Important Reliability Indices Research Articles

Reliability Comparison of Rural & Urban LVDS Networks with Corresponding HVDS Networks Including Substation Reliability

This paper mainly determines the comparison of reliability of an existing rural area & urban area LVDS (low voltage distribution system) with their respective proposed high voltage distribution system (HVDS) and also including their 33/11 kV Substation. Ring main substation and single bus bar substation configuration are considered for urban and rural distribution systems respectively. The reliability of ring bus substation used in urban area is more as compared to single bus substation used in rural area. The load point reliability indices are calculated considering both substation reliability indices and radial feeder indices. The substation failure rate is calculated by considering overlapping outages approach and whereas the radial feeder indices are calculated by using cut set approach. Further, the LVDS Network is converted into the HVDS Network by replacing a high rating distribution transformer (DTR) supplying to a group of customers with Large in number with multiple small rating distribution transformers near to consumer terminals with less number of customers in each group. This conversion leads to Minimum length of LT Lines in HVDS Which results in improving voltage profile, reliability and efficiency. In this paper the disconnecting switches and alternative supply are also considered on both LVDS and HVDS Networks in the calculation of the reliability of to assess the reliability of the radial distribution system (FMEA)Failure mode effect analysis is used. This study uses a LVDS and HVDS system, and uses an alternative power source and disconnectors, to determine reliability indices of the rural area network and urban area network distribution system. In this paper the important distribution reliability indices to reduce system average interruption durations (SAIDI), Energy Not Supplied (ENS) and ASAI for LVDS and corresponding HVDS are calculated. The research idea is proposed on a Indian practical networks.

Reliability analysis for systems subject to mutually dependent degradation and shock processes

This paper studies the reliability problem for systems subject to two types of dependent competing failure processes, that is, soft failure and hard failure processes. A soft failure happens when the total degradation of the system exceeds a given critical level, while a hard failure occurs when the accumulative shock load caused by shocks surpasses the hard failure threshold. These two failure processes are mutually dependent due to the fact that external shocks will bring sudden increments in the degradation of the system, and the total amount of degradation will decrease the hard failure threshold of the system. The system fails whenever either of these two failure modes happens. Assuming that the arrival of shocks follows a Poisson process, the reliability function of the system under cumulative shock model is derived by using some analytical techniques. Some important reliability indices, including the mean lifetime of the system, the expected number of shocks until system failure, the probabilities of soft and hard failures, are calculated explicitly. Moreover, a special case that the hard failure process and soft failure process are mutually independent is also discussed. Monte Carlo method is employed to calculate the multiple integrals existing in the expressions of reliability function and reliability indices. A numerical example of the Reinforced Concrete pier columns on sea bridge is presented to illustrate the proposed model.

Reliability analysis of a complex repairable system in series configuration with switch and catastrophic failure using copula repair

This paper describes an analytical framework for in-depth investigation of a complex system consisting of two subsystems (namely L and M) in series configuration. Subsystem-L is composed of three identical units in parallel configuration that are working under 1-out-of-3: G policy, while subsystem-M has two non-identical units that are working under 1-out-of-2: G: policy. In subsystem-M, priority in operation is given to M1 unit whereas M2 unit put into cold standby mode if not in use. Moreover, both the subsystems are connected with controllers that may be perfect or imperfect at the time of need. We have considered a catastrophic failure due to frequent change in environmental conditions or man-made disruption. Failure rates of units in both the subsystems are constant and assumed to follow exponential distribution, but their repair supports two types of distributions namely general distribution and Gumbel-Hougaard family copula distribution. The system is studied by using the supplementary variable technique, Laplace transformation and Gumbel-Hougaard family of copula to derive differential equations and obtain important reliability indexes such as availability of the system, reliability of the system and profit analysis. The results have shown by tables and graphs. Conclusive part have been discussed in the last section of this study.

