# Life Cycle Cost Estimation and Analysis of Transformers Based on Failure Rate
## 1 Introduction
On the basis of ensuring power supply safety and reliability, investment costs should be minimized to the greatest extent possible [11]. Due to the complex structure and multiple types of faults in power transformers, scholars at home and abroad have classified the faults of power transformers into different types based on their properties. (1) According to the main structure of transformers, power transformer faults are divided into winding faults, iron core faults, insulation oil faults, and accessory faults. (2) According to the division of transformer fault-prone areas, transformer faults are divided into insulation faults, iron core faults, and tap changer faults. (3) From the circuit division of transformers, transformer faults can be divided into circuit faults, magnetic circuit faults, and oil circuit faults. In the study of fault statistics based on a large number of transformers, a three-layer fault tree model corresponding to transformers was established with transformer structure as the main auxiliary and transformer prone fault areas. Transformer faults are divided into seven categories: lead fault, winding fault, iron core fault, bushing fault, oil conservator fault, tap switch fault, and other faults. For each fault category, causal logical relationships are searched and corresponding bottom events assigned from a large number of fault events, and the occurrence of bottom events leads to the occurrence of intermediate events. Subsequently, the probability importance analysis in fault tree analysis is used to assign corresponding weights to each bottom event, and then the transformer failure rate is obtained through probability statistics of the event and the corresponding top event calculation formula. The corresponding distribution of transformer failure rate is drawn through the estimation model of transformer failure rate, the maintenance interval of the transformer is determined based on the distribution map, and the corresponding full life cost of the transformer is further calculated. Finally, a more accurate estimate of the full life cycle cost is obtained, which assists in transformer selection and arrangement of transformer maintenance during substation construction. Life cycle cost (LCC) pertains to the comprehensive expenditure incurred by a system or equipment over its entire life cycle, encompassing the direct, indirect, and recurring costs associated with its design, research and development, manufacturing, utilization, maintenance, and support [12]. This encompasses all one-time and related expenses until the eventual decommissioning of the system or equipment. The culmination of all these one-time and interrelated costs provides a comprehensive understanding of the economic implications involved in the entire life cycle of the system or equipment, shaping decision-making processes and financial planning until its eventual retirement. LCC management has three major characteristics: full system, full cost, and full process. Among them, the whole system refers to the comprehensive consideration of costs in different stages such as planning, design, infrastructure, and operation, with the overall benefits as the starting point, in order to seek the best solution. Full cost is the consideration of all costs that may arise, seeking a balance between appropriate availability and full cost. The entire process is to consider the entire life cycle from planning and design to scrapping, and it is required to ensure the application of the LCC method from an institutional perspective. As far back as 1904, Sweden [13] laid the groundwork for the comprehensive consideration of life cycle costs in railway construction. It was not until 1947, however, that the United States formally instituted the value analysis method, marking the inaugural application of the LCC concept in both technical and economic analyses [14]. Despite these early initiatives, it took until the latter half of the 20 th century for the global community to recognize and earnestly delve into the significance of LCC.