Bart W. Tuinema

Reliability evaluation of substations subject to protection system failures

In power systems, substations play a key role in connecting generation and load centers to the grid. Substations are also a critical building block in connecting large-scale offshore wind and submarine interconnectors to the onshore grid. Therefore, reliability evaluation of substations is of great significance. Currently, most of the studies related to substation reliability only consider the substation connectivity and ignore the effects of protection system failures, which is not realistic. In this paper, the reliability of high-voltage substations subject to protection system failures is analyzed using event tree analysis. For this analysis, actual failure statistics from the Dutch power system are used. The influence of different substation configurations on the overall substation reliability is studied. This provides valuable insight about the reliability of different substation configurations, which can be useful for designing substations in the future power system.

Reliability of Transmission Links Consisting of Overhead Lines and Underground Cables

Underground cables will be applied more often within new connections of the extra-high-voltage (EHV) transmission network. Since EHV underground cables are a relatively new technology, not much is known 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. It is therefore of interest to study the reliability of underground cable connections in detail. This paper concentrates on the reliability of EHV underground cable and overhead line connections. Based on actual failure statistics of individual components, the reliability of a connection is analyzed, and which factors are of influence and what measures can be taken to improve the reliability are studied. An optimized cable repair process and a configuration with additional disconnectors are two solutions.

Network redundancy versus generation reserve in combined onshore-offshore transmission networks

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.

Multi-parameter approach for the selection of preferred offshore power grids for wind energy

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.

Probabilistic reliability analysis of future power systems - survey and example

In the power system of the future, reliability will play an important role. This reliability is influenced by different developments like the increase in electricity consumption and the use of renewable and distributed generation. It is important to have a good insight into the reliability performance of the system. With probabilistic methods, the reliability of the power system can be analyzed and decisions can be made to maintain the high reliability level that we demand. This paper gives an overview of the different developments in power systems and describes how these developments influence the reliability of the future power system. The possibilities to implement these developments into the probabilistic reliability analysis in network planning and operational planning are discussed. By use of an example, the possibilities and challenges of probabilistic methods in operational planning are illustrated.

Reliability modeling of transmission networks: An explanatory study on further EHV underground cabling in the Netherlands

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.