Reliability evaluation of permanent magnet synchronous generator‐based wind turbines considering wind speed variations

AbstractIn recent years, renewable resources, especially large‐scale wind farms, are increasingly used to generate clean electricity in modern power systems. The penetration level of these power plants is significant, and due to the variation in the wind speed resulting in the variation in the generated power, different aspects of power systems, especially reliability, may be affected that must be studied. Reliability evaluation of power system considering large‐scale wind farms is dependent on two factors: the failure rates of composed components including turbine, generator, electrical converters, transformer, and cable and the variation in the generated power arising from variation in the wind speed. In this paper, dependency of different component failure rates on the wind speed variation is considered, and using the Monte Carlo simulation, reliability evaluation of power systems containing large‐scale wind farms is performed. A wind farm equipped with the permanent magnet synchronous generator is considered, and the failure rate of composed components considering wind speed variation is determined. Based on the wind speed‐dependent failure rate associated with the components of energy conversion system, the important reliability indices of Roy Billinton test system including loss of load expectation and expected energy not supplied are calculated.

Reliability analysis of a complex repairable system in series configuration with switch and catastrophic failure using copula repair

This paper describes an analytical framework for in-depth investigation of a complex system consisting of two subsystems (namely L and M) in series configuration. Subsystem-L is composed of three identical units in parallel configuration that are working under 1-out-of-3: G policy, while subsystem-M has two non-identical units that are working under 1-out-of-2: G: policy. In subsystem-M, priority in operation is given to M1 unit whereas M2 unit put into cold standby mode if not in use. Moreover, both the subsystems are connected with controllers that may be perfect or imperfect at the time of need. We have considered a catastrophic failure due to frequent change in environmental conditions or man-made disruption. Failure rates of units in both the subsystems are constant and assumed to follow exponential distribution, but their repair supports two types of distributions namely general distribution and Gumbel-Hougaard family copula distribution. The system is studied by using the supplementary variable technique, Laplace transformation and Gumbel-Hougaard family of copula to derive differential equations and obtain important reliability indexes such as availability of the system, reliability of the system and profit analysis. The results have shown by tables and graphs. Conclusive part have been discussed in the last section of this study.

An efficient non-probabilistic importance analysis method based on MDRM and Taylor series expansion

The input variable of engineering structure inevitable has certain uncertainty. How to quantify the influence of those uncertainties on the uncertainty of structural response is an important issue in structural design. Non-probabilistic reliability importance analysis is one of the methods to quantify this influence when variable data information is insufficient. Although the method has great advantages for variables with insufficient data information, there is no efficient calculation method at present, and the excessive computational cost seriously hinders its application in actual engineering structures. In this paper, the multiplicative dimensional reduction method, Taylor series expansion and unary quadratic function are combined to put forward an efficient algorithm to estimate two non-probabilistic reliability importance indices. With the proposed method, all the calculation processes used to solve the extreme value of function are replaced by an approximate analytical solution. Since the proposed method is an approximate analytical solution, the calculation efficiency is extremely high. Three examples are investigated to verify the accuracy and efficiency of the proposed method.

Analysis of a Retrial Queue With Two-Type Breakdowns and Delayed Repairs

This article studies an M/G/1 retrial queue with two types of breakdowns. When the server is idle, it is subject to breakdowns according to a Poisson process with rate δ and it cannot be repaired immediately. While when the server is busy, it may break down according to a Poisson process with rate θ and can be immediately repaired. Firstly, based on embedded Markov chain technique and probability generating function (PGF) method, we present the necessary and sufficient condition for the system to be stable and the PGF of the orbit size at the departure epochs. Secondly, we give the steady-state joint queue length distribution by supplementary variable method, and present some important performance measures and reliability indices. Thirdly, we provide the analysis of sojourn time of an arbitrary customer in the system when the system is in stable state. Finally, some numerical examples are presented to illustrate the effect of the some system parameters on important performance measures and reliability indices.

