For the future, several developments of the power system are expected. The transition towards a more sustainable energy supply puts new requirements on the design and operation of power systems, and the transmission network in particular. Offshore, a transmission grid will be implemented to collect large-scale wind energy and to interconnect national power systems. Onshore, the transmission network needs to be reinforced to transmit the large-scale renewable energy to the main load centers. As all these developments will impact the reliability of transmission networks, it is important to study and quantify these impacts in reliability analysis. Traditional overhead lines are facing more and more opposition from local society, such that underground extra-high voltage (EHV) cable connections become a promising alternative for future grid extension. As EHV underground cables are a relatively new technology, not much is known yet about their behavior in large transmission networks. Underground cable connections (consisting of cables, joints and terminations) are in general less reliable than traditional overhead lines, mainly because of their much longer repair time. This can negatively influence the reliability of the transmission network as well. In this thesis, the reliability of EHV underground cables and overhead lines are compared, from the level of individual connections to transmission network level. It is studied which factors are of influence and what measures can be taken to improve the reliability. For offshore grids, network redundancy is a topic of discussion. Implementing offshore redundancy can be costly, but no network redundancy might lead to large capacity outages when connecting large offshore wind farms. In this thesis, the reliability of various offshore configurations is compared and it is discussed what level of redundancy is the most optimal. The consequences of offshore network outages for the operation of the onshore power system are considered as well. Recommendations for the implementation of offshore redundancy are given. The studies in this thesis show the importance of an integrated reliability analysis, where network design and system operation are combined, to find the most optimal solution. Decisions on network design will have consequences for system operation and vice versa. The studies in this thesis show how the reliability of underground cables and offshore networks can be assessed, which factors are of influence and what measures can be taken to improve power system reliability in the future.@en

Recently, the installation of new overhead lines (OHLs) faces many challenges mainly due to social and environmental reasons. One solution with widespread public support is the installation of Extra High Voltage (EHV) AC XLPE Underground Cables (UGCs). Although it is encouraging from a social perspective, new challenges arise like concerns about the reliability impact. In this paper, an approach is developed, which examines how the installation of EHV UGCs influences the reliability of transmission networks. The approach accounts for short-term operational measures and calculates several reliability indicators. A numerical case study of the Dutch EHV transmission network is performed. Based on probabilistic sensitivity analysis, it is found that the most influencing factors on the indicators are the loading of the cable connection, the repair time and the cable configuration.@en

For the future, a large-scale expansion of offshore wind energy is expected in Europe. To collect this wind energy and to enable electricity trading between countries, an offshore network will be implemented in the North Sea. Maintaining a high level of security of supply at affordable costs is one of the key objectives in the design and operation of power systems and therefore, the reliability of offshore grids is an important topic of discussion. Whereas onshore, the security of supply is assured by reliability criteria like n-1 redundancy, the same n-1 redundancy might not be an economical solution for offshore networks. For todays (small) offshore networks, n-1 redundancy is hardly economically justifiable, seen from a wind farm owner's point of view. The question then arises how the reliability of large-scale offshore networks should be evaluated and what measures can be taken to maintain a high security of supply onshore. This paper aims at discussing this topic by reviewing the results of recent research work. It is found that whereas for smaller offshore networks reliability evaluation is mainly an economic analysis seen from a wind farm owner's point of view, for large-scale offshore networks, it is necessary to consider the interaction of offshore–onshore networks in reliability analysis. It is proposed to analyze the reliability of combined offshore–onshore power systems in an integrated approach, such that various (offshore and onshore) measures can be considered to find the most economical solution. This article is categorized under: Wind Power > Systems and Infrastructure Energy Infrastructure > Systems and Infrastructure Energy Systems Economics > Systems and Infrastructure.@en

