In this thesis, we evaluate the statistical procedure based on the similarity index proposed by Ypma and Ross in 'Determing the similarity between expected and observed ageing behavior'. The function for the similarity index is defined based on the inner product of two probability density functions, assumed to be related to the Weibull distribution. The evaluated statistical test aims to verify whether an observation of censored lifetime data is compliant with a given reference distribution. The test is compared to both the likelihood ratio test and a test using a variation of the similarity index. The comparison between these tests is based on their power function. First, a clear explanation of the complete statistical procedure using the similarity index is provided. Then the observations for which the test can be used are explained further. Its application and small limitations are shown using an example. Then, the two alternative tests are introduced. This will be followed by a theoretical overview of the power comparison method. Finally, the simulation for the power comparison is conducted. The power function is estimated for multiple relevant base cases along a few alternative parameter lines. It can then be concluded that the likelihood ratio test has consistently higher power than the similarity index test. However, the variation of the similarity index demonstrates a varying power, with instances of both higher and lower values than the original similarity index test.

Since the introduction of SF6 in the 1950s, gas-insulated high voltage circuit breakers and Gas-insulated switchgear (GIS) have improved considerably, in particular concerning required drive energy for operation, compactness, and reliability. Nevertheless, high voltage insulation design has become increasingly challenging in recent years. Customer demands for reducing the physical footprint of HV equipment has led to an increase in operational field stress and therefore, much higher pressure on tolerances and increased susceptibility to defects. Dielectric design is based on how electrostatic fields are distributed and how much stress they can generate. In the course of conducting the intensive theoretical and experimental investigations on the dielectric design of insulation systems applied to high voltage power and pulsed power applications, it is becoming necessary to consider the influence of phenomena that have not been considered before. On top of that, as SF6 is one of the greenhouse gases listed in the Kyoto Protocol, SF6 usage regulations have been implemented in many industries. In Europe, SF6 is regulated under the F-Gas directive, which bans
or restricts its use for several purposes. Several studies have indicated that CO2 is a viable alternative to SF6 for the transmission and distribution of electricity.

In this context, this project aims to investigate a potential new phenomenon, the
occurrence of secondary discharges caused by propagating streamer or leader discharges in HV gas insulation. Learning more about such phenomena can help us improve the dielectric design or perhaps explain the occurrence of breakdowns reported in high voltage equipment for which no obvious cause could be found. Specifically, CO2/O2 mixtures will be studied, and its results compared to SF6. Breakdown in gaseous insulation is caused by propagating discharges that are external in ambient air, e.g. on a bushing, or inside high-pressure insulation, e.g. across the surface of a GIS insulator. During the propagation of such discharges and flashovers (streamer or leader), transient electric field enhancement may occur, leading the local fields to exceed the inception fields at other locations. This can result in secondary discharges.

Dielectric experiments using Image Intensifier and Photomultiplier tubes (PMT)
have been conducted at three different pressure ranges; SF6 and CO2/O2 were selected as the insulation mediums. A negative polarity electric field is expected to trigger the secondary discharge. An analysis of images obtained from optical investigations and time lag records obtained from PMT signals suggested that secondary discharges can occur at low pressures (0.2MPa) in both SF6 and CO2/O2. At higher pressures (0.4 to 0.6MPa), no secondary discharges were detected. The reason for this is that, at higher pressures, the breakdown field is higher leading to a faster propagation of discharge across that gap. Hence, the formative time lag of the discharge is very short (some 100푛푠 or less) and this short time is not sufficient for secondary discharge inception.

Revolutionary changes in automotive industry toward fully connected electrical vehicles is changing the world of Board Level Reliability (BLR) Vibration Testing. It is taking BLR Vibration tests beyond board level to board module application level.
In this thesis, it contains the development of a reliability test concept called Board Module level Vibration Testing that is required to cope with the challenging application driven requests.

