Heavy industry is responsible for about a third of global emissions but lags behind in its effort to become carbon neutral. The electrification of industrial processes is a necessary step to achieve this goal. The asphalt industry is a good candidate for decarbonisation, as it currently relies on burning fossil fuels to heat and dry the aggregate used in asphalt production. Instead, aggregates could be heated electrically by using induction heating.

This thesis will investigate the design of an aggregate induction drum heater. A COMSOL model will be developed to aid the design process and predict the heater behaviour. The heater will be powered by a resonant converter, which is modelled in Simulink. A test setup is built to serve as a proof-of-concept for the design and to experimentally verify the models.

The analysis of the simulation and test results show that the model quality is dependent on the description of the material properties. The COMSOL model predicts the temperature of the middle of the heater with reasonable accuracy while the Simulink model is able to simulate the coil current and converter voltage waveforms with little error. The design of the aggregate induction heater could be improved by thermally insulating the outside surface and increasing the contact area between the aggregate and the heater.

This thesis investigates the design, analysis and testing of medium-voltage planar transformers for modular Solid State Transformer applications, with a particular emphasis on insulation for medium-voltage level. The renewable energy and microgrid implementation in the generation and distribution segments of power grids is motivated by the global urgency of the energy transition, particularly in response to the challenges in the Netherlands related to the phase-out of natural gas and grid congestion. Central to this work is the development of modular Solid State Transformers (SSTs) tailored for microgrid applications which are one of key components in the transition to more sustainable energy, for which planar transformers in high-frequency operations have to be designed.

A thorough review of high-voltage planar transformer design is conducted, focusing on core and winding losses, parasitic elements, and the complexities of achieving sufficient insulation within compact designs. The thesis outlines the design of a high-frequency planar transformer optimized for modular SSTs, highlighting key aspects such as core selection, loss minimization, and insulation design. Simulations are performed to assess the impact of high-frequency effects on transformer performance, with particular attention to the optimization of winding and shield configurations for improved field distribution and reliable insulation.

Multiple critical aspects in the design of insulation are pointed out and the experimental work is dedicated to testing these aspects.The PCB-based insulation under high-voltage conditions, with a focus on partial discharges and breakdown voltage in scenarios involving parallel conductors within a PCB layer. The results demonstrate the robustness of PCB insulation while revealing challenges posed by surface discharges and the effects of external conditions such as oil and air. These findings provide critical insights into the dielectric performance of FR4 laminates, contributing to the enhancement of insulation system reliability in planar transformers.

The outcomes of this research offer valuable contributions to the design and optimization of high-voltage planar transformers, underscoring the importance of balancing compactness, efficiency, and reliability. These advancements are essential for the development of resilient and sustainable energy systems in the context of the global energy transition.

The world is currently undergoing an unprecedented energy transition from fossil fuel-based energy sources to renewable energy sources. Additionally, advancements in power electronics technology have made High Voltage DC (HVDC) the most cost-effective method for long-distance electrical power transmission over both sea and land. These developments have led to an increased presence of Power Electronic Interfaces (PEIs) in the electricity grid. The insulation of High Voltage (HV) equipment in the electrical power grid is subjected to various electrical stresses due to the solid-state switching of PEIs. This can weaken the dielectric material of the HV equipment and therefore reduce the reliability of the electrical power system. Conventional test sources cannot replicate complex waveforms. Therefore, it is necessary to develop an Arbitrary Waveform Generator (AWG) capable of testing HV equipment with complex waveform shapes. A Modular Multilevel Converter (MMC) is a promising topology for this purpose, where each submodule (SM) requires auxiliary power to supply the Gate Drive Units (GDUs) and Distributed Control Units (DCUs). The objective of this thesis is to design the Auxiliary Power Supply (APS).

This thesis proposes using a flyback-based Input Series Converter as an APS. The proposed converter offers advantages such as integrated active Input Voltage Sharing (IVS), a scalable design, wide-input operation, and a minimal component count. The proposed converter topology is compared with other topologies discussed in the literature through SPICE simulations. Furthermore, various synchronous switch driving methodologies are studied and compared, given the necessity of series-connected switches with the currently available devices on the market.