Power systems throughout the world are experiencing increasing levels of power electronics interfaced generation in their generation portfolio. As these devices have a significantly different dynamic behavior than conventional synchronous generators, it is expected that this trend will pose power system stability related challenges. This paper presents the results of a questionnaire conducted within the MIGRATE project. The aim of this questionnaire, to which more than 20 European transmission system operators (TSOs) responded, was to identify and prioritize these challenges. The TSOs identified challenges related to rotor angle stability (two), frequency stability (three), voltage stability (five), and power electronics interactions and resonances (two). In a follow-up survey, the TSOs were asked to rank the challenges based on their severity, probability of occurrence, and time of manifestation. The decrease of inertia was ranked the highest among the 11 issues. Additionally, the TSOs gave insight into current practices with regards to system monitoring and analysis. Based on the ranking, mitigation measures are currently being designed in order to facilitate an even higher amount of power electronics interfaced renewable energy sources in the power system.@en

Power systems throughout the world are experiencing increasing levels of power electronics interfaced generation in their generation portfolio. As these devices have a significantly different dynamic behavior than conventional synchronous generators, it is expected that this trend will pose power system stability related challenges. This paper presents the results of a questionnaire conducted within the MIGRATE project. The aim of this questionnaire, to which more than 20 European transmission system operators (TSOs) responded, was to identify and prioritize these challenges. The TSOs identified challenges related to rotor angle stability (two), frequency stability (three), voltage stability (five), and power electronics interactions and resonances (two). In a follow-up survey, the TSOs were asked to rank the challenges based on their severity, probability of occurrence, and time of manifestation. The decrease of inertia was ranked the highest among the 11 issues. Additionally, the TSOs gave insight into current practices with regards to system monitoring and analysis. Based on the ranking, mitigation measures are currently being designed in order to facilitate an even higher amount of power electronics interfaced renewable energy sources in the power system.@en

Power systems throughout the world are experiencing increasing levels of power electronics interfaced generation in their generation portfolio. As these devices have a significantly different dynamic behavior than conventional synchronous generators, it is expected that this trend will pose power system stability related challenges. This paper presents the results of a questionnaire conducted within the MIGRATE project. The aim of this questionnaire, to which more than 20 European transmission system operators (TSOs) responded, was to identify and prioritize these challenges. The TSOs identified challenges related to rotor angle stability (two), frequency stability (three), voltage stability (five), and power electronics interactions and resonances (two). In a follow-up survey, the TSOs were asked to rank the challenges based on their severity, probability of occurrence, and time of manifestation. The decrease of inertia was ranked the highest among the 11 issues. Additionally, the TSOs gave insight into current practices with regards to system monitoring and analysis. Based on the ranking, mitigation measures are currently being designed in order to facilitate an even higher amount of power electronics interfaced renewable energy sources in the power system.@en

Power systems throughout the world are experiencing increasing levels of power electronics interfaced generation in their generation portfolio. As these devices have a significantly different dynamic behavior than conventional synchronous generators, it is expected that this trend will pose power system stability related challenges. This paper presents the results of a questionnaire conducted within the MIGRATE project. The aim of this questionnaire, to which more than 20 European transmission system operators (TSOs) responded, was to identify and prioritize these challenges. The TSOs identified challenges related to rotor angle stability (two), frequency stability (three), voltage stability (five), and power electronics interactions and resonances (two). In a follow-up survey, the TSOs were asked to rank the challenges based on their severity, probability of occurrence, and time of manifestation. The decrease of inertia was ranked the highest among the 11 issues. Additionally, the TSOs gave insight into current practices with regards to system monitoring and analysis. Based on the ranking, mitigation measures are currently being designed in order to facilitate an even higher amount of power electronics interfaced renewable energy sources in the power system.@en

In the planning and operation of power systems, actions are taken in different processes and time-horizons. The purpose of these actions is to secure a high reliability level. Although the three main processes (grid development, asset management, and system operation) are described in literature, there has been no explicit study on the time-horizons (long-term, mid-term, and short-term) and actual time-scale (decades, years, months, etc.) that these processes focus on. This study aims at making a review of the various activities performed by transmission system operators while reviewing the concept of each time-horizon and methodologies developed in literature. As decisions taken in different time-horizons can influence each other, the interactions and overlapping are discussed.@en

