# Maintenance Management of a Transmission Substation with Optimization
## 1 Introduction
This procedure is possible only with the inclusion of optimization algorithms in the maintenance process. Devices that are less important in the system, however, affect maintenance processes with reduced intensity. The maintenance processes can be influenced by computation of the importance and technical condition of EPS elements, which is based on historical data of operation, events, and monitoring of EPS elements' technical condition. This represents the main hypothesis of this article. The inclusion of optimization processes in the analysis of maintenance procedures enables a reduction of maintenance costs, which represents the second hypothesis. The methodology of computation of frequency of EPS elements' maintenance influences the maintenance processes and is based on available historical operation data and statistics of events on EPS elements. For the entire EPS, we computed the availability of elements in connection with the transmissioned energy. The availability of elements and commissioned energy to final customers are reliability indicators. The values of these indicators for individual elements were then compared with the reliability indicators of similar elements operated by other system operators. The importance of elements were computed on the basis of these data. In connection with the technical conditions of elements that are performed in practice through monitoring, it is possible to influence the maintenance processes on the basis of the RCM maintenance concept. The optimization process that uses all possible data on historical events of operation and maintenance costs yields the results that can be used to manage the maintenance processes in the future. This represents the main originality of this paper. The existing method of assessing the technical condition of EPS elements was upgraded and included actively in the optimization process, where we predicted a dynamic changing of the technical condition of elements due to the interventions to the existing maintenance process. The significant states in the system are determined on the basis of EPS operation data that include generation, nodal loads, and load flows between the nodes. Their inclusion in the optimization process enables that maintenance activities are performed in the most suitable significant state. Thus, the maintenance activities have the least impact on the EPS operation. Indirectly, this also influences operational reliability and maintenance costs. The optimization process in our article affects the frequency of transitions between maintenance processes. The past data on the operation of transmission elements that are covered by statistics of events were the basis for calculation of reliability indicators of these elements and their unavailability. The values of these indicators for individual elements were compared with reliability indicators of similar elements operated by other system operators. The paper consists of six sections. Section 2 presents the RCM concept-based maintenance model. A switching bay was represented with an index of technical condition and an index of importance. The costs of the existing maintenance concept were analyzed in detail. Section 3 provides the basic data for the optimization model. The key data in the RCM maintenance process were the values of technical condition and reliability indicators for every EPS element. The data are also given on the expected costs of outages and maintenance costs for the example presented in this article. Section 4 presents the link between the maintenance model and the optimization algorithm. Three objective functions and one penalty function were defined to reach the optimal RCM maintenance concept. The results of the optimization process are given in Section 5. The optimal method and period of maintenance were defined accurately for each EPS element. A comparison was also given of maintenance costs with the existing time-based maintenance and with the new RCM maintenance concept. Section 6 provides the discussion and outlines the future work.