A critical aspect of the design of a flyback-based Input Series Converter is the multi-winding transformer; hence, this thesis places special emphasis on the electrical and mechanical design of the flyback transformer. The transformer provides HV insulation between the SM capacitor and the output of the APS, as well as active IVS for balancing the voltage across the input stage capacitors and the MOSFETs. A prototype of the multi-winding transformer has been developed and used to assemble an open-loop converter. The converter's performance is tested with an input voltage range of 300V–3600V, and the design is further refined with an output diode snubber circuit.

A scalable, compact, and reliable topology has been identified for an HV-wide input APS for an MMC-based AWG. The topology provides suitable HV isolation between the SM capacitor and the APS output, as well as between the gate pulse generator circuit and the APS power stage. However, the transformer winding design led to a mismatch in leakage inductance between the different converter primary side stages. This resulted in a slight discrepancy in the voltage shared between the series-connected MOSFETs during the converter's turn-off stage. Future work should focus on employing a winding design that ensures equal coupling of all primary windings to the secondary winding in the flyback transformer. Additionally, it is recommended to use a coupled inductor-based passive LC snubber rather than an RCD snubber across the primary windings to introduce an active IVS process during the turn-off stage of the converter as well.

One fifth of the global carbon dioxide (CO2) emissions can be attributed to the transportation sector. Consequently, the growing desire to participate in the energy transition begs for the exploration of alternative modes of transportation. This endeavor is particularly challenging in the field of aviation and aircraft propulsion, where the injection of electrification and electric motors (EMs) pose many hardships such as the need for high autonomy, light weight, high power density and reliability. This work will mainly focus on the latter.

Unlike the low voltage machines used in road mobility, the motors necessary to propel an airplane demand substantially higher voltages due to their power requirements. Despite the availability of dielectric materials and insulation techniques, an improper design of the insulation system may make it susceptible to electrical stress, possibly reaching its breakdown voltage, generating partial discharges (PDs) and degrading the insulating material overtime. This will eventually lead to the electrical failure of the machine.

This danger is further increased by the recent rise in popularity of new wide-band gap power electronic devices. These devices offer many advantages: reduced size and weight, the ability to operate in higher temperatures, and the improved efficiency due to the reduction in power losses, caused by their steep switching speed in the order of 10−100 ns. However, the steep voltage transients (dv/dt) they produce create harmful side-effects to the machine. Firstly, the feeder cable connecting the voltage inverter to the machine terminals suffers Reflected Wave Phenomenon (RWP), where the voltage pulses are reflected at both ends of the line generating intereferences, which in turn generate overvoltages that can rise to up to twice the original voltage pulse. Secondly, the inherent leakage capacitance between the cable turns and the core of the stator slots produce an uneven voltage distribution along the wiring turns. These effects could increase the voltage stress in the insulator and momentarily reach the breakdown voltage in certain points of the geometry, producing Partial Discharges (PDs) that degrade the insulation over time.

To avoid this degradation, the aim of this thesis is to study these harmful effects in depth, back-up the literature review with accurate simulations and experimentation and realize the worst case scenario considering the geometry of a given motor that is currently under design. Once the phenomena is understood, some mitigation techniques are proposed to lower the chance of any discharge occurring.