This textbook provides an introduction to probabilistic reliability analysis of power systems. It discusses a range of probabilistic methods used in reliability modelling of power system components, small systems and large systems. It also presents the benefits of probabilistic methods for modelling renewable energy sources. The textbook describes real-life studies, discussing practical examples and providing interesting problems, teaching students the methods in a thorough and hands-on way. The textbook has chapters dedicated to reliability models for components (reliability functions, component life cycle, two-state Markov model, stress-strength model), small systems (reliability networks, Markov models, fault/event tree analysis) and large systems (generation adequacy, state enumeration, Monte-Carlo simulation). Moreover, it contains chapters about probabilistic optimal power flow, the reliability of underground cables and cyber-physical power systems. After reading this book, engineering students will be able to apply various methods to model the reliability of power system components, smaller and larger systems. The textbook will be accessible to power engineering students, as well as students from mathematics, computer science, physics, mechanical engineering, policy & management, and will allow them to apply reliability analysis methods to their own areas of expertise. @en

This textbook provides an introduction to probabilistic reliability analysis of power systems. It discusses a range of probabilistic methods used in reliability modelling of power system components, small systems and large systems. It also presents the benefits of probabilistic methods for modelling renewable energy sources. The textbook describes real-life studies, discussing practical examples and providing interesting problems, teaching students the methods in a thorough and hands-on way. The textbook has chapters dedicated to reliability models for components (reliability functions, component life cycle, two-state Markov model, stress-strength model), small systems (reliability networks, Markov models, fault/event tree analysis) and large systems (generation adequacy, state enumeration, Monte-Carlo simulation). Moreover, it contains chapters about probabilistic optimal power flow, the reliability of underground cables and cyber-physical power systems. After reading this book, engineering students will be able to apply various methods to model the reliability of power system components, smaller and larger systems. The textbook will be accessible to power engineering students, as well as students from mathematics, computer science, physics, mechanical engineering, policy & management, and will allow them to apply reliability analysis methods to their own areas of expertise. @en

This paper investigates the viability of the integration of demand side response of large scale electrolyser facilities into electrical ancillary services markets. A review of the current structure and mechanisms of balancing markets, voltage control and congestion management in the Netherlands is presented, taking into consideration future market harmonization measures proposed by transmission system operators of central Europe. The conducted research includes the assessment of the technical adequacy of electrolysers with respect to existing prequalification requirements, as well as basic notions on the expected revenue from participation in these markets. Furthermore, to illustrate the value of electrolyser support for electrical networks, a case study derived from the predicted Groningen-Drenthe-Overijssel area for the year 2030 is developed. This section of the northern Dutch transmission grid includes the upcoming HVDC interconnection with Denmark (COBRAcable) and one of the largest offshore wind parks located in the North Sea (Gemini). Computer based simulations are performed with DIgSILENT PowerFactory. The obtained results highlight the potential benefits of electrolyser utilization@en

The increase in renewable energy sources in addition to the decrease in conventional synchronous generators is leading to significant challenges for the power system operators to maintain generation load balance and to manage the system's decreasing inertia. Proton Exchange Membrane (PEM) fuel cells are characterised by high current density and fast power injection, which makes them ideal for frequency containment. This paper presents a generic model for PEM fuel cells developed in PowerFactory for frequency stability studies and provides an evaluation of its performance in a reduced-size dynamic model of the North Netherlands high voltage transmission network. The results show that the PEM fuel cell provides improved frequency response within the containment period when compared with synchronous generators for the same amount of support reserve.@en

In the future energy system, hydrogen as an energy carrier will play a role of increasing importance. Electrical energy can be converted into hydrogen locally by electrolysers and stored for a relatively long period. Then, the hydrogen can be used by final consumers like the transportation system or industries, as conceptually illustrated in Fig. 1. The flexibility of electrolysers offers promising possibilities for electrical grid support by the provision of ancillary services. Currently, a pilot power-to-gas facility with a 1-MW electrolyser is installed in the northern part of the Netherlands. A larger electrolysis plant of 300 MW may be installed in this area later. The feasibility of this large-scale plant, its impact on the stability of the electrical transmission network and the possibilities for ancillary services provision are currently being investigated in the project TSO2020 [1].@en