An Unreliable Batch Arrival Retrial Queueing System With Bernoulli Vacation Schedule and Linear Repeated Attempts

This article deals with the steady-state behavior of an MX/G/1 retrial queue with the Bernoulli vacation schedule and unreliable server, under linear retrial policy. Breakdowns can occur randomly at any instant while the server is providing service to the customers. Further, the concept of Bernoulli admission mechanism is introduced. This model generalizes both the classical MX/G/1 retrial queue with unreliable server as well as the MX/G/1 retrial queue with the Bernoulli vacation model. The authors carry out an extensive analysis of this model. Namely, the embedded Markov chain, the stationary distribution of the number of units in the orbit, and the state of the server are studied. Some important performance measures and reliability indices of this model are obtained. Finally, numerical illustrations are provided and sensitivity analyses on some of the system parameters are conducted.

Analysis of an unreliable repeated service queue with delayed repair under randomized vacation policy

In this article we consider an unreliable MX/G/1 queue with two types of general heterogeneous service and optional repeated service subject to server’s break down and delayed repair under randomized vacation policy. We assume that customer arrive to the system according to a compound Poisson process. The server provides two types of general heterogeneous service and a customer can choose either type of service before its service start. After the completion of either type of service, the customer has the further option to repeat the same type of service once again. While the server is working with any types of service or repeated service, it may breakdown at any instant. Further the concept of randomized vacation is also introduced. For this model, we first derive the joint distribution of state of the server and queue size by considering both elapsed and remaining time, which is one of the objective of this article. Next, we derive Laplace Stieltjes transform of busy period distribution. Finally, we obtain some important performance measure and reliability indices of this model.

A Pragmatic Approach for Selecting a Suitable Wind Turbine for a Wind Farm Considering Different Metrics

This paper presents a new approach to select a suitable wind turbine (WT) for a wind farm (WF) site. In this approach, economy, reliability, resilience, and environmental aspects have been taken into account, as all the four aspects have a great deal of impact on the selection of a WT for a given site. Six commercially available WTs have been considered for this study. The energy output from a WF is significantly affected by wake, hence, in the proposed approach, placement of WTs in a WF is optimized using particle swarm optimization to reduce wake effect while increasing the energy production. A new algorithm has been proposed to find the reliability indices of the WF considering forced outage of WTs. In this context, two important reliability indices, such as expected energy not supplied and availability have been adopted to study the reliable viability of the optimized WF with all the six types of WTs. Power system resilience study has been gaining great deal of importance in recent times, but individual WF resilience study has not been addressed till now. This paper incorporates resilience as one of the criteria to select a suitable WT for any site. A new approach has been described in this regard to quantify the WF operational resilience by proposing an ideal resilience pentagon. The impact of all the six WTs on environment in terms of reduction of greenhouse gas emission has also been considered. Two different shaped WFs (same area) with same wind profile have been considered to study the proposed approach. A priority table has been formulated according to the ranking of WTs for different indices. The results show that the choice of WTs for WFs of different geometrical shape, however, with the same wind profile and the area may be different and largely depend on the choice of decision maker.

Reliability assessment of a gas generating station in Ogun State, Nigeria

This study evaluates and presents the reliability and availability of a power plant, Akute Power Plant, Ogun State, Nigeria, during the period of January – December, 2015. Time series load data on each generating unit were collected from Akute Power Plant daily operational log book from January to December 2015. Outages were classified into types, frequency and durations. The operational data for the above period was collected and analyzed using Reliability methods. Reliability conditions are defined with the collected data and types of the failure faced by each generating units. The most important reliability indices like mean time to repair (MTTR), mean time to failure (MTTF), mean time between failures (MTBF), repair rate (μ), failure rate (λ) were determined based on the loss of load approach. The reliabilities of each generating unit were evaluated on monthly basis for one year and the average availability of G1, G2, G3, and G4 were 0.9701, 0.9726, 0.9767, and 0.9707 respectively, while the reliability indices for G1, G2, G3, and G4 were 0.9860, 0.9880, 0.9854, and 0.9840 respectively. Suggestions were made to minimize system unavailability in order to improve the reliabilities of the network. Keywords: Reliability Methods, Mean Time To Repair, Mean Time Between Failure, Failure Rate

Reliability analysis of a phaser measurement unit using a generalized fuzzy lambda-tau(GFLT) technique

