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- PostWater Tree Mapping in Submarine High Voltage Cables Using Finite Element Method(2025) Ryeskog, Carl-Adam; Novljanin, Hazim; Chalmers tekniska högskola / Institutionen för elektroteknik; Serdyuk, Yuriy; Bordeori, Moon Moon; Li, ZhiyuanAbstract Water treeing is a degradation phenomenon that occurs in submarine power cables. It is one of the main causes of failures of dynamic cables attached to mobile floating platforms. The rough sea environment causes mechanical stresses in the insulation of dynamic cables provoking appearance of microscopic cracks and water intrusion. The combination of water and enhanced electric fields can cause electrical, chemical, and mechanical reactions to occur which intensify water tree growth in cable insulation. This thesis aims to contribute to the development of a numerical model for simulating water treeing in high voltage insulating materials. The scope of the thesis is limited to the electrical aspects of the water treeing. COMSOL Multiphysics is used to model the conditions for experimental water tree testing according to ASTM D6097 standard. The model considers the current flow in the polymeric insulation due to the applied electric stress and so-called state variable is used to map healthy and damaged regions in the insulation material. The latter is identified as a domain where the electric field exceeds the threshold corresponding to initiation of defects in the polymer due to appearing internal electrostatic forces. Validation is done by comparing the simulation to the standard and experiments reported in the literature. The results show that the numerical model follows previous observations and may be used as a base for further development of the tools for predicting insulation lifetime.
- PostDevelopment and Implementation of test cells to perform DC and LI breakdown testing of materials used in HVDC cable accessories(2025) Selvasekar , Nehru Selvan; Chalmers tekniska högskola / Institutionen för elektroteknik; Serdyuk, Yuriy; Nilsson, Susanne; Jafari, Sajad; Hussain, RashidAbstract The thesis work is to develop,build up and verify a test circuit for measurements of DC breakdown strength and LI testing. The work contains both practical and theoretical elements, focusing on optimizing the design of electrodes as well as the size and shape of samples and to determine the Optimal dielectric properties of the insulation test medium using COMSOL Multiphysics. The aim of the work is to develop methods and design test setups for measuring both DC breakdown strength and Lightning Impulse testing, as a function of electric fields. EPDM insulation and FGM are used in cable accessories considering EPDM rubber has low dielectric loss, making it ideal for high-voltage applications. FGM rubber can be produced by incorporating specific fillers and is designed to control and distribute electric fields within electrical insulation systems. Its main purpose is to prevent high electric field concentration, which can cause insulation breakdown and device failure.Rubber material is being tested using mechanical, chemical, and electrical methods. The dielectric test is one of the electrical testing methods used to determine the dielectric strength of rubber materials. Short-time and long-time tests are being carried out for dielectric testing. AC breakdown testing, DC breakdown testing, and LI breakdown testing on insulation EPDM and FGM samples are conducted using two different insulating liquids with variable permittivities to avoid surface flashover during a short test under international standards. Designing a test cell for a dielectric test with an applied voltage of up to 150kV. Design the test cell (CAD model) and choose the electric field simulation with COMSOL Multiphysics software. To enhance development, the molded electrode test setup has been designed to eliminate the influence of the surrounding medium and facilitate future endurance testing.
- PostDesign of smart orthosis for rehabilitation of Achilles tendon ruptures(2025) Anderson, Adam; Chalmers tekniska högskola / Institutionen för elektroteknik; Dean, Emmanuel; Brorsson, Annelie; Nilsson Helander, KatarinaAbstract This thesis presents a compact system for measuring forces under the foot, designed for rehabilitation after an Achilles tendon rupture. The aim is that this system could provide patients and care providers with critical data about the recovery process, for a more personalized and effective treatment. The core component of this system is a newly developed flexible insole that senses forces under the foot. The force is measured in three dimensions (i.e., normal and shear forces) using magnetic-based sensors, placed in a grid of 73 nodes. The large area covered by the sensor, and the flexibility, are improvements over previous magnetic-based force measurement systems. The insole and additional support electronics were mounted on a standard ankle orthosis (also known as Walker). In addition, two IMUs were used to estimate the orientation of the insole. Software was also developed to process and visualize the data. The measurements from the insole are sent to a signal processing chain to calculate relevant biomechanics parameters such as the center of pressure and joint torques. The signal processing chain was implemented within ROS2, together with micro-ros for the low-level communication with hardware. ROS2 is also used for visualization purposes. The results are promising, showing that magnetic-based sensors are feasible for measuring 3D forces under the foot. The sensors display a nearly linear response to vertical pressure, although there is considerable hysteresis that introduces errors in the measurements. Future work to improve calibration, verify reliability, and improve ease of use is needed before the system can be used in a clinical setting.