In the transmission and distribution network of the future, there is expected to be a mix of both Alternating Current (AC) and Direct Current (DC). In the high voltage division owing to technical and economic aspects, there is a wider use of High Voltage Direct Current (HVDC) instead of High Voltage Alternating Current (HVAC). However, when observing the medium voltage network, it is noticed that it is completely AC in nature. One major reason for this preference of AC in the medium voltage network is the better know-how of an AC network and the presence of well established and reliable MVAC components and the ability to transform (step up and down) voltage in AC. A switch to Medium Voltage Direct Current (MVDC) is expected as the cost of power electronic components is decreasing with time, and there is an improvement in their performance. Therefore, switching to MVDC would provide advantages in the form of improved transfer capacity and better power control. MVDC grids are debated to be a vital member of the future distribution network. In the present scenario, there is an absence of such an MVDC grid. Thereby, there are also no MVDC accessories available which can be used in such a grid. Therefore, there is also the absence of a testing procedure for the same. CIGRE TB 496 provides the testing strategies for DC cable systems up to 500 kV, but it does not take into consideration the difference between an MVDC system and an HVDC system. The systems may have a striking difference in construction, such as concerning materials. Additionally, there is also a difference concerning max field stresses and thickness of the insulation. The possibility of using the AC accessories for DC application needs to be analysed, and it needs to be verified how such an AC accessory would behave under the influence of prolonged DC stresses. The use of existing MVAC accessories for DC would be beneficial given the high production standards and the voluminous supply chain of MVAC systems. Additionally, this also opens possibilities of reusing existing AC cable system for DC stress. It needs to be noticed that in DC, the field distribution would depend on the conductivity of the material which is different from AC where the field distribution depends on the permittivity of the material. The permittivity of insulation is virtually independent of the temperature. However, conductivity has a strong relation to temperature and electric field, which makes DC field distribution more complex when compared to AC field distribution for any geometry. The test criteria of MVAC and pre-qualification test for HVDC are well known and need to be utilised in proposing and motivating the test sequence and test voltages for the accessories to be used in the future MVDC network. These accessories to be used in this future MVDC cable system needs to be analysed using Finite Element Method (FEM). The field simulations would give identification of locations in the joint which are undergoing maximum stresses during DC application. These maximum values of stresses are used to calculate the voltage life of the system based on electro-thermal life laws. The test results based on the representative testing procedure would help in understanding the performance and lifetime of the cable systems under DC stress. Therefore, to understand all items previously mentioned, a representative testing procedure needs to be proposed and motivated to test the use of existing MVAC accessories in the future MVDC network.

Cable terminations are essential for connecting a cable to a piece of equipment such as a circuit breaker, transformer, motor, etc. Proper terminations are of great importance in order to provide faultless cable systems. Improper terminations could result in overheating, partial discharges, eventual breakdown, flashover and breakdown in the system. There are several defects that can take place in terminations because of environmental, ageing and imperfections caused during manufacturing and installation . A potential defect is the contamination of oil with water due to sealing failures.

Water contamination can lead to partial discharges that, when produced over the insulation result in accelerated ageing. Typically, online electrical measurements of partial discharges can be used for termination monitoring. However, online monitoring suffers from noise and interferences, and localisation of partial discharges can be a problem. To overcome the challenges of electrical measurements, optical means of detecting partial discharge is researched in this thesis. The main goal of the thesis is to study the feasibility of using the optical PD detection method in oil-filled cable termination. The aim was to detect surface discharges at the rubber-oil interface through an optical sensor.

The identification of parameters for selection and final choice of optical sensor for PD detection application were done. Various setups to produce the surface discharge at the rubber-oil interface were investigated and one of the method was finalized. The simultaneous measurements of PD with electrical and optical sensors were conducted in dry oil and oil with different moisture content. The analysis of data obtained from optical sensor in comparison with electrical sensor based on sensitivity, PD pulse, PRPD pattern and correlation factor are discussed. It is noted that most of the characteristics of optical measurements is comparable to the electrical measurements. Thus, it can be said that this thesis contributes towards initial step of using the optical PD detection for online monitoring of HV components.

The growing attention on renewable energy has already brought a rapid evolution in this field. As one of the most abundant energy on this planet, the solar energy starts to play an important role in the energy market. Various policies have already been proposed to encourage the renewable energy development. With the PV panels involved in the system, consumers can sell the extra energy from the PV panels' generation back to the grid, which makes them become prosumers. However, the PV panels generation cannot perfectly match the load peak, therefore, different power management methods are proposed to better schedule the power flow inside the grid-connected PV system. On the other hand, different tariff structures could also lead to the different energy bill. The prosumers also want to better allocate their load profiles to better suit for the tariff policies. Therefore, to find a suitable combination of power management method and electricity tariff are interested by prosumers.

This thesis aims at finding a suitable combination of power management method and electricity tariff for the prosumers based on the final energy bill. Four different power management methods are proposed to schedule the power flow inside the grid-connected PV system. The power flow data are simulated together with different tariff structures to calculate the final energy bill. A new method to generate the real-time electricity buy-in price is introduced, and four new feed-in tariff structures are designed with different compensation policies. Together with the power flow scheduled by power management methods, the final energy bill is calculated.

It is concluded that at least one of newly designed tariff structures can give a better or almost the same performance when compared with the existed tariff structures, and based on the final energy bill, a suitable combination of power management method and electricity tariff for prosumers can be found for the target countries/region.