The effective maintenance scheduling of power system generators is very important to a power utility for the economical and reliable operation of a power system. Many mathematical methods have been implemented for generator maintenance scheduling (GMS). However, these methods have many limitations and require many approximations. Here a Genetic Algorithm is proposed for GMS problems in order to overcome some of the limitations of the conventional methods. This paper formulates a general GMS problem using a reliability criterion as an integer programming problem, and demonstrates the use of GAs with three different problem encodings: binary, binary for integer and integer. The GA performances for each of these representations are analysed and compared for a test problem based on a practical power system scenario. The effects of different GA parameters are also studied. The results show that the integer GA is a very effective method for GMS problems.

This thesis focuses on the challenges that arise from the scheduling of heat exchanger network maintenance problems which undergo fouling and run continuously over time. The original contributions of the current research consist of the development of novel optimisation methodologies for the scheduling of cleaning actions in heat exchanger network problems, the application of the novel solution methodology developed to other general maintenance scheduling problems, the development of a stochastic programming formulation using this optimisation technique and its application to these scheduling problems with parametric uncertainty. The work presented in this thesis can be divided into three areas. To efficiently solve this non-convex heat exchanger network maintenance scheduling problem, new optimisation strategies are developed. The resulting contributions are outlined below. In the first area, a novel methodology is developed for the solution of the heat exchanger network maintenance scheduling problems, which is attributed towards a key discovery in which it is observed that these problems exhibit bang-bang behaviour. This indicates that when integrality on the binary decision variables is relaxed, the solution will tend to either the lower or the upper bound specified, obviating the need for integer programming solution techniques. Therefore, these problems are in ac- tuality optimal control problems. To suitably solve these problems, a feasible path sequential mixed integer optimal control approach is proposed. This methodology is coupled with a simple heuristic approach and applied to a range of heat exchanger network case studies from crude oil refinery preheat trains. The demonstrated meth- odology is shown to be robust, reliable and efficient. In the second area of this thesis, the aforementioned novel technique is applied to the scheduling of the regeneration of membranes in reverse osmosis networks which undergo fouling and are located in desalination plants. The results show that the developed solution methodology can be generalised to other maintenance scheduling problems with decaying performance characteristics. In the third and final area of this thesis, a stochastic programming version of the feasible path mixed integer optimal control problem technique is established. This is based upon a multiple scenario approach and is applied to two heat exchanger network case studies of varying size and complexity. Results show that this methodology runs automatically with ease without any failures in convergence. More importantly due to the significant impact on economics, it is vital that uncertainty in data is taken into account in the heat exchanger network maintenance scheduling problem, as well as other general maintenance scheduling problems when there is a level of uncertainty in parameter values.

The operation of a large and complex electric power system requires meticulous and rigorous study and incessant planning. All the players involved, must plan ahead to account for the uncertainties that can affect the hour-to-hour, day-to-day, medium-term and long-term supply of electricity. Medium-term operations and planning provides the players with guidelines and strategies for short-term operating decisions vis-à-vis the market. Adequate planning helps the players to mitigate or be prepared for unforeseen circumstances encountered during scheduling of electricity generation at any stage. This thesis focuses on some aspects of the least explored medium-term operations and planning issues in power systems in the deregulated electricity market environment. The issues addressed in the thesis are diverse but inter-linked as medium-term problems, which have surfaced due to deregulation or are outcomes of unique thought-processes emerging from the restructuring phenomenon. The thesis presents a novel approach to security coordinated maintenance scheduling in deregulation wherein the ISO does not generate a maintenance schedule by itself, but assesses the maintenance schedules from individual gencos by incorporating them in a medium-term security constrained production scheduling model, and verifying whether they result in unserved energy at one or more buses. Based on the information on bus-wise unserved energy, the ISO generates corrective signals for the genco(s), and directs them to alter their maintenance schedules in specific periods and re-submit. The proposed scheme exploits the concept of commons and domains to derive a novel factor to allocate the unserved energy at a bus to a set of generators responsible. The coordination scheme is based on individual genco’s accountability to unserved energy at a bus. Another important question addressed in the thesis is whether there is a need to consider customer’s locations in the power system when the utility provides service to them. In other words, whether the reliability of the load service provided by the utility varies across the system, from bus to bus, and if so, how are the Locational Marginal Prices (LMPs), which are determined from market auctions, affected by such variations. The thesis also answers the important question of how the LMPs can be differentiated by the Load Service Probability (LSP) at a particular location, so that it is fair to all customers. A new approach to determining the bus-wise LSP indices in power systems is proposed in the thesis. These LSP indices are arrived at by defining and computing bus-wise Loss of Load Probability (LOLP) indices. The discrepancy in LMPs with respect to the bus-wise LSP is then investigated and the bus-wise LSP indices are thereafter utilized to formulate a novel proposition for LSP-differentiated LMPs for electricity markets. The thesis furthermore addresses the medium-term Transmission Reinforcement Planning (TRP) problem and proposes a practical approach to TRP by making use of standard design practices, engineering judgement, experience and thumb-rules to construct a Feasibility Set. The Feasibility Set helps in limiting the type and number of reinforcement options available to the transmission planner in selected existing corridors. Mathematical optimization procedure is then applied considering the Feasibility Set, to attain an optimal set of reinforcement decisions that are economical and meets the system demand in the medium-term, without overloading the transmission system. Two different solution approaches- the Decomposition Approach and the Unified Approach are proposed to solve the TRP optimization problem.

