Theoretical and practical aids for the proper selection of reliability models for power system components

In the deregulated electrical energy market, reliability estimation of electrical components is an increasingly important, but difficult, task. Indeed, utilities face on one hand the degradation of many power system devices and on the other hand the high‐reliability of such devices. This paper gives theoretical and practical aids for the proper selection of reliability models for power system components. Firstly, the most adopted reliability models in the literature about electrical components are reviewed and the classical ‘direct reliability assessment’ is described. Then, phenomenological and physical models for the estimation of ageing and life of electrical insulation (the weakest part of many devices) are illustrated. Finally, numerical and graphical examples show that seemingly similar reliability models can possess very different lifetime percentiles and hazard rates. Thus model selection must be accomplished very carefully, since it involves completely different maintenance actions and costs.