This thesis investigates the impact of geometric, material, and operational parameters on the electromagnetic fields (EMFs) emitted by submarine power cables, particularly those used for offshore wind power transmission. The study is essential due to the growing deployment of offshore wind farms and the corresponding need for efficient submarine power transmission systems, combined with ecological concerns. The primary focus is on high-voltage alternating current (HVAC) cables, commonly used to connect offshore wind farms to the onshore grid. The rapid expansion of offshore wind power has highlighted significant ecological and environmental concerns, especially the effects of EMFs on marine life. Species such as elasmobranchs (sharks, rays, and skates) are highly sensitive to EMFs, making this an important area of research. The objective of this thesis is to develop guidelines for modeling EMFs from submarine power cables to aid ecological research, focusing on establishing effective parameters for EMF emission models. A literature review has shown that EMFs can impact marine animals’ navigation, predator-prey relationships, and embryo- genic development. Elasmobranchs, in particular, are vulnerable due to their sensitivity to EMFs. The review highlights the necessary accuracy levels for EMF models, focusing on HVAC cables. Starting with the basic physics including Maxwell’s equations, the Biot-Savart law, and the Lorentz force, followed by an outline of HVAC cable and transmission system design parameters, an understanding was created of the electromagnetic phenomena occurring in a submarine power cable. It was concluded that modeling EMFs requires considering current distribution along the conductor and metallic sheath, and the local interactions between cable components that result in shielding of the EMFs. A method from literature was used for predicting the longitudinal distribution of current along the conductor. The current distribution was affected by voltage and current transmission requirements, impedance, and the capacitive and inductive properties of the phases as well as reactive power compensation. Analyzing these parameters showed that all are crucial for accurate EMF modeling, as parameter changes within realistic ranges could result in differences over 10%. A significant part of this thesis examines the intensity of the metallic sheath currents. Modern HVAC cable designs use conductive polyethylene layers around the metallic sheaths, creating an electrical interface between them. This was conventionally assumed to dissipate circulating currents in the sheath, but this thesis questioned this belief. It was proven that some circulating currents remain and that induced currents were even unaffected by the conductive interface. The induced currents in the metallic sheath are shown to only be influenced by the conduction current and its design parameters, inductance, and resistance per unit length. Testing on the Borssele Alpha cable showed that sheath current for all standard operations was more than 12% of the conduction current. An analysis of the local impact of various design and operational parameters on EMF emissions was conducted using COMSOL Multiphysics. The Borssele Alpha 1 cable design served as a standard test case. The analysis highlighted the importance of the metallic sheath and even more so, the armor layer. The steel armor layer created a path of low reluctance, with geometric parameters and permeability playing significant roles. The effect of twist in the phases and armor wires on field emissions was also shown. The lay-length of the phases played a large role due to its effect on destructive interference between emissions of different phases. The armor lay-length had a considerable impact as well, possibly affecting the reluctance of the armor layer. The parameter analysis also confirmed the validity of an ultra-shortened section length in COMSOL, greatly reducing simulation time without impacting results. This research provides insights for developing accurate EMF emission predictions, aiding biologists and ecologists in evaluating the environmental impacts of offshore wind power infrastructure. This can guide the development of mitigation strategies and support sustainable expansion of renewable energy sources. Recommendations for future research include experimental testing of the sheath current model, further development of the transmission line method for the metallic sheath and developing better mitigation strategies. Unrelated to the main question is that in thermal analysis of comparable submarine power cable designs, the induced current must be incorporated, as it was unclear if this is the case. The findings of this thesis can significantly contribute to the sustainable growth of offshore wind power by addressing ecological concerns and improving the understanding of EMF effects on marine life.

The thermal rating of power cables is a critical aspect of electrical cable design that determines their safe operational limits. Traditional rating methods rely on worst-case assumptions for weather conditions, such as constant ambient temperatures or steady-state loading with a 100% load factor. Given the significant thermal masses and variations in ambient conditions, these assumptions often do not reflect actual operational scenarios. As the integration of fluctuating renewable energy sources into power systems increases, the dynamic nature of these systems becomes more pronounced. Consequently, the thermal rating of the power cables must be considered dynamic to accommodate these changing conditions. In this thesis, an improvement of dynamic cyclic rating predictions is explored for cable temperatures using the Finite Element Method (FEM). This improvement is performed by incorporating detailed weather and environmental data into the model. The study begins with a comprehensive literature review that provides an overview of existing dynamic rating systems and their applications. Subsequently, an analytical and numerical thermal model was developed and compared with COMSOL and CIGRE standards. It is concluded that the developed numerical model demonstrates greater accuracy and usefulness. This numerical model is integrated into a web-based tool called Ampwise, which serves as the basis for all future improvements. Cable data from the Windpark Fryslân project is used to validate the predicted temperature against the measured cable temperature. The research demonstrates that incorporating weather data significantly improves the precision of dynamic cyclic ratings, especially the inclusion of the real external air temperature and solar radiation of the location. Validation of the predicted conductor temperatures against measured DTS cable temperatures from the Windpark Fryslân project showed a mean absolute error (MAE) of 1.9 °C and a root mean square error (RMSE) of 2.3 °C. These results show the enhanced accuracy and reliability of the dynamic cyclic ratings when real weather data are incorporated. However, the rate of change in the real temperature is significantly higher than the predicted temperature, leading to short-term differences between the predicted and actual temperatures. In addition, a sensitivity analysis is conducted to assess the impact of various factors. The analysis highlights the importance of correct initial conditions, particularly ground temperature gradients and seasonal environmental variations. The thesis concludes that integrating weather and environmental data into dynamic rating models is crucial to achieving reliable and precise cable performance predictions over an extended period, thus supporting better operational decisions and infrastructure management.