The operation of a large and complex electric power system requires meticulous and rigorous study and incessant planning. All the players involved, must plan ahead to account for the uncertainties that can affect the hour-to-hour, day-to-day, medium-term and long-term supply of electricity. Medium-term operations and planning provides the players with guidelines and strategies for short-term operating decisions vis-à-vis the market. Adequate planning helps the players to mitigate or be prepared for unforeseen circumstances encountered during scheduling of electricity generation at any stage. This thesis focuses on some aspects of the least explored medium-term operations and planning issues in power systems in the deregulated electricity market environment. The issues addressed in the thesis are diverse but inter-linked as medium-term problems, which have surfaced due to deregulation or are outcomes of unique thought-processes emerging from the restructuring phenomenon. The thesis presents a novel approach to security coordinated maintenance scheduling in deregulation wherein the ISO does not generate a maintenance schedule by itself, but assesses the maintenance schedules from individual gencos by incorporating them in a medium-term security constrained production scheduling model, and verifying whether they result in unserved energy at one or more buses. Based on the information on bus-wise unserved energy, the ISO generates corrective signals for the genco(s), and directs them to alter their maintenance schedules in specific periods and re-submit. The proposed scheme exploits the concept of commons and domains to derive a novel factor to allocate the unserved energy at a bus to a set of generators responsible. The coordination scheme is based on individual genco’s accountability to unserved energy at a bus. Another important question addressed in the thesis is whether there is a need to consider customer’s locations in the power system when the utility provides service to them. In other words, whether the reliability of the load service provided by the utility varies across the system, from bus to bus, and if so, how are the Locational Marginal Prices (LMPs), which are determined from market auctions, affected by such variations. The thesis also answers the important question of how the LMPs can be differentiated by the Load Service Probability (LSP) at a particular location, so that it is fair to all customers. A new approach to determining the bus-wise LSP indices in power systems is proposed in the thesis. These LSP indices are arrived at by defining and computing bus-wise Loss of Load Probability (LOLP) indices. The discrepancy in LMPs with respect to the bus-wise LSP is then investigated and the bus-wise LSP indices are thereafter utilized to formulate a novel proposition for LSP-differentiated LMPs for electricity markets. The thesis furthermore addresses the medium-term Transmission Reinforcement Planning (TRP) problem and proposes a practical approach to TRP by making use of standard design practices, engineering judgement, experience and thumb-rules to construct a Feasibility Set. The Feasibility Set helps in limiting the type and number of reinforcement options available to the transmission planner in selected existing corridors. Mathematical optimization procedure is then applied considering the Feasibility Set, to attain an optimal set of reinforcement decisions that are economical and meets the system demand in the medium-term, without overloading the transmission system. Two different solution approaches- the Decomposition Approach and the Unified Approach are proposed to solve the TRP optimization problem.

Thesis deals with the topic of computational scheduling of production with dynamic reconfigurations and maintenance. The problem is formally defined by a mathematical model named Resource Constrained Project Scheduling Problem which was extended by dynamic reconfiguration and maintenance. Number of different schedule generation algorithms were proposed based on this model. Also methods of solution optimization based on genetic algorithms were described. The typology of production orders of which different task types are created was described in the experimental part. The result of the experiments is clear recommendation of scheduling algorithm for given task type. For the conclusion, thesis deals with the case study of choice of suitable solution for specific production companies.

