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.

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.

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 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.

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.

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.

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.

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.

In this master thesis, the design and implementation of a high-voltage switch using series-connected Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) is discussed. A high-voltage switch is needed for applications such as high-voltage DC converters. Multilevel modular converters (MMCs) can also aid in the voltage-blocking capabilities of converters. MMCs use multiple submodules to block the full voltage. Every submodule thus only blocks a part of the full voltage. Each submodule needs multiple components that can be expensive, like voltage sensors and gate drive circuitry. By having the submodules block a higher voltage, fewer components are needed. By implementing a higher voltage blocking switch into such a submodule, cost and components can be spared by having a lower total amount of submodules. Current technologies of high-voltage switches are MOSFETs, insulated gate bipolar transistors, thyristors or electro-mechanical switches. MOSFETs have the advantage of being faster and have lower losses than the other technologies. The downside of using MOSFETs is that the voltage-blocking capability is lower than the other technologies. This could be solved by connecting multiple MOSFETs in series for a higher blocking voltage. To do this, care has to be taken that the MOSFETs turn on- and off at the same time. They also need to share the voltage equally to take full advantage of the blocking voltage of each MOSFET. A cost-effective way to implement a high-voltage switch using series-connected MOSFETs is to use capacitive coupling. In this method, the gate charge needed to turn the MOSFETs on is stored in capacitors. When the first MOSFET is turned on, the other series-connected MOSFETs will also turn on. This method has the downside that the switch can only be turned on for a limited amount of time (a few microseconds) and that the voltage balancing is dependent on the load, the switching frequency and the parasitics of the circuit. For this reason, a single high-voltage MOSFET was used in this project, even though it can be slower and more lossy than the series-connected switch. An MMC submodule was made using a full-bridge configuration. Additionally required components such as a gate signal generator, power supply, voltage- and current sensors, and fault protection were also designed, built and tested. In this way, a functioning MMC submodule was created that can be used with a capacitor or an isolated transformer as its source.

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.

Emerging PV technologies like Perovskite has lead to the development of Perovskite/Silicon (Pvk/c-Si) tandem device (Multi-junction device) and has now gained a lot of momentum and attention due to the fact that the tandem device can reach a Shockley-Quisser limit of about 44.1% efficiency. But to speed up its development, a lot of emphasis is made on conducting tandem solar cell device simulations to have get a good idea on the experiments that can be carried out. Solar cell simulations for tandem devices are carried out in advanced 2D/3D solar cell simulators like SETFOS or Synopsys TCAD Sentaurus. These softwares have large computational time and have complex user interface making simulations challenging. There are 1D solar cell simulators like ASA (Advanced Semiconductor Analysis) developed at TU Delft that has less computational time with an easy and intuitive interface. But ASA does not have the appropriate tunnelling models to simulate the tunnel recombination junction characteristics of perovskite silicon tandem devices.

To make ASA a complete software suite for simulating perovskite silicon tandem device, tunnelling models proposed by Ieong et al. is used for both direct and band to band tunnelling. These tunnelling models use basic inputs like band energy data, electrostatic potential data and electric field data for a particular device and outputs the tunnelling generation rate that can simply be added to the continuity equations for electrons or holes during the simulation of the device. A fully fledged algorithm was designed for the automation of the direct tunnelling and the band to band tunnelling process with limited input from the user while using the models proposed by Ieong et al. In simple terms, the algorithm takes in the required input and scans through the device for every interface to check for tunnel contributions and performs calculations when necessary. All necessary conditions are included inside the algorithms to ensure that the simulation is accurately solved.

The validation of the newly developed tunnelling algorithm was commenced for PN junction, Silicon hetero-junction and finally the Perovskite-Silicon tandem device. The JV curve for the above device simulations with and without incorporated tunnelling models was extracted and a comparison was made with literature results and simulation results from other software suites. The newly developed tunnelling algorithms was concluded to be accurate. The JV curve obtained from the ASA simulation showed good agreement with literature results and simulation results from other software suites with error percentages of less than 3% for open circuit voltage, short circuit current and fill factor. With proper tuning of the device layer thickness, texturing on multiple layers for the tandem device and enhancing the mobility of the non-absorber layers for the perovskite top cell, further improvement can be expected in the simulation. These methods can eventually lead to reaching the Shockley Quisser limit of about 35.7% efficiency for the perovskite silicon tandem solar cell even when general opto-electrical losses are taken into account.

