Reliability Evaluation of Electric Power Systems Integrating Cable Design and Ageing

Abstract

The restructuring of the electricity sector forces utilities to operate their existing power networks with increasing flexibility and efficiency. Alternative cable rating methods, such as emergency and dynamic ratings, improve the utilisation of existing network cables, and provide cable-based networks with additional flexibility and resilience against uncertainties. However, such approaches may pose more stress on network cables and increase the risk of thermal overloading and ageing. This thesis advances the existing power system reliability assessment methodology by integrating a detailed cable system thermal-ageing model that considers cable design properties and environmental conditions into a traditional sequential Monte Carlo simulation. The main outcome of this integration was the comprehensive probabilistic evaluation of cable networks’ reliability, together with each individual cable’s thermal performance and ageing risk. The methodological framework integrating cable design and ageing provides operators with the additional tools to identify key network cables based on a quantified ageing index in order to perform optimised cable replacement and maintenance strategies. The framework has also helped utilities and operators to propose alternative cable operating practices to increase the loadability and flexibility of cable-based networks for better network performance, but also to avoid excessive risk of cable ageing. The methodological framework was applied on four test networks for four specific case studies. The first study presented an innovative methodology to capture the additional risk of cable failure and ageing when cables are operated beyond their limits. The second study further quantified the network reliability benefits and cable ageing risks when extended durations and increased ampacity of the emergency ratings are implemented. These two studies will inform the utilities of the benefits and risks of implementing emergency rating of UGCs and to help them to make decisions related to optimising their operational flexibility. The third study proposed an alternative flexible cable current rating method to optimise the loading capability of existing cable tie lines between wind farms and host utilities. It allows the wind farm developers to increase their generation capacities without upgrading their existing cable tie circuits and risking the cable lifetime. The last study evaluated the benefits and potential risks of emergency ratings of UGCs could give in a distribution cable network with EV connections. The proposed emergency rating approach enables for a higher penetration level of EVs while an acceptable level of cable ageing is generated.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Kostas Kopsidas (Supervisor) & Sinisa Durovic (Supervisor)