[pt] O uso de ferramentas de otimização destaca-se como um relevante diferencial para as empresas no que tange a otimização de processos e melhoria de sistemas e performances. Neste contexto, a busca por modelos de programação simples e eficazes para a resolução dos problemas contribuem para adaptação de modelos existentes a fim de atender a esta crescente demanda. Atualmente, o setor de transporte ferroviário busca otimização de seus processos com o objetivo de aumentar sua competitividade e eficiência frente ao transporte realizado por rodovia. Este estudo, focado na melhoria de processos do setor ferroviário, tem como objetivo realizar o planejamento da distribuição de materiais de manutenção em uma malha ferroviária com o menor custo operacional viável. Para isto, o problema é modelado como um problema de programação inteira mista e busca tornar o processo mais eficiente, com redução de desperdícios e otimização dos recursos. Os resultados obtidos foram comparados ao processo atual de distribuição a fim de medir os ganhos em processo e em redução de custos e recursos. O modelo se mostrou eficiente em tempo e qualidade de solução quando comparado com o atual, apresentando uma redução de 20 por cento a 26 por cento nos custos totais de distribuição, variando de acordo com o almoxarifado analisado. Além disso, o estudo também mostrou uma redução no custo de distribuição para todas as localidades testadas, sendo que, quanto menor a distância destes locais ao almoxarifado, maior a redução dos custos logísticos relacionados. / [en] The use of optimization tools highlights a relevant differential to companies in terms of improving processes, systems and performance. In this context, the search for simple and effective programming models for problem solving contributes to the adaptation of existing models to attend this increasing demand. Currently, the railway transport seeks to optimize its processes in order to increase its competitiveness and efficiency when compared to road transport. This study, focused on improving processes in the railway, aims to realize the distribution planning of maintenance materials in a railway network with the lowest feasible operating cost. For this, the problem is modeled as a mixedinteger programming problem and it aims to make the process more efficient, with waste reduction and resource optimization. The obtained results were compared to the current distribution process in order to measure gains in process and in reducing costs and resources. The model proved to be efficient in both time and solution quality when compared to the current one, presenting a reduction of 20 percent to 26 percent in the distribution costs, depending on the analyzed warehouses. In addition, the study has also indicated a reduction in the distribution costs in all tested locations and the distance among those locations and their warehouses leads to a greater reduction in the logistic costs.

[pt] No sistema elétrico de potência podem ocorrer falhas que resultarão na interrupção do fornecimento de energia para os consumidores conectados a esses sistemas. Uma concessionária de energia elétrica deve prestar aos seus clientes um serviço que seja confiável e de boa qualidade. Por isso, o planejamento seguro e eficiente se faz necessário para obter a confiabilidade do sistema elétrico de acordo com as exigências estabelecidas pela agência reguladora do setor, onde caso não sejam observadas pela distribuidora de energia são cabíveis de punições monetárias. O desempenho de um sistema pode ser observado com base no histórico de interrupções, por meio dos indicadores de continuidade. A baixa flexibilidade operativa de subestações aliada à configuração das redes reduz a confiabilidade dos sistemas, causando prejuízos às empresas e aos consumidores por estarem vulneráveis e sofrerem interrupções de energia. O presente estudo é essencial, pois visa identificar métodos e análises apuradas que indiquem os pontos prioritários para manutenções nas redes elétricas. Dessa forma, a dissertação apresenta uma metodologia que identifica os equipamentos e trechos associados aos pontos críticos e de maior impacto em uma rede de distribuição. A partir daí é possível direcionar os serviços de manutenção dos circuitos para os trechos de maior impacto nos indicadores de continuidade de uma determinada região e otimizar o orçamento correspondente. A ferramenta usada para analisar os indicadores é uma matriz de risco, onde os eixos representam probabilidade de ocorrência (reincidência) e impacto corporativo (índice de continuidade) de modo a capturar mais precisamente os pontos para atuações de manutenção prioritária. Desenhada a estrutura da matriz, os fatores de risco identificados são avaliados qualitativamente, em termos de probabilidade e impacto, e posicionado na matriz, indicando seu estado: eminente, crítico, alto, médio e baixo. São analisados dois sistemas de distribuição reais da classe de 13,8 kV, com o objetivo de demonstrar a capacidade da metodologia de encontrar as soluções condizentes do ponto de vista técnico e econômico. Os resultados apontam uma redução dos indicadores de continuidade, colaborando assim na eficaz gestão do sistema elétrico e na mitigação dos prejuízos econômicos associados às interrupções de energia. / [en] Faults can occur in the electrical power system which will result in interruption of the power supply to consumers connected to these systems. An electric power utility