Data-driven system reliability and failure behavior modelling using FMECA

System reliability modelling needs a large amount of data to estimate the parameters. In addition, reliability estimation is associated with uncertainty. This paper aims to propose a new method to evaluate the failure behavior and reliability of a large system using failure modes, effects and criticality analysis (FMECA). Therefore, qualitative data based on the judgment of experts is used when data is not sufficient. The subjective data of failure modes and causes has been aggregated through the system to develop an overall failure index (OFI). This index not only represents the system reliability behavior but also prioritizes corrective actions based on improvements in system failure. In addition, two optimization models are presented to select optimal actions subject to budget constraint. The associated costs of each corrective action are considered in risk evaluation. Finally, a case study of a manufacturing line is introduced to verify the applicability of the proposed method in industrial environments. The proposed method is compared with conventional FMECA approach. It is shown that the proposed method has a better performance in risk assessment. A sensitivity analysis is provided on the budget amount and the results are discussed.Hadi A. Khorshidi, Indra Gunawan, and M. Yousef Ibrahi

Multi-state reliability analysis of rotor system using Semi-Markov model and UGF

In order to accurately reflect the performance degradation law of the aero-engine rotor system during its life span, a novel multi-state reliability analysis method for rotor system is proposed. The method is based on the combination of the Semi-Markov model with UGF technique. The Semi-Markov model is used to describe the performance degradation process of the components of the rotor system. The UGF technique is utilized to exhibit the relationship between the state performance and the performance probability of the components. Furthermore, the UGF of the entire rotor system is obtained by simplifying the system structure with the modularized method. Therefore, the reliability of the rotor system at different task performance levels can be evaluated easily. A practical case study based on a turboprop engine rotor system is performed to illustrate the implementation and efficiency of the proposed reliability analysis method. Meanwhile, compared with the conventional method, the analysis results indicate that the proposed method can reflect the performance degradation process of the rotor system more veritably and effectively

AVAILABILITY MODEL FOR A COG EN ERA TION SYSTEM SUBJECTED TO REDUNDANCY

The main emphasis of cogeneration system is to provide electrical energy, steam, hot and chilled water to their customers. The failure of this system could lead to the disruption of the supply of these items. If failure occurs, it will result in reduction of availability as well as economic loss. In order to mitigate such effects, it is required to study availability of the cogeneration system together with associated economic loss. However, there are factors which affect the availability assessment of the cogeneration system. These factors are system redundancy and limitation of maintenance data. Use of redundancy in cogeneration helps to achieve higher availability but the operation cost of redundancy is expensive due to maximum demand charge cost. Thus, it is important to consider the economic effect of redundancy

DC collection systems for offshore wind farms

Power generation through natural resources has found to be one of the best options to minimise climate change and global warming concerns. Among the naturally replenish sources, power generation from offshore wind accounts for a larger share. This has been showcased by the rapid development of offshore wind farms (OWF)s especial in the North sea. At the OWF collection system level, only alternating current (ac) technology is being used at present. Conversely, the use of direct current (dc) technology could provide additional benefits in terms of control flexibility, minimising system losses, and increasing power density of components. However, there are still a number of technical challenges that require addressing. One of the major aspects is the reliability of this concept as a whole. The research work presented in this thesis is aimed to address the existing challenges, in particular, from the component level to the system level from the perspective of reliability. The main contributions of this research work comprise of four parts, namely, (1) reliability analysis of semiconductors of dc-wind turbine machine side converter, (2) propose a new selection guideline based on reliability and costs to identify the most suitable multi-level converter topology for offshore wind power dc collection systems at different voltage levels and power levels, (3) identification of the most suitable dc collection system topology in terms of reliability and other economic factors, and (4) development of an analytical methodology to asses the availability of offshore wind farms considering the cable network dependency. One of the key building blocks of a dc collection system is the dc wind turbine (dcWT). The lifespan of a wind power system is highly influenced by the reliable operation of its power converter. A mission-profile based reliability assessment technique considering long-term and short-term thermal cycles are used to evaluate the lifetime of power electronic components of a dual active bridge based dcWT. Further, to ensure an effective lifetime evaluation of the entire converter system, a Monte Carlo method is used to generate the lifetime distributions and entire unreliability functions for power semiconductors. To utilise the full capacity of the dc technology in the context of the OWF collection system, the selection of a suitable power electronic converter topology is a key aspect. iii iv A selection criterion based on the optimal redundancy level with the consideration of the converter reliability, preventive maintenance interval, operational efficiency, the total cost of ownership and return on investment is proposed. The primary motivation of this work is to investigate the feasibility of utilising suitable multi-level voltage source converter topologies at different medium voltage dc levels and power levels. To select a suitable dc collection system topology, a comprehensive analytical reliability evaluation method based on Universal Generating Function (UGF) is proposed with associated economic factors. This strategy combines the stochasticity of wind with multiple power output states of a single wind turbine (WT). Subsequently, the relationship between the output states and corresponding state probabilities of WTs are combined using the UGF technique considering the network structure. To identify the best topology, the investment- and operating- costs (which includes network losses) are incorporated. The OWF collection system is made up of a considerable number of inter-array cables. The effectiveness of the OWF to export energy to the grid depends on the availability of that network. Therefore, it is imperative to include the reliability of the collection system in the overall availability assessment. However, this increases the number of components significantly, introducing the dimension curse. This combined with wind turbine output dependence makes the inclusion of the collection system in OWF availability assessment computationally intractable. An analytical reliability model based on the UGF technique is proposed accounting for the cable network dependency. Further, the impact of modelling wind farm components using a binary Markov model rather than a multi-state one is also investigate

Optimal configuration of a power grid system with a dynamic performance sharing mechanism

Performance sharing is an effective policy for a power grid system to satisfy the power demand of different districts to greatest extent. Through transmission lines, the districts with sufficient power can share the redundant power with the districts with power deficit. The existing research has incorporated the performance sharing mechanism into systems with simple structures such as parallel systems and series-parallel systems. However, little concentration has been spent on more complex structures. This necessitates the need of this paper that models a power distribution with a more complex reliability structure. We assume that the system is composed of generators and nodes. Both the performance of each generator and the demand of each node in the network are assumed to be random variables. This paper first proposes a dynamic performance sharing policy to minimize the unsupplied demand for a given system with fixed capacity and demand. The optimal allocation of generators, which minimizes the expected system unsupplied demand, is then studied. Numerical examples are proposed to illustrate the applications of the proposed procedures