Nowadays power consumption is increasing day-by-day. To fulfill failure free power requirement, planning and implementation of an effective and reliable power management system is essential. Phasor measurement unit(PMU) is one of the key device in wide area measurement and control systems. The reliable performance of PMU assures failure free power supply for any power system. So, the purpose of the present study is to analyse the reliability of a PMU used for controllability and observability of power systems utilizing available uncertain data. In this paper, a generalized fuzzy lambda-tau (GFLT) technique has been proposed for this purpose. In GFLT, system components' uncertain failure and repair rates are fuzzified using fuzzy numbers having different shapes such as triangular, normal, cauchy, sharp gamma and trapezoidal. To select a suitable fuzzy number for quantifying data uncertainty, system experts' opinion have been considered. The GFLT technique applies fault tree, lambda-tau method, fuzzified data using different membership functions, alpha-cut based fuzzy arithmetic operations to compute some important reliability indices. Furthermore, in this study ranking of critical components of the system using RAM-Index and sensitivity analysis have also been performed. The developed technique may be helpful to improve system performance significantly and can be applied to analyse fuzzy reliability of other engineering systems.

An M/G/1 queue with two types of general heterogeneous service and optional repeated service subject to server’s breakdown and delayed repair

ABSTRACTIn this paper, we study the steady state behaviour of an M/G/1 queue with two types of general heterogeneous service and optional repeated service subject to server’s breakdowns occurring randomly at any instant while serving the customers and delayed repair. We assume that customers arrive to the system according to a Poisson process with rate ‘λ’ and the server provides two types of general heterogeneous service. At the beginning of a service, a customer has the option to choose any one type of service. After completion of either type of service, the customer has the further option to repeat the same type of service. For this model, we first derive the joint distribution of state of the server and queue size by considering both elapsed and remaining time, which is one of the objectives of this paper. Secondly, we derive the probability generating function of the stationary queue size distribution at departure epoch. Next, we derive Laplace–Stieltjes transform of busy period distribution and waiting time distribution. Finally, we obtain some important performance measure and reliability indices of this model.

Signature Based Reliability Analysis of Repairable Weighted k-Out-of-n:G Systems

In this paper, an exact formulation for computing reliability of weighted k-out-of-n:G systems using system signature is presented. Some component importance measures are computed. Moreover, reliability and some important reliability indices of repairable weighted k-out-of-n:G system are derived via system signature. A real life case of weighted k-out-of-n:G is analyzed using the proposed formulations to show the practicability of the given model.

Reliability evaluation of a Semi-Markov repairable system under alternative environments

ABSTRACTTo accurately describe the performance of repairable systems operating under alternative environments, for example, mild/harsh, working/idling, maximum/minimum level demand etc., a Semi-Markov process with a finite state space and two different Semi-Markov kernels is introduced. The state set of the system which is regarded as acceptable might depend on the environments. Two important reliability indices, the availability and time to the first system failure, are obtained via Markov renewal theory, transform and matrix methods. The results and numerical examples are also provided for two special cases: (1) when sojourn times under alternative environments are constants and (2) when sojourn times under environments have exponential distributions.

Reliability Modeling of a Solar Photovoltaic System using Supplementary Variable Technique

present study, an attempt has been made to derive the reliability measures of a solar photovoltaic system consisting of four subsystems arranged in a series. There is a single server who visits the system immediately to do repair of the unit. Failure time distributions are negative exponential while the repair time distributions of the subsystems are arbitrary. After repair, subsystems are ''as good as new''. Moreover, the whole system fails immediately when any subsystem fail. Switch devices are perfect. All random variables are statistically independent. Under these assumptions, using Markov process theory and the Laplace transform, some important reliability indexes and some steady state system indexes are derived. Finally, graphs for various measures of system effectiveness are derived using MATLAB to highlight the importance of the study.