should provide its customers with a service that is reliable and of good quality. Therefore, safe and efficient planning is necessary to obtain the reliability of the electrical system according to the requirements established by the regulatory agency of the sector. In case they are not observed by the electrical energy distributor, monetary penalties are possibly applied. The performance of a system can be observed based on the history of interruptions, through the continuity indicators. The low operational flexibility of substations, coupled with the network configurations, reduces the reliability of the systems causing monetary damage to companies and consumers, due to their vulnerability to interruptions of energy. The present study is essential because it aims to identify methods and analysis that detect the priority points for maintenance in the electric networks. In this way, the dissertation presents a methodology that identifies the equipment and sections associated to the critical points of greater impact in a distribution network. Thus, it is possible to direct the maintenance services of the circuits to the segments of greater impact in the indices of continuity of a certain region and to optimize the corresponding budget. The basic tool used to analyze the indices is a risk matrix, where the axes represent the probability of occurrence (recurrence) and company impact (continuity indices), in order to capture more precisely the points for priority maintenance actions. When the matrix structure is established, the identified risk factors are qualitatively assessed in terms of probability and impact, and positioned in the matrix, indicating their state: eminent, critical, high, medium, and low. Two real distribution systems of the 13.8 kV class are analyzed to demonstrate the ability of the proposed methodology to find the appropriate solutions from a technical and economic point of view. The results point to a reduction in continuity indicators, thus contributing to the effective management of the power electric system and mitigating the economic losses associated with power outages.

Change from a regulated to deregulated structure means that, the centralized maintenance system is not valid any more. In the surveyed published literature, there is not a single model which incorporates all maintenance cost components to analyze the effect of different maintenance strategies for generator companies (GENCOs). The work enclosed in this thesis demonstrates that there is a considerable requirement for accurately modelling cost components of the maintenance model, to be used in maintenance scheduling for deregulated power system, in order to attain a superior schedule with major financial and operational impact. This research investigates and models most cost factors that affect the maintenance activities of the deregulated GENCOs, and demonstrates the utilization of the developed cost models in maintenance scheduling. It also presents the data gathering process for the developed maintenance cost model. A generator maintenance scheduling model that considers direct and indirect maintenance costs, opportunity costs (i.e. loss of customer goodwill), effective maintenance strategies, failures, and interruptions is developed. A Genetic Algorithm (GA) based approach is employed to achieve maintenance schedules to various generators maintenance scenarios. An Analytical Hierarchy Process (AHP) approach is proposed for modelling customer goodwill. The maintenance model was redeveloped under the Reliability Centred Maintenance (RCM) strategy to analyze the effect of a maintenance strategy on maintenance costs. Case studies are presented to demonstrate the utilisation of the developed models.The investigation shows that the market prices, opportunity costs and maintenance strategy have an effect on the final maintenance schedule. The research demonstrates that the cost components are critical factors to achieve an effective maintenance schedule, and they must be considered and carefully modelled in order to reflect more realistic situation for maintenance scheduling of generator units in deregulation environment.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The demand for rail travel has increased over the years. As a result, it is becoming mandatory for railway industries to maintain very high availability of their assets to ensure that service levels are high. Railway industries require both their infrastructure and rolling stock assets maintained efficiently to sustain reliability. There has been on-going research on how maintenance can be carried out in a cost effective manner. However, the majority of this research has been done for infrastructure and the rolling stock maintenance has not been properly covered. The purpose of this research is to contribute to the maintenance sector of rolling stock for railway industries by developing a decision support model for rolling stock based on reliability and cost. The model is developed as an optimization problem of a system containing several components dependent on each other with different reliability characteristics. In this model, a mixed integer nonlinear problem is developed and solved using an exact method and metaheuristics methods. The Metrorail facility in Cape Town was chosen as a case study. Failure history and cost data were gathered from the facility and the information was applied to the model developed. The case study was