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Title: Probabilistic risk assessment of electrical substations
Author: Dimopoulos, Athanasios
ISNI:       0000 0004 2748 8835
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2009
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This thesis is concerned with the development of probabilistic risk assessment for substation earthing systems. A number of key parameters have been studied in detail which led to the development of a new approach that incorporates the recommendations of applicable standards and uses historical system fault data to take account of the probabilistic nature of load, protection systems and grid characteristics. In this work, an in-depth appraisal of existing standards has led to the development of safety-limit surfaces that can be used to quantify the benefits/disadvantages of particular earthing standards. The investigation has revealed that there are substantial differences between the recommended values of tolerable voltages attributed to a combination of factors: (i) difference in assumed tolerable body current (ii) differences in the parameters of the electrocution circuit (iii) differences in the predicted touch voltage and (iv) differences in the assumed worst-case shock location. The electricity industry, like other industries, is looking to reduce risk to minimum feasible while maintaining costs of mitigation within acceptable limits. Therefore, a more rigorous and comprehensive procedure of probabilistic risk assessment of the earthing systems is required. In order to achieve this, a detailed analysis of all parameters was undertaken in this work using more representative accidental circuits and parameters extracted from historical system fault data, provided by the collaborating transmission companies. These parameters were modelled and integrated into the proposed probabilistic risk assessment process. Work within this investigation on improving accuracy of calculation of heart fibrillation has led to the development of a probability surface of ventricular fibrillation and a computerised process that determines an accurate probability for a given body current and shock duration. This procedure takes into consideration the body current path and eliminates reading errors or assumptions that could result into conservative or optimistic conclusions. The above fundamental investigations on parameters affecting the overall risk were implemented in a new computerised risk assessment procedure CRAFTS suitable for transmission systems. CRAFTS allows a probabilistic risk assessment of the system under investigation. The application integrates the recent developments in the latest standard IEC 60479-1 and the developed probability surface of ventricular fibrillation. A case study performed on a typical grid has shown that the developed program is very useful when applying sensitivity analysis of the various parameters of the system and accidental circuit. The proposed full probabilistic risk assessment method incorporates the earthing system simulation results performed by specialised software, namely CDEGS, making it possible to simulate different electrocution scenarios throughout the substation instead of assuming a 'worst case scenario' and exposure to maximum possible voltages. Overall, the research in this thesis, offers an integrated solution of probabilistic risk assessment of earthing systems in aid of sound cost/benefit analysis and decision making.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available