Energy consumption keeps increasing, and more than three-quarters of the EU’s green-house gas emissions stem from it. Hence, it is important to reduce or stop burning fossil fuels to limit the temperature rise to 1.5∘C according to the Paris agreement target. Nowadays, renewable energy sources and distributed generation are increasingly integrated into the electric power system to achieve the ambitious target of the energy transition. Renewable energy sources are inherently fluctuating in their power. Whereas the grid is stable. The interface between these two can be made smooth based on a medium-frequency DC-DC converter. The advantages of increasing frequency are high power density, significant weight and size reduction, dynamic power flow control, and power quality management. All these are possible mainly because of advancements in power electronics in the recent decade. However, these power electronics induce harmonics across insulations, which are fast rising voltages and are repetitive. The dielectric strength of insulations under these fast-rising pulses is to be understood. This thesis project studied oil impregnated paper behavior under pulsed stresses.

To test the Oil Impregnated Paper samples, a source capable of generating repeating pulses with fast rising and lower overshoots is required. This source comprises an AC- DC converter that will power the H-bridge. The pulses from the H-bridge are then fed into a 1:50 pulse transformer to step up the voltage, which is then delivered across OIP (Oil Impregnated Papers) through test components that regulate the pulse’s rising time and overshoot. The process began with identifying critical factors to consider while developing a pulse generator. Following that, a random transformer prototype is created along with another transformer to extract the parameters, which are then modeled in the circuit simulator and COMSOL to predict the pulse. An algorithm was created to optimize the transformer design. Finally, this design method creates a pulse transformer that generates the necessary output.

The OIP samples are then tested at frequency 50𝑘𝐻𝑧 and at various voltages with a rise time 𝑇𝑟 ≈ 1.3𝜇 𝑠. A lifetime curve was obtained using the data of ageing tests at five field strengths. The results showed that the lifetime was reduced with the increase in frequency. At lower fields, a transition was seen, indicating a shift in the ageing process.

In this thesis, an algorithm that calculates the hosting capacity of independent PV, or EV charger systems was created. The hosting capacity is based on slow voltage variations and voltage unbalances caused by worst case PV generation and EV charging scenarios. The algorithm was run for four different commercial and industrial networks, and a range of network impedances. The outcome of the algorithm resulted into two figures for each of the networks, representing the possible installed capacity of PV and EV charger systems, respectively.

Conventional high voltage test sources, i.e., transformers (cascaded and resonant), impulse generators, and rectifier circuits generate 50 Hz/60 Hz sinusoidal, lightning and switching impulses, and DC respectively. For arbitrary wave shapes, function generator and HV amplifier setup are available up to 50 kV and few kHz signal bandwidths. Superimposed signals (impulses or transients on a sinusoidal or DC) are generated from a careful design of superposition of two voltage sources. The demand of these unconventional test sources is increasing as new electric stresses are introduced in the current electrical power network due to the rise of power electronics. This motivates the search for a novel high voltage test source which can generate arbitrary wave shapes with larger signal bandwidth at higher voltage level. Modular multilevel converter (MMC) topology is a promising solution for high power applications because of its high efficiency, modular structure, and reduced filter requirement. Hence, the idea of a MMC-based high voltage test source is proposed for arbitrary wave shape generation. Such a converter-based test source can also be adapted as a mobile test system for site acceptance and diagnostic testing and opens an entire new high voltage research area.

This master’s thesis demonstrates the proof of concept of a MMC-based high voltage test source using a mathematical and simulation model. The first step is to identify critical differences between existing MMC applications versus high voltage testing applications. Based on this analysis, control methodology and converter parameter design are adapted for high voltage testing application. Since a power electronic converter generates an output signal with harmonics, a filter is required to obtain a smooth signal that can be applied to the test objects. The quality of the generated signal is measured in terms of the peak value and the slope of the output voltage. Also, the protection system and DC source requirements are investigated briefly for a comprehensive picture of the MMC-based high voltage test system. The thesis demonstrates the feasibility of the MMC-based high voltage test source with a proof of principle on paper and with simulations. Recommendations are given for the next steps to realize a high voltage test source for arbitrary wave shape generation.

There is a rapid increase in the off-shore wind farms and the interconnection between countries which results in an increased energy transfer over longer distances. High voltage DC (HVDC) cables can transfer this energy in a reduced cost and efficient way in contrast with high voltage AC (HVAC) along with many other benefits. For the HVDC cables extruded cross linked polyethylene (XLPE) insulation is preferred over the mass impregnated paper oil cable due to advantages such as low costs, simplicity, no use of oil and high operating temperatures.
One of the main degradation mechanism for such insulation type is weak electrical conduction of charges due to the material conductivity. Due to a local inhomogeneity of the insulation the ow of these charges is non-uniform. This results in the charge owing inside of a region not equal to the charge owing out of that region which causes a local charge build up. These charges are known as space charges. These create region(s) of high electrical stress which can result in partial breakdown or in some cases complete breakdown of the insulation material as well. Hence, space charge accumulation in cable insulation material governs the failure behaviour and life time of the cable.
This thesis look into the possibility of carrying out an off-line space charge measurements for real-sized HVDC polymeric cable insulation samples using the electrostatic probe technique. The first objective is to develop a calibrated sample using which it is possible to carry out the space charge measurement. Secondly, the possibility to convert the measurements obtained from the sample into the space charge distribution is looked into. A calibrated sample (prototype) is prepared and both the objectives are evaluated using it.

