With the increasing requirements of the semiconductor industry, ASML lithographic machines, essential for chip manufacturing, are becoming more complex. Consequently, the mains distribution system, a crucial part of these machines, is increasingly vulnerable to short circuit (SC) faults due to the growing number of system components. SC assessment of this system in compliance with international standards is vital as they are utilized by companies worldwide.

This thesis provides a standardized assessment method for industrial mains distribution system that complies with international standards. The assessment method includes the determination of available SC current and overall short circuit current rating (SCCR) and is implemented as a Matlab tool. Additionally, this thesis explores ways to increase the SCCR of the system by improving protection and limiting current considering current-limiting alternating current circuit breakers and various direct current circuit breaker (DCCB) technologies, including fault current limiters. Finally, the assessment results are validated through the physical testing results of a branch circuit within the ASML mains distribution system.

This research aims to tackle the dual challenges of power electronic uncertainties and the intermittency of renewable energy sources by developing a comprehensive reliability model and conducting a probabilistic evaluation of VSC-MTDC-based hybrid AC/DC power systems. With a specific focus on the North Sea region, the study emphasises enhancing the reliability of these systems, which are increasingly utilised for the efficient transmission of offshore wind power. The objective is to optimise key factors such as redundancy, modularity, and maintenance costs, which are crucial for the reliable integration of these systems into existing power grids.

While Modular Multilevel Converters (MMCs) within these systems offer multiple advantages, the proliferation of power electronic components introduces substantial uncertainties, compounding reliability concerns alongside the inherent variability of renewable energy sources. To address these challenges, the proposed composite probabilistic models account for wind speed variability, turbine drivetrain reliability, and the stochastic behaviour of component failures, providing a detailed reliability model.

The findings highlight substantial opportunities for improving system performance through targeted design and maintenance strategies. By investigating the reliability of offshore wind power, MMCs, DC transmission system and the overall AC/DC system, this research provides valuable insights into optimising system performance and ensuring the efficient integration of renewable energy. The research outcomes include a composite (generation and transmission) model, reliability and cost assessment, an optimal cost-reliability strategy for MMC systems, and a constant risk-minimised cost method of substituting conventional generators with offshore wind power contributing to more resilient and cost-effective renewable energy integration.

The outcomes of this study provide crucial insights into enhancing methods for the reliability of hybrid AC/DC systems. The methodologies and results not only align with global sustainability goals but also bolster energy security by laying a strong foundation for future power grid designs that increasingly depend on sustainable energy sources and advanced power electronics.

\textbf{Keywords:} Adequacy, composite power system, multi-state model, offshore wind power, power electronics, reliability evaluation, VSC-MTDC