Western Europe is heavily investing in offshore wind power, but the costs of these wind farms remain high. For that reason, current transmission grids for offshore wind energy are predominately radial to reduce investment cost. To date, selection approaches of offshore grid configurations are mainly based on the level of reliability. This paper introduces an alternative selection approach to comprehensively assess the net present value (NPV) of near-shore power grids. The assessment encompasses, among others, a load flow analysis, as well as the sensitivities to parameters like failure rates, repair times and energy prices, for different grid configurations (i.e. radial/ meshed). A case study of the Dutch offshore transmission system shows that this approach helps in finding a suitable tradeoff between lowest feasible NPV, while also improving the reliability (in terms of reduced lost energy) of the offshore grid. @en

In this paper, three topologies of transmission grids in the North Sea with different feasible structures for scenario 2030 are defined. Each of these topologies is optimized towards the objective of minimum total cost (i.e.The sum of investment and operational costs, including the costs of fuel, CO2 emission and load shedding, throughout the lifetime). The topologies are compared through a cost benefit analysis within the scope of six countries surrounding the North Sea. Sensitivity analysis is performed to investigate the implications of each topology against a wide range of uncertainties. As a result, the optimized North Sea Infrastructure in a hub-And-spoke structure with the North Sea Wind Power Hub located at the Dogger Bank leads to the lowest total cost among all compared topologies.@en

In this paper, three topologies of transmission grids in the North Sea with different feasible structures for scenario 2030 are defined. Each of these topologies is optimized towards the objective of minimum total cost (i.e.The sum of investment and operational costs, including the costs of fuel, CO2 emission and load shedding, throughout the lifetime). The topologies are compared through a cost benefit analysis within the scope of six countries surrounding the North Sea. Sensitivity analysis is performed to investigate the implications of each topology against a wide range of uncertainties. As a result, the optimized North Sea Infrastructure in a hub-And-spoke structure with the North Sea Wind Power Hub located at the Dogger Bank leads to the lowest total cost among all compared topologies.@en

Hydrogen as an energy carrier holds promising potential for future power systems. An excess of electrical power from renewables can be stored as hydrogen, which can be used at a later moment by industries, households or the transportation system. The stability of the power system could also benefit from electrolysers as these have the potential to participate in frequency and voltage support. Although some electrical models of small electrolysers exist, practical models of large electrolysers have not been described in literature yet. In this publication, a generic electrolyser model is developed in RSCAD, to be used in real-time simulations on the real-time digital simulator. This model has been validated against field measurements of a 1 MW pilot electrolyser installed in the northern part of The Netherlands. To study the impact of electrolysers on power system stability, various simulations have been performed. These simulations show that electrolysers have a positive effect on frequency stability, as electrolysers are able to respond faster to frequency deviations than conventional generators.@en

To prevent large blackouts, reliability analysis and reliability management are of the utmost importance. While deterministic approaches and criteria have been used effectively in the past, probabilistic methods will be increasingly applied in the future as these provide more insight into the reliability of the transmission network. This chapter describes how probabilistic reliability analysis is used to study the reliability of large transmission networks. The following are two methods for reliability analysis: state enumeration and Monte Carlo simulation. The chapter introduces the concept of time horizons in the planning and operation of a power system. Several reliability indicators are commonly used in probabilistic reliability analysis. The chapter discusses these indicators. These reliability indicators can be directly related to security‐of‐supply, but can also be additional reliability indicators. The chapter describes a case study of the Dutch transmission network.@en

A large integration of offshore wind power plants and the construction of an offshore transmission network is expected for the next years. This network is also expected to interconnect onshore transmission systems. A key question to this endeavour is whether this offshore network should be n-1 redundant like the onshore network, or whether the onshore power system is strong enough to cope with failures of the offshore network. To address this issue, this paper provides a comprehensive investigation on various possible causes of power imbalance, like generator failures, load/wind prediction errors and offshore network failures. General insight is obtained about which causes of imbalance are the most severe and whether n-1 redundancy is required in offshore networks. The main finding is that onshore reserve generation can serve as redundancy for the offshore network in the studied power system. Nevertheless, the determination of the level of offshore wind capacity until which this conclusion holds remains as an open research issue.@en