The shifting of the European countries, including the Netherlands, towards an electricity production dominated by renewable energy sources to be (nearly 70%) by mid-century will have a significant impact on the frequency performance of electric networks. This would cause the level of grid inertia to be considerably reduced. From this perspective, I have been working with DNVGL for a period of 9 months on developing a dynamic power system model that provides the possibility of assessing the frequency performance of the Dutch electric network as part of the Synchronous Grid of Continental Europe. The main aim of this model is to consider the anticipated decrease in system inertia caused by the high penetration of renewables in a future situation.

The CIGRE B1 – B3.49 JWG defined a standardised 145 kV inner-cone GIS cable termination design. This standardisation allows the creation of new common interface insulators. This would eliminate the planning hurdles due to the fact that the cable system is not usually defined at the time of switchgear manufacture. The new design also requires a detailed study to find the relation between interfacial pressure and electrical performance of the epoxy/ silicon rubber interface.

The first step is to design and build a test setup to study the epoxy/ silicon rubber interface. Next, AC breakdown and lightning impulse tests are carried out. Additional AC breakdown testing with oil at the interface, defects on epoxy and heated samples are also carried out. The relation between interfacial pressure and electric field strength of the interface is found and documented. The effects of lubricant, defects and heat is used to further characterise the interface. Simultaneously, the silicon rubber is modelled using hyperelastic material modelling techniques.

The results from the tests and FEM models are used to propose two new designs of the 145 kV inner-cone GIS cable termination. The high repeatability of breakdown values and distinct features of this test setup have prompted the sharing of the experimental setup and results through an IEEE publication.

The load of the electric grid in increased by the connection of more renewable energy sources and less controlled power stations. The transmission operator has to decide where and when new overhead lines are required. However the operator can also chose to utilize existing lines more by increasing the transport capacity. This can be accomplished by applying dynamic line rating. In this case the conductor temperature and sag will increase but should not not violate the safety limits. Therefore a device can be installed on over-head lines to monitor the temperature and sag in real-time. Several devices are already manufactured and tested. However these devices require a reliable communication. In this thesis the feasibility and reliability of communication with Low Power Wide area Network (LoRaWAN) protocol in an overhead line environment is studied. The first objective is to determine the consequences of DLR on overhead lines. Second shielding of the electric and magnetic field in an overhead line is evaluated. Finally an antenna is chosen and a prototype is designed to evaluated its thermal behavior, low frequency magnetic shielding capabilities and communication feasibility and reliability. The first objective is to understand how the conductor temperature, the sag and magnetic field increases in respect to the transport capacity. The change in conductor temperature is examine by considering several heating gains and losses mechanisms. The sag is approached by a sagging and parabola curve to evaluate the decrease of distance to the ground. The maximum magnetic field is determined for close distances from the conductor.Two methods are examine to shield form the electric and magnetic field from the overhead lines. There-fore the materials copper, aluminum, steel and mu-metal are evaluated on their conductivity and permeability. The antenna is determined by comparing a dipole, loop and slot antenna on their complexity and expected radio noise interference. The prototype is exposed to a test setup in which the surface temperature, and magnetic field, is measured. The reliability of communication is evaluated by analyzing the amount of send and received packages.In case of an increased transport capacity the conductor temperature of an overhead line mostly increase by Joule heating. For a conductor temperature increase and concentrated weight the sag increases with negligible tents of centimeters. The maximum magnetic field was calculated and resulted in a required shielding effectiveness. The thickness of shield was determined for each material to reduce the magnetic field inside an enclosure. A slot antenna was designed and made in the prototype and compared with simulations in respect to the reflection coefficient. The surface temperature of the prototype did barely gain heat by the generated induced currents. However the prototype does reduce the magnetic field inside and confirms the theory of low frequency magnetic shielding. Furthermore the communication is tested and resulted in reliable data transfer in the case of a 0.5 cm distant from the conductor through which a current of 800 A flow. Furthermore corona discharges were generated up to 130 kV in which data still was transferred successfully