# Life Cycle Cost Estimation and Analysis of Transformers Based on Failure Rate
## 5 Conclusions  
In this study, the application of life cycle cost theory was applied to the cost evaluation of power transformers and an in-depth study was conducted using the life cycle cost of 110 kV transformers as an example. Based on the distribution of transformer failure rates, the corresponding life cycle cost of transformers can be fitted to assist in the procurement and maintenance arrangements of transformers, and the following conclusions have been drawn:  
1. Based on a large number of fault statistics of transformers, this study established a three-layer fault tree model for transformers with transformer structure as the main auxiliary and combined with transformer prone fault areas. Transformer faults were divided into seven major categories: lead fault, winding fault, iron core fault, bushing fault, oil conservator fault, tap switch fault, and other faults. By analyzing the probability statistics of bottom events, intermediate events, and top events, the transformer failure rate can be obtained. 2. This study comprehensively analyzed the operating, maintenance, failure, and scrapping costs of transformers during their service life using historical operating data provided by a northern power company. Based on the calculated failure rate distribution, a dataset of the full life cost of various transformers was constructed and effective prediction of the life cost of transformers was provided as a reference indicator for power enterprises to bid and invest. 3. Equipment procurement management should not only focus on the initial procurement cost of equipment but also include various aspects of the entire life cycle. By estimating and analyzing the full life cycle cost of transformers with different voltage levels, it was found that, the higher the voltage level, the higher the initial procurement cost of transformers. However, the full life cycle cost of transformers with higher initial costs may not necessarily be higher than that of other transformers. 4. Due to the late start of transformer maintenance work, the available statistical data are not yet very detailed. In future research, we will further conduct in-depth research, collect more detailed transformer inspection data, and use more accurate fitting methods, combined with investment payback time and net present value, to better measure the multidimensional benefits of various equipment. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Item** & **Mean Value (USD k)** & **Fluctuation Range (USD k)** \\ \hline \multirow{2}{*}{MF1} & 35 kV transformers & 19.40 & 12.53–21.76 \\  & 110 kV transformers & 76.71 & 56.53–85.78 \\ \hline \multirow{2}{*}{MF2} & 35 kV transformers & 16.93 & 11.28–20.68 \\  & 110 kV transformers & 77.74 & 57.27–106.88 \\ \hline \multirow{2}{*}{MF3} & 110 kV transformers & 56.69 & 26.93–57.93 \\  & 220 kV transformers & 152.37 & 118.57–188.64 \\  & 750 kV transformers & 190.67 & 174.07–212.46 \\ \hline \multirow{2}{*}{MF4} & 110 kV transformers & 72.00 & 49.02–75.76 \\  & 220 kV transformers & 15.60 & 9.19–20.44 \\ \hline \multirow{2}{*}{MF5} & 35 kV transformers & 20.81 & 9.17–23.26 \\  & 110 kV transformers & 139.88 & 54.90–224.85 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of life cycle costs of transformers from different manufacturers. **Author Contributions:** Conceptualization, writing--original draft preparation, writing--review and editing, X.Z. ; Conceptualization, supervision, H.C. and P.P. ; methodology, F.G.; software, L.F. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the Science and Technology Project of State Grid Corporation of China, grant number 5200-202356133A-1-2N, \"Research on key technologies of scheme optimization and cost control for transmission and transformation projects considering the development of a unified large market and carbon emission reduction\". **Data Availability Statement:** Data is contained within the article.