Unwanted breakdown of insulation is one of the primary challenges affecting the reliability of power systems. Liquid insulation is commonly used in power grids and subsea installations due to its preferred qualities, such as heat transfer and safety. Some insulating liquids have been available since the earliest times, and some have been proven to be harmful to humans, animals, and the environment. Consequently, the search for better candidates has always been ongoing. Unfortunately, the knowledge of the quality of the insulating liquids is insufficient since numerous phenomena related to electrical discharge and breakdown in insulating liquids happen unexpectedly, often surprising the personnel involved. Therefore, gaining a deep understanding of the breakdown physics of these liquids and mechanisms leading to the degradation of their dielectric properties is crucial. This understanding ensures that the new replacements are suitable for specific equipment. Partial discharge (PD), as one of the initial stages before breakdown and a major player in ageing the insulators, is the main focus of this work. One way to monitor a liquid’s insulation quality is through the Partial Discharge Inception Voltage (PDIV)
level. Based on PDIV measurements, there are defined standards, such as IEC 61294. This work is focused on investigating the behavior of different types of liquids under the AC voltage stress above and below the PDIV level to determine if the defined standards reflect the dielectric characteristics of each liquid properly. Three liquids have been examined, including two candidates from commonly used insulating liquids in electrical installations. Tests are performed in a needle-plane geometry under high-voltage AC stress. The same liquids and geometry have been used multiple times in previous studies under lower frequency AC voltage, yielding unexpected results. Therefore, this study aims to investigate deeper by testing the liquids at higher frequencies and comparing observations with previous results. The experimental setup used for this work includes a 20 kV resonance voltage source, and the needle-plane gap distance is 20 mm. The current flow from the plane to the needle is mostly capacitive in the range up to 100 nA, but space charges are proved to play a major role in the conductive component of the current. PD behavior has been found to relate to molecular structure and, in some cases, to the previous stresses, likely due to residual ions remaining from previous cycles. The presence and nature of space charges have been investigated carefully by testing liquids at higher frequencies below and above the PDIV level. Further, the test setup was facilitated, and half-cycle voltages were applied to involve only one polarity of space charges, and the differences were observed. Another part of this work involved the optical PD measurement method, which utilized two photomultiplier tubes (PMTs) and a coincidence circuit to filter out ambient dark noise. This method was employed alongside the well-known charge acquisition method to detect the initial PD pulses in the liquid. The results demonstrated a noteworthy difference between the two methods, prompting further investigation.

This paper presents the design and development of an Electrical Discharge Machining (EDM) device aimed at achieving precise hole creation in diverse metal materials. The EDM device was conceptu- alized and constructed based on specific requirements identified by the group. The design process encompassed four main stages: dielectric fluid selection, electrode design, control system develop- ment and power supply. In the dielectric fluid stage, the importance and criteria for selecting an appropriate fluid were discussed, resulting in the choice of distilled water for its superior dielectric properties. The electrode design stage followed a similar methodology, leading to the selection of a copper rod as the optimal electrode material. The control system stage detailed the development of an open-loop, manual, and closed-loop control system, emphasizing the utilization of Klipper software for precise electrode control. The power supply section outlined three primary circuits: the power source, power amplification circuit, and square wave generator circuit. Detailed schematics, component justifications, and optimization values for key parameters were provided to enhance power supply efficiency. Experimental evaluation demonstrated the capability of the EDM device to effectively create holes in various metals using an open-loop control system. Additional experiments focused on parameter variations within the power supply setup further illustrated their impact on machining performance. The discussion highlights the challenges encountered throughout the project, particularly the constraints imposed by limited time, which prevented the realization of all initially set requirements. Despite these challenges, the EDM device successfully met most of the specified objectives, showcasing promising results for future refinements and applications in precision machining.