- PostAI for capacity estimation in overhead transmission lines - A new model proposal for deploying AI to do dynamic line rating(2024) Tydén, Ludvig; Nordin, Jonas; Chalmers tekniska högskola / Institutionen för elektroteknik; Le, Anh Tuan; Balouji, EbrahimAbstract Dynamic line rating (DLR) for overhead transmission lines, which estimates the current-carrying capacity based on environmental and operational conditions, presents an opportunity to enhance the efficiency and reliability of electrical grids. This thesis explores the feasibility and application of artificial intelligence (AI) to improve the accuracy and scalability of DLR systems, while also lowering the cost of installation. By leveraging machine learning models, particularly physics-informed neural networks (PINNs), this research aims to lay the foundation of the development of an advanced DLR solution capable of real-time and forecast estimation of the capacity of a transmission line. The initial phase of the thesis focuses on implementing a weather-based model, based on the IEEE-738 standard, to estimate line ratings based on weather parameters such as temperature, wind speed, wind angle and solar radiation, but also parameters such as the electrical current and conductor specific metrics. This model serves as both a practical tool for immediate deployment and a foundational step towards more complex AI models. Following the development of the weather-based model, the research transitions to the integration neural networks, with a perspective of utilizing physics informed neural networks. These models combine the data-driven capabilities of traditional machine learning with the robustness of physical laws governing power transmission. The objective is to enhance the precision and reliability of the DLR system, accommodating non-linear relationships and interactions within the data. The thesis proposes a new model of a DLR system based around the weather model and machine learning. The system consists of several modules that each serve a purpose, data collection, ML model, ML training, weather model and real-time capacity estimation. The findings demonstrate that AI-based DLR systems is a new, interesting approach that can significantly improve the operational efficiency of electrical grids by providing more accurate and adaptive line ratings. This research contributes to the field of power systems by offering a scalable and innovative approach to dynamic line rating, supporting the transition towards a smarter infrastructure. The project has gained interest from key stakeholders such as EON, Vattenfall, and Svenska kraftnät, and has been formed in close contact with their respective specialists in DLR systems. The involvement of these industry leaders underscores the practical relevance and potential impact of this type of research in this domain.
- PostTesting of Field Grading Materials For HVDC Cable Joints(2025) Kappadan, Sajil; Chalmers tekniska högskola / Institutionen för elektroteknik; Serdyuk, Yuriy; Nilsson, Susanne; Hussain, Rashid; Jafari, Sajjad; Hedlund, JennyAbstract HVDC cable systems are designed to transmit large amounts of electricity over long distances with minimal losses. Most failures in these systems happen because of issues with cable accessories like joints and terminations. They are caused by strong electric fields appearing in such components due to geometrical features of the designs and inhomogeneities in the structure of the insulation system incorporating various materials. To enhance the performance of cable accessories, electric field control in the insulation is crucial. To address this, so-called field grading materials (FGMs) can be used to even out the electric field distributions. Thanks to their non-linear properties, these materials secure normal operations of the cable system and also are capable of handling events like lightning overvoltage and switching impulses. This thesis focuses on exploring electrical and mechanical properties of FGMs by testing samples of materials with different types and concentration of fillers at various temperatures and electric field strength. The focus is on a comparative analysis, where the properties of EPDM (Ethylene Propylene Diene Monomer) are taken as a reference. New materials with good electrical and mechanical properties are selected based on specific criteria, followed by measurements of their non-linear conductivity. Experimental results show that three selected materials met the criteria for nonlinear conductivity. To further evaluate their performance as a base for building a large scale component, electrothermal simulations of a 525 kV DC cable joint made of those materials have been conducted for different voltage levels including nominal, type test and lightning impulse voltages. The simulation results show minimal differences in the field grading effects caused by the selected FGMs applied in different locations of the cable joint, likely because of similar non-linear behavior of their properties in the studied ranges of temperatures and electric stresses.