Reliability of multi-channel IEC 61850 mission-critical substation communication networks based on Markov process incorporating linear dynamical systems and calculus inferences.

Doctoral Degree. University of KwaZulu-Natal, Durban.IEC 61850 based Substation Communication Networks (SCN) enable substation processes to be digitalised to fulfil the most sought substation monitoring, protection and control of electrical systems. The standard enables peer-to-peer communication of mission critical messages, aided by onboard diagnostic capabilities to ease the identification of system faults. The implementation of Safety-Related Systems in industrial facilities comprising sensors, logic solvers and final elements in power distribution centres necessitate compliance to IEC 61508 standard, where circuit breakers act as final elements to isolate electrical machines. In recent times, combinatorial methods such as the Reliability Block Diagram have been used to evaluate the architecture of IEC 61850 based SCN reliability and availability due to the simplicity of the approach. These methods, however, assume that all system faults are identified and fully repaired, which is not the case in practice. In this thesis, the reliability of a repairable multi-channel IEC 61850 based SCN architecture is modelled using a structure function and the Markov process while Systems Thinking integrates imperfect repair factors into the model. Thereafter, a novel eigenvalue analysis method based on Markov partitions and symbolic dynamics in the context of linear dynamical systems is used to investigate the impact of imperfect repairs on the system's reliability based on the number of mean state transitions and dynamical behaviour. The eigenvalue method is then advanced by a complimentary analysis technique based on the absorbing Markov Chain process and matrix calculus methods to determine the system's responsiveness to repair factors. The case studies results demonstrate that imperfect repairs cannot be ignored for mission-critical applications because the simplifying assumptions of combinatorial analysis methods greatly over-state the system's reliability performance. The results also indicate that common causes of failure coupled with imperfect repairs significantly negatively impact the system's performance. Moreover, system performance is highly dependent on the diagnostic coverage of the individual subsystems than their repair efficiencies for high diagnostic coverages at 90% and 99% based on ISO 13849-1. Hence, the results demonstrate that emphasis should be more on the system diagnostic coverage for the fact that it is embedded in the system design itself that cannot easily be changed once the system is commissioned and operational

Diagnostic Applications for Micro-Synchrophasor Measurements

This report articulates and justifies the preliminary selection of diagnostic applications for data from micro-synchrophasors (µPMUs) in electric power distribution systems that will be further studied and developed within the scope of the three-year ARPA-e award titled Micro-synchrophasors for Distribution Systems

Technology assessment of advanced automation for space missions

Six general classes of technology requirements derived during the mission definition phase of the study were identified as having maximum importance and urgency, including autonomous world model based information systems, learning and hypothesis formation, natural language and other man-machine communication, space manufacturing, teleoperators and robot systems, and computer science and technology

Validation Methods for Fault-Tolerant avionics and control systems, working group meeting 1

The proceedings of the first working group meeting on validation methods for fault tolerant computer design are presented. The state of the art in fault tolerant computer validation was examined in order to provide a framework for future discussions concerning research issues for the validation of fault tolerant avionics and flight control systems. The development of positions concerning critical aspects of the validation process are given

Fault detection and correction modeling of software systems

Ph.DDOCTOR OF PHILOSOPH

Fault-tolerant hardware designs and their reliability analysis

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Fault-tolerance, which is a complement to fault prevention, is an effective method of achieving ultra-high reliability. By taking this approach fault free computation can be achieved despite the presence of fault in the system. In this thesis three new fault tolerant techniques are presented and their advantages over well known fault-tolerant strategies are shown. One of these new techniques achieves higher reliability than any other similar techniques presented in the literature. Generally fault-tolerant structures consist of four major blocks: the replicated modules, the disagreement and detection circuit, the switching circuit, and the voting mechanism. The most critical component in a fault-tolerant system is the voter because the final output of the system is computed by this component. This dissertation presents a new implementation for voters which reduces both the complexity and the occupied area on the chip. The structures of the three techniques developed in this work are such that the complexity of their switching mechanisms grows only linearly with the number of modules but the voting mechanism complexity increases significantly. This is a better approach than those schemes in which the switching complexity increases significantly and the voter's complexity remains constant or grows linearly with the number of modules because it is easier to implement a complex voter than a complex switch (voters have more regular structures). Extensive comparisons are made between different fault-tolerant techniques. A new reliability model is also developed for system reliability evaluation of the new designs. The results of these analyses are plotted, and the advantages of the new techniques are demonstrated. In the final part of the work an expert system is described which uses the knowledge acquired by these comparisons. This expert system is meant as a prototype of a component of a CAD tool which will act as an advisor on fault-tolerant techniques

Integrated Systems Health Management as an Enabler for Condition Based Maintenance and Autonomic Logistics

Health monitoring systems have demonstrated the ability to detect potential failures in components and predict how long until a critical failure is likely to occur. Implementing these systems on fielded structures, aircraft, or other vehicles is often a struggle to prove cost savings or operational improvements beyond improved safety. A system architecture to identify how the health monitoring systems are integrated into fielded aircraft is developed to assess cost, operations, maintenance, and logistics trade-spaces. The efficiency of a health monitoring system is examined for impacts to the operation of a squadron of cargo aircraft revealing sensitivity to and tolerance for false alarms as a key factor in total system performance. The research focuses on the impacts of system-wide changes to several key metrics: materiel availability, materiel reliability, ownership cost, and mean downtime. Changes to theses system-wide variables include: diagnostic and prognostic error, false alarm sensitivity, supply methods and timing, maintenance manning, and maintenance repair window. Potential cost savings in maintenance and logistics processes are identified as well as increases in operational availability. The result of this research is the development of a tool to conduct trade-space analyses on the effects of health monitoring techniques on system performance and operations and maintenance costs

Enrichment of Wind Turbine Health History for Condition-Based Maintenance

This research develops a methodology for and shows the benefit of linking records of wind turbine maintenance. It analyses commercially sensitive real-world maintenance records with the aim of improving the productivity of offshore wind farms. The novel achievements of this research are that it applies multi-feature record linkage techniques to maintenance data, that it applies statistical techniques for the interval estimation of a binomial proportion to record linkage techniques and that it estimates the distribution of the coverage error of statistical techniques for the interval estimation of a binomial proportion. The main contribution of this research is a process for the enrichment of offshore wind turbine health history. The economic productivity of a wind farm depends on the price of electricity and on the suitability of the weather, both of which are beyond the control of a maintenance team, but also on the cost of operating the wind farm, on the cost of maintaining the wind turbines and on how much of the wind farm’s potential production of electricity is lost to outages. Improvements in maintenance scheduling, in condition-based maintenance, in troubleshooting and in the measurement of maintenance effectiveness all require knowledge of the health history of the plant. To this end, this thesis presents new techniques for linking together existing records of offshore wind turbine health history. Multi-feature record linkage techniques are used to link records of maintenance data together. Both the quality of record linkage and the uncertainty of that quality are assessed. The quality of record linkage was measured by comparing the generated set of linked records to a gold standard set of linked records identified in collaboration with offshore wind turbine maintenance experts. The process for the enrichment of offshore wind turbine health history developed in this research requires a vector of weights and thresholds. The agreement and disagreement weights for each feature indicate the importance of the feature to the quality of record linkage. This research uses differential evolution to globally optimise this vector of weights and thresholds. There is inevitably some uncertainty associated with the measurement of the quality of record linkage, and consequently with the optimum values for the weights and thresholds; this research not only measures the quality of record linkage but also identifies robust techniques for the estimation of its uncertainty.