The goal of this project is to create a power supply for an electrical discharge machine (EDM). This machine can drill holes and create shapes in metal objects by evaporating material using discharges from the electrode to the workpiece. The electrode should be supplied with a high-voltage pulse wave in order to initate sparks. The power supply produces this waveform by turning a DC source on and off using a transistor as a switch. A current-limiting resistor that is placed between the source of the MOSFET and the electrode prevents short circuits during discharges. The circuit was first created with a DC voltage of 15V. A gate driver circuit to drive this MOSFET was designed to reduce power losses and to make the frequency and duty cycle adjustable. Then the design was improved by adding a diode to remove oscillations caused by the parasitic inductance of the power resistor. Afterwards, the circuit was built on a custom PCB to reduce parasitics. A filtering capacitor was added to remove high-frequency noise, after which a stable 15V pulse signal was obtained. A microcontroller is employed to regulate the pulse duration, detect spark occurrences, and relay this information to a speed regulator. This establishes a closed-loop system aimed at optimizing the overall system operation. To achieve this, circuitry is employed to convert the power supply output into a digital format, enabling the utilization of the microcontroller’s specialized hardware for rapid sampling.

In this thesis, "Design & Reliability Assessment of AEA Propulsion Grid", the development of a reliable and efficient propulsion grid for All-Electric Aircraft (AEA) is investigated to reduce aviation emissions. Our primary objective is to design a lightweight Power Management and Distribution (PMAD) system that meets stringent reliability standards. By analyzing materials, heat transfer, and grid design, we propose optimized grid topologies that balance weight and reliability. The findings emphasize the importance of redundancy and suggest further research into subcomponent failure rates, control aspects, and real-world testing to enhance system reliability and performance. This thesis provides valuable insights into the future of electric aviation, highlighting the necessity for continued investigation and practical application to ensure ultra-reliable electric propulsion systems and make zero-emission flight a reality.

As the need for both clean electricity and reduction of carbon emission rises, all-electric airplanes have the potential to reshape the field of aviational transport to fit this need. The development of such airplanes necessitates the advancement of highly reliable and efficient electrical systems, among which circuit breakers play a critical role. This paper investigates design considerations and challenges associated with circuit breakers for all-electric aircraft. The study explores possible circuit topologies that are capable to interrupt a 3 kV and 500 A power flow when a fault in the system causes a short circuit. Through simulations and experimental validations, the paper aims to propose an optimised circuit breaker design that enables reliable electric power systems in all-electric aircraft.

Abstract:

