Accounting for component condition and preventive retirement in power system reliability analyses

Abstract

Deteriorated power system components have a higher probability of failure than new components. Still, the reliability of supply analyses traditionally models all components of the same type with the same probability of failure, and thus neglects the effect of deteriorated components. This paper presents a methodology to integrate a condition-dependent component probability of failure model into a power system reliability analysis. The component state is described by a semi-Markov process, and the paper shows how this, under reasonable assumptions, can be approximated by a Markov process. The Markov assumption simplifies the analysis and allows the model to include preventive retirement and be calibrated to statistical data. A case study using statistical data for Norwegian power transformers shows that, in the Norwegian power system, the proportion of failures that are due to the poor condition is small, partly due to the common strategy of preventive retirement. However, if the condition of the transformers were worse, the impact of poor conditions can be considerable. The methodology further enables the identification of the transformers that contribute most to the risk to the reliability of supply. The paper thus highlights the importance of accounting for the component condition in strategic decisions such as long-term renewal planning 1This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Estimating Uncertainty in Reliability of Electricity Supply Analyses Considering Component Condition

“…This section gives a brief recap of the component reliability model introduced in (Toftaker, Foros, and Sperstad 2023) and (Toftaker and Sperstad 2022). The main purpose of the reliability model is to include technical condition of individual power system components in the system reliability analysis.…”

“…The time until preventive replacement is for simplicity assumed to be exponentially distributed with rate . Following (Toftaker, Foros, and Sperstad 2023) ) + where it is assumed that the present time is = 0. If a wear-out failure occurs, the transformer is replaced and its apparent age restarts at 0.…”

“…For any failure the time spent in a failed state is exponentially distributed with rate . Following (Toftaker, Foros, and Sperstad 2023) we assume that that within a one-year analysis horizon the technical condition does not change significantly and that after the component is replaced, the probability of wear out failure is negligible. This means the functional state of the component is well described by a Markov model where the time to wear-out failure is exponentially distributed with rate…”

“…Integration of component condition in system reliability has been the topic of several research articles, e.g., (Li 2002) which handled end of life failures for transformers or (J. H. Jürgensen, L. Nordström, and P. Hilber 2019) which handled condition dependent repairable failures. Recent work (Toftaker, Foros, and Sperstad 2023) has shown how one may account for both condition dependent failures and preventive replacement for transformers in PSRA and how this can be carried out over an extended time horizon of several years (Toftaker and Sperstad 2022).…”

“…This paper builds on the work in (Toftaker, Foros, and Sperstad 2023) and (Toftaker and Sperstad 2022), which presented estimates for condition-dependent reliability indices but no estimate for their accuracy. A novel method to estimate the uncertainty in reliability indices is thus presented.…”