Reliability modelling in transmission networks: An exploratory study for further EHV underground cabling in the Netherlands

The worldwide demand for electricity, which is steadily increasing, leads to a continuous need for developing and extending the transmission networks. However, the installation of new overhead lines faces many challenges due to social, environmental and technical reasons. One solution that gains widespread public support is the installation of extra high voltage AC XLPE underground cable systems. Although this development is quite encouraging from a social perspective, new problems and challenges might arise, both from a technical and economical perspective. One significant area of concern is the reliability of underground cable systems. The current experience with EHV cables shows that although the cable failure frequency is very close to that of the overhead line, the additional components of the underground cable system (joints and terminations) reduce the reliability of the whole system. In addition, compared to overhead lines the EHV cables appear to have significantly longer repair times. The main goal of this thesis is to develop a reliability assessment approach in order to examine how the installation of EHV underground cables in transmission networks impacts the overall reliability level. First, an extensive literature review on basic reliability concepts and on main differences between OHL and UGC is conducted. In order to enrich the insight gained from this literature review, unstructured interviews took place with experts from the Dutch transmission system operator. By using the findings from both sources, a qualitative generic approach is proposed. This approach can be used as a framework for the decision making process that a planner should follow when he/she examines the possibility of installing EHV UGC in a transmission network from a reliability point of view. Different steps are included, from what input data are necessary until how to process and evaluate the results (reliability indicators) from the reliability assessment. The approach is used for the case study of the EHV Dutch transmission grid. A contingency analysis regarding failures of 380kV transmission overhead lines and underground cables is performed by using two methods: State Enumeration and Monte Carlo simulation. If a contingency leads to overloaded connections, remedial actions (such as generator re-dispatch within the Netherlands, cross-border re-dispatch and load shedding) are applied in order to relieve the overload. Then, several reliability indicators are calculated and the reliability level of the network is determined. A sensitivity analysis in the repair time and the failure frequency of EHV cables is conducted and the simulations are performed for different cable lengths and varying number of cable sections as well.

Subject

EHV cables
reliability
remedial actions
key performance indicators
repair time
contingency

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http://resolver.tudelft.nl/uuid:296239b2-a85e-4124-894e-009a7d3252c5

Embargo date

2015-09-30

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Student theses

Document type

master thesis

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Thesis_Nikoleta_Kandalepa.pdf

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