As grids become more and more saturated due to addition of more renewable energy sources in the system, the power demand keeps on increasing. This puts a pressure on the electrical utilities especially the power cables transferring power from one voltage level to another. Therefore, prior investigation into the effect of dynamic loading of such power cables is required before implementing the system in the physical grid.
One such saturated system is the implementation of offshore wind farm cables and the utilities connected to it.
The objective of this study was to check the effect of the dynamic nature of power flow through the connected cable system. In order to get a quantified result the degradation of the cable is measured in terms of the lifetime consumption of the cables under different loading schemes.
The offshore grid connection from Ijmuiden ver area in the North sea operated by Tennet has been identified as a case study for explaining the results. The offshore platforms are connected to the converter station with the help of 3-core 66kV HVAC cables. The connection from the converter station to the onshore grid is with the help of 2 525kV 1-core HVDC cables. The setup has been modelled with the help of two separate models for both the AC and DC cable sross-sections respectively. The models were developed in MATLAB (analytical) and Comsol Multiphysics
5.0 (numerical) to check the effect of dynamic loading of the cables with the help of different current vs. time profiles. The temperature variation with time was checked for the two cable systems.The parameters of soil thermal resistivity and the burial depth were varied from (0.2[W/mK],1200[mm]) to (0.36[W/mK],1500[mm]).
For the AC cable, it was observed that the lifetime consumption increases on changing the soil thermal conductivity and burial depth from 0.36[W/mK],1500[mm] to 0.2[W/mK],1200[mm]. The percentage lifetime consumption is dependent on the time duration for which the cable has been overloaded with a current value greater than the steady state value of 310[A] corresponding to 90◦C. The worst case change between the two cases was observed as going from 0.4439% to 0.5295% per year.Thus, showing that prior investigation is needed before loading the cable with a certain current profile under a given scenario.
For the AC case, on overloading the cable with a current value about 1.2 times the normal value, the maximum percentage lifetime consumption observed was 0.6208%. For the DC cable, the lifetime consumption was measured in terms of the time to failure of the insulation. This parameter is a function of the radial thickness of the insulation from the conductor screen to the insulation. The time to failure increases as one moves away from the conductor screen. Greater insulation deterioration was found to happen with the burial depth and soil thermal conductivity being (1200[mm],0.2[W/mK]) as compared to the case (1500[mm],0.36[W/mK]).A reversal in the
trend of time to failure was observed when the cable was overloaded with a current value of 1.2 times the normal current. The worst case mean value of time to failure observed was 39.68[y] for the normal case.

The integration of wind and solar energy through power electronic converters has introduced new challenges to High Voltage (HV) equipment in the electrical power system. Switchgear, cables, and transformers are now subject to higher dV/dt stress and complex wave shapes due to solid-state switching. This poses a threat to the reliability of the grid by weakening the dielectric material of these assets. Existing HV test sources face limitations in generating complex wave shapes and have restricted current capabilities. Building a customized test setup is time-consuming when combining multiple HV test sources for complex waveforms.

To overcome these challenges, an Arbitrary Wave shape Generator (AWG) for dielectric testing of HV grid assets is proposed. The Modular Multilevel Converter (MMC) topology is chosen for its modular structure, low harmonic content, and scalability to higher voltage levels. The initial focus is on dielectric testing of Medium Voltage (MV) class equipment, with the ultimate goal being the development of a modular prototype as part of a PhD project.

HV test requirements and procedures for conventional tests of MV class equipment are compiled, along with specifications for non-standard wave shapes in consideration of the hybrid grid. Two main HV test requirements are addressed in the PhD thesis: the output voltage range of 10 kV to 100 kV with a load capacitance range of 50 pF to 10 nF and a large-signal bandwidth up to 2.5 kHz. The second requirement involves generating steep pulses with a rise time of a few microseconds for a voltage magnitude of 250 kV across a capacitive load of 10 nF.

Despite the maturity of MMC technology for HVDC transmission, adapting it for HV AWG applications presents unique challenges. The thesis explores design trade-offs related to MMC parameters such as the number of Submodules (SMs) per arm, arm inductance, arm resistance, modulation technique, SM capacitance, and control system. Design criteria are developed and demonstrated through simulation models and a scaled-down prototype.

The control hardware of the HV AWG is addressed using a commercially available Real Time Simulator (RTS) named Typhoon-HIL. This choice is based on its flexibility to program arbitrary waveforms in the FPGA without coding in any special hardware description language. The performance is demonstrated in the scaled-down prototype, achieving sinusoidal waveforms up to 5 kHz reference frequency with THD less than 5%.

The second HV test requirement, steep pulse generation, is investigated with the MMC topology. It is found that the series-connected SMs of MMC make it challenging to obtain a short rise time across a large capacitive load. To address this, an integrated hybrid circuit of MMC and Marx generator circuit is proposed for complex waveforms with a rise time faster than 100 μs. Proper guidelines for choosing circuit parameters are provided and experimentally validated with a scaled-down prototype.@en

The integration of renewable energy systems into the grid brings new and unique propositions involving the integration of power electronic inverter based solutions into the High Voltage (HV) grid. Thus a need arises to test the HV components with unconventional waveforms which can be satisfied by the Arbitrary Waveshape Generator (AWG). Two such topologies have been shortlisted for the AWG, ie: Modular Multilevel Converter (MMC) & Cascaded H Bridge (CHB). The MMC requires a single insulated DC source while the CHB requires multiple insulated DC sources with isolation.

