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Overview of Power System Reliability
Published in Isa S. Qamber, Power Systems Control and Reliability, 2020
The MTTR expression is defined as the total maintenance time divided by the total number of maintenance actions over a specific period. In other words, it is a basic technical measure of the maintainability of equipment and repairable parts. Also, the term MTTF (Çekyay and Özekici, 2015) is defined as to run controlled tests for component to see how reliable a component is expected to be. Sometimes report the results coming out of the carried-out test. This is a good indication of the reliability of a component, as long as these tests are reasonably accurate. The MTTF is a basic measure of reliability for non-repairable components. The MTTF is calculated as the total time of operation divided by the total number of components. It has the following expression: MTTF=TotalHoursofOperationTotalNumberofComponents
Equipment Reliability
Published in Robert Doering, Yoshio Nishi, Handbook of Semiconductor Manufacturing Technology, 2017
Formally, maintainability is the probability that the equipment will be restored to a specific operational condition (able to perform its all intended functions) within a specified period of time, when the maintenance is performed by personnel having specified skill levels and using prescribed procedures, resources, and tools. Maintenance can be either unscheduled or scheduled. One of the most popular measures of maintainability is mean time to repair mean time to repair (MTTR), given by: Mean time to repair (MTTR)=Total repair timeNumber of repair events Repair time includes diagnosis, corrective actions, and verification tests, but not maintenance delays.
Reliability Analysis
Published in Armand A. Lakner, Ronald T. Anderson, Reliability Engineering for Nuclear and Other High Technology Systems, 2017
where MTBF = mean time between failure and MTTR = mean time to repair. This formula represents an average availability, which is based on the continuous duty cycle of a system having a constant failure rate and repair rate. As the formula indicates, when downtime is zero (i.e. when MTBF approaches infinity or when MTTR nears zero) then availability, A, is one. Thus, near zero downtime becomes an engineering objective and MTBF and MTTR are the parameters which directly affect the percentage of time that a system is available for use. While any discussions of R&M theory may tend to treat reliability and maintainability as separate topics for reasons of clarity, the combined effect of both must ultimately be considered in the planning stages of any system. A number of combinations may be possible for achieving the same desired level of system availability. The specific tradeoff which is selected will also be influenced by environment, cost, personnel training or other external constraints which are also important to the utilization of the equipment.
Buffer allocation design for unreliable production lines using genetic algorithm and finite perturbation analysis
Published in International Journal of Production Research, 2022
Khelil Kassoul, Naoufel Cheikhrouhou, Nicolas Zufferey
This example was initially proposed by Ho, Eyler, and Chien (1979) and used in different papers as a benchmarking case (Gershwin and Schor 2000; Massim et al. 2012; Demir, Tunali, and Eliiyi 2011; Kose and Kilincci 2015). The total buffer size is 31, and the parameters of the five machines are presented in Table 4. For this example, the average production rate is estimated by simulating 100,000 parts with 50 replications. MTTR and MTBF denote the mean time to repair and the mean time between failures, respectively. Table 4 presents the buffer sizes configuration and the corresponding average production rates obtained by the different approaches. GA-FPA obtains a slightly better production rate with the buffer size configuration (7, 11, 9, 4), which has the same allocation at the extremities of the line as Kose and Kilincci (2015), Demir, Tunali, and Eliiyi (2011), Massim et al. (2012) and Gershwin and Schor (2000). The allocation of small capacities at the beginning and at the end of the line, and important sizes in the middle, is likely to be efficient for facilitating the passage of the parts and thus bypassing a possible congestion of the line. Again, we can see that GA-FPA obtains the best results.
RAMI Analysis for PF Power Supply System of ITER
Published in Fusion Science and Technology, 2022
Li Jiang, Ge Gao, Zhengyi Huang, Jie Zhang, Peng Wu, Xuesong Xu
The last step of the RAMI analysis is the RBD analysis, which uses blocks to represent the function of the system as defined in the FA stage and calculates the reliability and simulates the availability of the system by using BlockSim software. The input data of the RBD analysis are failure rate λ, mean time to repair (MTTR), duty cycle, and so on. The λ means the inherent frequency with which a system or component fails. The MTTR represents the average time required to repair a failed component. The duty cycle is the ratio of the operating time of the component compared to the total operating time of the system. All these input data are derived from the manufacture reliability data sheet, industry standards, and previous experience compiled in other scientific facilities. Several initial and expected input datas for simulation of RBD are shown in Table IV.
Measuring sequence stability in automotive production lines
Published in International Journal of Production Research, 2021
Mareike Müller, Marcel Lehmann, Heinrich Kuhn
Time-oriented measures evaluate the production process on meeting the target schedule. The overall lead time of an order, as a prominent example, is the period from the beginning of the production process in the body shop to delivery to the distribution centre. This includes processing-, queuing- and transportation-time. One very important measure in automotive production is the lead time required to complete a single task. It is called takt time, and the configuration of assembly shops is usually based on this figure. Another group of indicators are non-productive time related, and measure when production machines or units fail to perform. They consist of idle time, set-up time and the mean time to repair (MTTR). The MTTR represents the average time required to fix a failed component or machine. Reducing the MTTR decreases the downtime as well as the lead time. Tracking and reducing the lead time, WIP, takt time, downtime and MTTR helps to identify bottlenecks in the production process and is considered one of the most essential goals of continuous improvement (Li 2013).