Fuzzy reliability analysis of dual-fuel steam turbine propulsion system in LNG carriers considering data uncertainty

This paper presents an approach to analyze the fuzzy reliability of dual-fuel steam turbine mechanical propulsion conventional (DFSMC) system of LNG carriers utilizing best available data collected from various sources which may have some sort of uncertainties. Quantification of uncertainties present in collected data has been done through data fuzzification using triangular fuzzy numbers with known spreads as suggested by system experts. In these conditions, if available techniques such as FLT (fuzzy lambda-tau) and GABLT (genetic algorithms based lambda-tau) are applied for DFSMC system reliability assessment using quantified data then the computed reliability indices have wide ranges of prediction due to the complexity of the system. Using these results, decision-maker may suggest some impressive corrections which may improve the system performance. However, it may also be possible that after incorporating suggested corrections, system performance may not improve upto the desired level because suggestions are inappropriate due to the wide ranges of prediction. In order to reduce the prediction ranges of computed fuzzy reliability indices, and to select suitable and effective strategic decision making, this study applies the weakest t-norm (Tω) based approximate arithmetic operations for evaluating some very important fuzzy reliability indices of the system. Sensitivity analysis has also been conducted in an ideal condition for analysing the effects of various reliability parameters on system performance. To rank the critical components of the system, Tanaka et al. (1983) approach has been extended for repairable systems and then utilized for this purpose. The analysis can help maintenance personnel to understand and plan suitable maintenance strategy to improve the overall performance of the system. Based on results some influential suggestions are given for improving system performance.

Fuzzy reliability analysis of repairable industrial systems using soft-computing based hybridized techniques

The purpose of the present study is to analyze the fuzzy reliability of a repairable industrial system utilizing historical vague, imprecise and uncertain data which reflects its components’ failure and repair pattern. Soft-computing based two different hybridized techniques named as Genetic Algorithms Based Lambda–Tau (GABLT) and Neural Network and Genetic Algorithms Based Lambda–Tau (NGABLT) along with a traditional Fuzzy Lambda–Tau (FLT) technique are used to evaluate some important reliability indices of the system in the form of fuzzy membership functions. As a case study, all the three techniques are applied to analyse the fuzzy reliability of the washing system in a paper mill and results are compared. Sensitivity analysis has also been performed to analyze the effect of variation of different reliability parameters on system performance. The analysis can help maintenance personnel to understand and plan suitable maintenance strategy to improve the overall performance of the system. Based on results some important suggestions are given for future course of action in maintenance planning.

Importance analysis for reconfigurable systems

Importance measures are used in reliability engineering to rank the system components according to their contributions to proper functioning of the entire system and to find the most effective ways of reliability enhancement. Traditionally, the importance measures do not consider the possible change of system structure with the improvement of specific component reliability. However, if a component׳s reliability changes, the optimal system structure/configuration may also change and the importance of the corresponding component will depend on the chosen structure. When the most promising component reliability improvement is determined, the component importance should be taken into account with respect to the possible structure changes. This paper studies the component reliability importance indices with respect to the changes of the optimal component sequencing. This importance measure indicates the critical components in providing the system reliability enhancement by both enhancing the component׳s reliability and reconfiguring the system. Examples of linear consecutive-k-out-of-n: F and G systems are considered to demonstrate the change of the component Birnbaum importance with the optimal system reconfiguration. The results show that the change of the importance index corresponds to the change of the system optimal configuration and the importance index can change not monotonically with the variation of the component reliability.

An unreliable retrial queue with delaying repair and general retrial times under Bernoulli vacation schedule

This paper deals with the steady state behavior of an M/G/1 queue with general retrial time and Bernoulli vacation schedule for an unreliable server, which consist of a breakdown period and delay period. While the server is working with primary customers, it may breakdown at any instant and server will be down for short interval of time. Further concept of the delay time is also introduced. The primary customer finding the server busy, down or vacation enters a group of unsatisfied customer called orbit. After the completion of a service, the server either goes for a vacation of random length with probability p or may continue serve for the next unit, if any with probability (1−p). For this model, we first derive the system size distribution at a departure epoch. Secondly, we derive the probability generating function of joint distributions of state of the server and queue size, which is one of chief objectives of the paper. Finally, we obtain some important performance measures and reliability indices of this model.