Developing insulated DC sources using traditional transformers requires oil, epoxy or other complex insulation materials. The insulation requirements are further exacerbated when HV > 5 kV is required at power levels greater than 1 kW. For this reason, Wireless Power Transfer methods are studied in this thesis to develop a DC Power Supply based on Inductive Power Transfer (IPT). The developed supply is capable of conducting DC breakdown tests and high frequency (>100 kHz) AC discharge tests on dielectrics.

The key requirements for developing such a system are Load Invariant Voltage, High Voltage Gain and Soft Switching. Considering these requirements the Series Parallel (S-P) topology is chosen to deliver 1.5 kW at a DC voltage of 5 kV from a 350 V input, with a diode rectifier. Using the Greinacher rectifier, 10 kV DC output is obtained. Different parameters of the developed resonant converter such as coupling coefficient, switching frequency, deadtime and overcurrent protection are analysed to find a suitable configuration for the DC Power Supply. An efficiency of 88% at rated load and load regulation of 18% is achieved for the developed power supply.

For the CHB, a multi-receiver IPT system is desirable to provide multiple isolated DC outputs. A 2-receiver and a 3-receiver IPT system is constructed and their coupling behaviour is studied. A conclusion is drawn that an ”n” receiver system has a coupling coefficient 𝑘𝑛 = √𝑛𝑘1 and accordingly a S-P IPT system can be developed to obtain multiple (n) isolated DC voltage sources.

The urgent need to decrease greenhouse gas emissions and enable clean energy transition has driven the power industry to seek compact and eco-friendly solutions for power transmission. Gas Insulated Switchgear has been a key technology in this regard, using Sulphur Hexafluoride gas as an insulating medium. However, is a potent greenhouse gas with high global warming potential, necessitating the search for more environmentally friendly alternatives.
Siemens Energy has proposed "Clean Air" as a substitute for inside high voltage. Clean Air, also called Synthetic Air is a homogeneous mixture of 80% N2 and 20% O2. However, due to its lower electrical strength compared to SF6, the GIS design with Synthetic Air as the insulation gas requires optimization and newer insulation techniques to maintain compactness and reliability.
The goal of this thesis is to analyse the breakdown strength of Synthetic Air as a substitute for SF6 inside the High Voltage GIS and examine the performance of its breakdown strength with dielectric coatings on the surface of the electrodes.
Initially, experimental studies were conducted to investigate the breakdown strength of Synthetic Air under various pressure ranges. Comparisons with compressed air reveal that Synthetic Air demonstrates similar electrical breakdown strength.
Next, the study focused on understanding the influence of dielectric coatings on the breakdown behavior of Synthetic Air for applications in GIS. Methodical optimization of coating thickness and air gap distance were done to effectively minimize the electric stress inside the air gap. The test setup was designed with electrodes coated with neat epoxy and the AC breakdown tests were performed. Compared to the uncoated electrodes, the coated electrodes showed significant improvement in breakdown strength.
Though the coated electrode did not breakdown at the voltage at which the uncoated electrodes broke down, with higher voltages, a new phenomena of surface flashover was observed. The observations of surface flashovers across the dielectric coatings demonstrated the ability of these flashovers to travel longer distances at remarkably low voltage ranges. This research concluded by postulating two hypotheses to explain the observed surface flashover phenomena. These hypotheses were researched and analyzed using FEM simulations and experimental investigations.