investigated and different results were achieved using both exact and metaheuristics methods. The final result from the study is an optimal maintenance schedule based on reliability and cost. The developed model serves as a practical tool railway companies can adopt to schedule rolling stock maintenance to achieve a high level of reliability and at the same time maintaining minimum cost expenditure. / AFRIKAANSE OPSOMMING: Die vraag na spoorvervoer het oor die jare toegeneem. Dus het dit belangrik geword dat die spoorweg se bates hoogs toeganklik moet wees om te verseker dat die vlak van dienslewering hoog bly. Die spoorweg industrie besef dat hulle infrastruktuur, lokomotiewe, waens ens. effektief in stand gehou moet word sodat dit betroubaar kan wees. Navorsing word nog steeds gedoen oor hoe instandhouding op ’n koste-effektiewe wyse gedoen kan word. Die meeste van hierdie navorsing gaan egter oor infrastruktuur en instandhouding word nie ordentlik gedek nie. Die doel met hierdie navorsing is om by te dra tot die instandhoudingsektor van die spoorweg deur om ’n besluit-ondersteunende model vir lokomotiewe, waens, ens wat op betroubaarheid en koste gegrond is, te ontwikkel. Die model is ontwikkel as ’n optimasie probleem van ’n sisteem wat verskillende komponente wat van mekaar afhanklik is maar oor verskillende betroubaarheidskenmerke beskik, inluit. In hierdie model word ’n gemengde, heeltal nie-lineêre probleem ontwikkel en met ’n eksakte metode en metaheuristiese metodes opgelos. Die Metrorail fasiliteit in Kaapstad is vir die gevalle studie gekies. Die geskiedenis van mislukkings en koste data is by die fasiliteit versamel en die inligting is op die model wat ontwikkel is, toegepas. Die gevalle studie is ondersoek, en verskillende resultate is met eksakte en metaheuristiese metodes bereik. Die finale uitkomste van die studie is ’n optimale instandhoudingskedule wat op betroubaarheid en koste gegrond is. Die model wat ontwikkel is dien as ’n praktiese instrument wat spoormaatskappye kan gebruik om die instandhouding van lokomotiewe, waens ens. te reël sodat ’n hoë vlak van betroubaarheid bereik kan word en kostes terselfdertyd tot ’n minimum beperk kan word.

Effective maintenance planning is essential and important in any organisation that is responsible for procuring and managing complex assets. In the marine shipping industry maintenance planning is very significant due to its complexity and the obligations on shipping organisations to comply with certain regulations and requirements. Moreover, improper planning can reduce the ship's availability, which may in turn, be reflected in the revenue of the company. Another issue that requires attention in this field is the cost of maintenance, since improper or inadequate planning could result in breakdowns that could increase the cost of maintenance.This research aims to identify the key factors that affect ship maintenance planning and to provide a framework that can help the decision maker to identify and choose optimum decisions regarding ship maintenance. The research is divided into four stages in order to achieve its objectives and to address the research problem.The first stage is the review of the literature to identify the need for maintenance and to select the key factors that affect maintenance planning. The findings indicate that: maintenance scheduling, selection of maintenance strategy, ship construction, crew compensation, and shipyard selection are the most important factors.The second stage is to evaluate maintenance performance measurements for the marine shipping industry by conducting case study and interviews with professionals involved in the mercantile industry. Semi-structured interviews were conducted with six senior staff experts from three different organisations. The results show that: dry docking scheduling, maintenance costs and budgets, customer satisfaction, employees' satisfaction, classification requirements, and the ship's maintenance requirements are the main factors that have great influence on maintenance planning.The third stage is to develop new methodology to measure the maintenance performance in the marine shipping organisation which is the ship maintenance performance measurement (SMPM) framework. The developed method was validated to assist managers in making the right decisions in ship maintenance planning. The framework was developed based on ten thematic criteria that can be used as indicators for potential organisation growth, i.e., maintenance strategy; dry docking scheduling; budget and costs; the ship's equipment; customer satisfaction; employees; health, safety and environment; learning and growth; classification requirements; and the ship's operation and demands requirements. Interviews were conducted with key personnel from the Kuwait Oil Tanker Company (KOTC) to validate the framework.The fourth stage demonstrates that an optimised schedule for the dry docking of ships for routine maintenance has been constructed. This is accomplished on the basis of one measured criterion, dry docking scheduling, by using an integer programming model to maximise the ship's availability within the company fleet. The model is defined by three constraints: the maintenance window, maintenance completion, and the ship's limit. The model was validated using data from KOTC, and the results depict an optimum solution for maintenance scheduling, maximising the ship's availability to 100% and not less than 92%.