiters (SFCL) with HTS cables in the network, showcasing load sharing between the superconductor and copper former during steady and transient state operations, HTS quench and recovery time.
Advisor / supervisor
  • Yuan, Weijia
  • Zhang, Min
Resource Type
DOI
Date Created
  • 2024
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