In this paper, we apply the Failure Modes, Effects, and Criticality Analysis (FMECA) approach to the criticality and risk analysis of the efficiency, safety/reliability, environment, and financial criteria of the high voltage transmission line. In the efficiency analysis, the weighting-scoring method and analytical hierarchy process are applied to obtain the line renovation index, which is interpreted as efficiency severity. The safety/reliability severity relates to the system impacts are caused by failure of the equipment and the system. The environmental severity takes social impacts and pollution into consideration. The financial severity involves the cost of spare parts and maintenance costs, which are interpreted as the financial severity of the lines. Twenty practical transmission lines in Thailand with actual data for 115, 230, and 500 kV were studied. The transmission line components are divided into eight components including the conductor, conductor accessories, insulator, steel structure, foundation, lightning protection system, tower accessories, and right-of-way. The severity and criticality of the components and transmission lines are analyzed and plotted in criticality matrices based on four criteria. This criticality matrix is presented at four different levels including very low, low, medium, and high risk, as represented by four color bands: green, yellow, orange, and red, respectively. The results show that three 115 kV lines are the first priority for short-term reconstruction planning because of their unacceptable condition and high risk in terms of safety/reliability and financing. Recommendations for maintenance strategy and risk mitigation are proposed for the utility according to the utility’s actual criticality. Ultimately, maintenance planning of the transmission system can be effectively managed with higher reliability, a lower risk of failure, and a lower cost of maintenance.

This paper develops a comprehensive framework for the risk assessment of 115 kV power circuit breakers (PCBs) by evaluating their condition, replacement needs, and criticality to the electrical network. The primary objective is to create a risk assessment tool that enhances maintenance practices and improves operational efficiency. The framework begins with a condition assessment, quantified through the use of a health index, derived from historical diagnostic test results and routine checks. The next step involves a replacement assessment, using a replacement index that considers factors such as age, rating adequacy, and technological obsolescence to determine the necessity of replacement. Finally, a criticality assessment is performed using a criticality index, which evaluates the PCB’s role in the network by factoring in location, load importance, failure severity, and the consequences of failure on network operations. By integrating these indices, the framework offers a holistic view of the associated risks. The methodology is applied to assess the risk of 149 sample PCBs across 30 substations in Thailand, with relevant data collected for each unit. The resulting risk assessments support proactive maintenance, minimize downtime, optimize the allocation of limited resources, and enhance the overall efficiency, reliability, and safety of the electrical network.

In this paper, a new D-distance factor is proposed to determine the failure probability and to prioritize maintenance actions of power circuit breakers in high-voltage substations. The D-distance factor is calculated by using the condition index and renovation index of a high-voltage circuit breaker (HVCB). To facilitate effective decision-making on maintenance with a simple method and less computational effort, the proposed model incorporates the weighting–scoring method (WSM) and analytical hierarchy process (AHP) with the various diagnostic methods for condition index assessments as well as the operation requirements of HVCBs for renovation index assessments. Many significant parameters from circuit breaker testing, such as insulation resistance, contact resistance, contact timing, SF6 gas measurements, gas leakage rate, visual inspection, etc., have been considered for condition index determination. In addition to these, other significant parameters, such as age of the circuit breaker, age of the interrupter and mechanism, number of fault current interruptions, actual load current to rated current ratio, actual short circuit current to rated interrupting current ratio, maintenance ability, spare parts availability, maintenance expertise level, etc., are also considered for renovation index determination. To validate the proposed model, the practical test data of twenty 115 kV HVCBs in various substations of a distribution utility in Thailand were utilized and tested. By analyzing the actual condition and operation requirement of the circuit breaker, the output, as the condition index and renovation index using the proposed method, is discussed with HVCB experts in the utility to adjust the scores and weights of all criteria to obtain the most accurate and reliable model. The results show that the D-distance technique measured from the risk matrix, which is defined as the failure probability, can be used to rank the maintenance schedule from urgent to normal maintenance tasks. In addition, various failure probabilities in the risk matrix of the circuit breaker can be used to determine the appropriate maintenance strategies for the power circuit breaker in each group. Finally, the proposed method could help the utility managers and maintenance engineers manage the maintenance planning effectively and easily for thousands of HVCBs in the grid, and it can be further applied with other high-voltage equipment in both transmission and distribution systems to facilitate the maintenance activities according to available costs and human resources.

Asset Management of Power Transformer Protective Devices in Transmission System