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.

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.

The worldwide demand for electricity, which is steadily increasing, leads to a continuous need for developing and extending the electrical transmission networks. However, the installation of new overhead lines (OHL) faces many challenges due to societal and environmental reasons. One solution that gains widespread public support is the installation of EHV AC XLPE underground cables (UGC). Although this development is quite encouraging from a societal perspective, new challenges might arise, mainly from a technical perspective. This is due to different electrical characteristics of underground cables compared to OHL as well as long repair time in the case of failure in cable systems. These aspects highlight the necessity of investigating power system technical performance issues related to application of EHV cables to prevent any unwanted condition in partially cabled grids. This paper, among various system operation issues, investigates optimum shunt compensation sizing, reliability analysis, and condition monitoring of EHV cable systems. Reactive power compensation by means of shunt reactors should be allocated for long cables to consume their reactive power surplus. It is crucial to have sufficient size of shunt compensation because both undercompensation and overcompensation can lead to undesirable system operation like overvoltage and zero-missing phenomenon. In this work, the shunt compensation sizing of a 80 km double-circuit connection in the Dutch transmission system consisting of series connected OHL and cable sections is studied. The sizing is performed for two load-flow scenarios and based on four sizing criteria and different cable lengths in the case study. Moreover, the most decisive sizing criterion in each case is determined too. The next studied issue is the reliability analysis of partially cabled EHV grids. The additional components of UGC (joints and terminations) together with a significantly larger repair time (compared to OHL), reduce the reliability of the whole system. In this work, a reliability assessment approach is developed in order to examine how the installation of EHV UGC in transmission networks impacts the overall reliability level. A contingency analysis regarding failures of 380 kV OHL and UGC is performed through state enumeration. Reliability indicators are calculated by performing a dc load-flow calculation and applying remedial actions (if necessary) to relieve overloads. Varying cable length is installed in three connections in the Dutch network, the probability of load curtailment is calculated and the main factors that influence the probability of overload with EHV UGC are explored. The third studied aspect is the condition monitoring of cable systems. An advanced real time Condition Monitoring System (CMS) was installed in the Dutch 380 kV grid and its goal is to monitor the status of the cable connection and its impact on the 380 kV electricity transmission network. In this paper, a first comparison between measurement and simulation results, in both time and frequency domain, is presented. In this way a first validation of the simulation models is performed and the reasons of possible deviations are discussed.