High Voltage (HV) power cables need to be connected to other HV equipment such as transformers or overhead lines. To safely connect the cable to such equipments a cable termination is used. The cable termination is usually filled with a type of dielectric fluid and is fitted and sealed at the customer site. However during the installation of the cable termination man made errors can occur and in some cases, it can result in ineffective sealing of the termination. These may act as points from where moisture or water droplets can enter inside the termination. The moisture which enters into the insulating oil would move towards the regions in the termination where there is high electrical stress due to the dipole nature of the water molecule. This area of high electrical stress is usually the surface of the stress cone. Depending on factors such as the amount of moisture entering the termination, it could take months or a few years to effect the functionality and eventual failure of the cable termination. The preliminary failure investigation shows evidence that the failure is caused to the stress cone, which is usually in contact with the mixture of water and the oil. The electrical activity on the surface of the stress cone due to the combined effect of the oil and water causes some discolouration and tracking of the rubber material. There are two main tests that are conducted in this research, one of the test is focused on the oxidation process of silicon rubber by thermal stress. The second test is a small scale test setup with oil and silicon rubber electrically stressed in presence of water to understand the long term effect on the surface of the material. Both the experiments conducted produced partial results which could be used to explain the degradation of silicon rubber, also information of partial discharge patterns which could be useful in detecting such moisture induced faults in terminations.

There has been significant research into the use of multilevel inverter topologies using Wide Band Gap (WBG) semiconductors in Electric Vehicle (EV) powertrains. This combination promises an increased power density and efficiency which should boost the viability and adoption of EVs. However, a reliable power supply is required for the inverter switches, which counters some of the challenges presented by these topologies. These challenges include the issue of high side power supply and Electromagnetic Interference (EMI) mitigation. To begin with, certain requirements for a high side power supply are drawn up and various architectures are compared based on their merits and demerits. Based on this comparison, the LLC resonant converter is chosen as the most suitable topology due to its high efficiency, power density and potential for EMI mitigation. The operating principles of this topology are examined and used to optimally design a one output LLC converter. These principles are then further extrapolated to the design of a LLC converter with six isolated outputs which are required for a multilevel converter. Both these designs are then prototyped and tested to verify their performance. It is found that the multi output converter performs at par or better than the commercially available solutions, while fulfilling the design requirements.

Remotely operated vehicles (ROV) are used for the inspection, maintenance and repair of submarine and offshore cables, subsea exploration, and rescue operations. ROVs are powered by umbilical cables, which have to withstand electrical, mechanical, and thermal stresses. This thesis investigates the effect of repetitive bending on the insulation properties of ROV umbilical cables for medium voltage.

Umbilical cables with XLPE, polypropylene, and HDPE insulation were mechanically aged using a cyclic bend-over-sheave setup, after which the dielectric properties were analysed using electrical breakdown tests and several diagnostic tests, such as partial discharge analysis.

The cables with XLPE and HDPE insulation showed delamination of the conductor–insulation interface, which resulted in increased partial discharge activity, a reduced breakdown voltage, and a significantly decreased lifetime. For HDPE, the lifetime power law exponent 𝑛 dropped from 18 to 9 after 23,000 cycles of mechanical ageing. Polypropylene, on the other hand, did not show delamination but an increase in dielectric-bounded cavities with mechanical ageing.

Insulated metal substrate (IMS) printed circuit boards (PCBs) are an attractive alternative to conventional FR4-based PCBs and power modules due to their good thermal performance, low cost, and compatibility with the reflow soldering processes. In this thesis, the dielectric performance of IMS PCBs is characterised to validate their use in high-voltage power electronic applications and ensure that an acceptable lifetime and reliability can be reached. In particular, the high-frequency degradation of the dielectric is investigated.

The IMS dielectric was characterised using breakdown tests with various voltage waveforms and frequencies to closely approximate their use-case in power electronic converters. Two high-voltage generators were designed and realised to generate high-frequency square-wave and sinusoidal waveforms. In addition, diagnostic tests were performed to identify the effect of electrical ageing on the dielectric properties.

he designed high-voltage test sources allowed for ramp breakdown and lifetime tests up to 100 kHz and 10 kVpk. These tests showed that the dielectric degrades extremely fast under high-frequency voltage stress, most likely due to localised high partial discharge activity and electrical treeing. As a result, no reasonable lifetime can be expected when operating above the discharge inception voltage. For thick dielectrics (>100 µm), surface discharges are the dominant degradation mechanism with an inception voltage of 2.4 kVpk. The maximum nominal voltage should be limited to approximately 1.5 kVpk to ensure the reliable operation of the IMS PCBs.