The overall reliability of a power transformer depends to a great extent on the sound operation of the bushings thereof. In view of its overwhelming advantages, resin impregnated paper (RIP) is acquiring prominence over conventional oil impregnated paper (OIP) in transformer bushings. The main advantages of RIP bushings are low dielectric loss and capability of positioning them at any desired angle over the transformer. The RIP structure, being an all-solid system, is completely free from oil phase. The temperature rise in RIP bushings under normal operating conditions is seen to be a difficult parameter to control in view of the limited options for effective cooling. The degradation of dry-type insulation such as RIP is often due to thermal and electrical stresses. The long time performance thereof, depends strongly, on the maximum operating temperature. In order to be able to predict the regional temperature, it is necessary to consider the thermal and electrical parameters of insulation in question; and to identify and solve the governing equations under the relevant boundary conditions. Electrical failure of insulation is known to be an extremal random process wherein nominally identical specimens of equipment insulation, at constant stress fails at inordinately different times. In order to be able to estimate the life of power equipment like transformer bushing, it is necessary to run long duration ageing experiments under accelerated stresses, to acquire and analyze insulation specific failure data. The present work is an attempt to provide reliability and life estimation of High Voltage RIP bushing insulation. The literature survey carried out in this view indicate that investigation on thermal and electric field distribution and the models for failure under combined stress and analysis of the data so as to be able to estimate the possible life of RIP bushing is scanty. Having these aspects in focus, the scope of the present work is defined as: (i) Mapping of the temperature and electric field distribution in the body of 400kV RIP bushing (ii) Deduction of parameters of the probabilistic models for the failure under electrical and thermal ageing (iii) Estimation of life based on diagnostic testing using PD With this in view, the temperature distribution in the body of a 400kV RIP bushing is studied considering the heat generation both in central conductor and that in the insulation. Presence of multiple materials with non-confirming interfaces makes analytical solution rather difficult and hence numerical approach is adopted. In the present work, vertex-centered Finite Volume Method (FVM) is employed for both thermal and electrical analysis. The electric stress distribution is accurately evaluated considering both the non-zero conductivity of the RIP material and the presence of capacitive grading foils. These analysis has clearly shown that Stress grading foils uniforms the stress across the major portion of the bushing insulation Enhancement of the electric conductivity by the temperature is not found to be affective in changing the electric field distribution The temperature distribution is shown to have a maxima near the flange due to the influence of top oil temperature of the transformer Heat generated in the dielectric due to the prevailing electric stress is shown to be insignificant. This ruled out the possibility of thermal runaway and hence the dielectric temperature is within the safe working limits for the bushing considered. The deduction of physical models governing insulation failure depends on the nature of stress. In this work, the insulation failure at constant accelerated stress has been considered and the estimation of life is computed based on inverse power law coupled with Arrhenius law. A high degree of scatter is generic to the experimental data forming the ingredients to develop the models. In view of this, the concept of a random process is invoked. Probabilistic models for the failure of RIP bushing under synergy are adopted and an attempt is made to estimate the life. The well known Weibull distribution and probability plotting of life data is used in this endeavor. The maximum likelihood estimation is used to determine the scale and shape parameters of the Weibull distribution. In the diagnosis of the extent of degradation of insulation due to PD, under long duration electric stress, a non-conventional voltage application method called the classical stepped stress method is adopted. In this technique, the voltage is applied in pre-determined steps over predetermined duration of time. The magnitude of voltage steps is carefully computed based on Miners law and the end-of-life is computed using inverse power law. In summary, this thesis work has contributed to the thermal and electrical degradation of resin impregnated paper insulation for high voltage transformer bushing. The thermal and electrical field distributions computed in the body of bushing clearly shown that these stresses are well within the limit, thereby ruling out the possibility of a thermal runaway. Comparing the estimates of the most probable life of RIP, based on several methods appears to show that any of the method can be adopted. However, as matter of caution and safety, the lowest among them can be taken as a reasonable estimate.

The goal of the project was to create a model in COMSOL Multiphysics that can simulate thefilling of resin (epoxy) in Resin Impregnated Paper (RIP) bushings. Using the model new fillingrecipes that avoid problematic double-fronts and thereby avoid the creation of cavities in thebushings should be designed. Another goal was to use Thermocouples and Fiber optics tomeasure the temperature at different positions during the filling to get a better understanding ofthe filling. The first step was to design and determine functions, parameters (such as thepermeability), boundary conditions etc. for the simulation model in COMSOL Multiphysics and tocalibrate the model to align with measurements of fillings previously done. The second part wasto increase the filling time to minimize the maximum difference between filling fronts in thebushings and thereby decrease the risk of problematical double-fronts that create cavities,which decrease the bushing's dielectrical properties. The simulation model aligned somewhatwith the measured data but there is a lot of uncertainty both in the measurements and due toassumptions made in the simulation model. The measurements from Thermocouples and Fiberoptics where almost identical and they indicated that the filling of the bushing is symmetric.

This dissertation is a study of artificial intelligence for diagnosing the condition of high voltage bushings. The techniques include neural networks, genetic algorithms, fuzzy set theory, particle swarm optimisation, multi-classifier systems, factor analysis, principal component analysis, multidimensional scaling, data-fusion techniques, automatic relevance determination and autoencoders. The classification is done using Dissolved Gas Analysis (DGA) data based on field experience together with criteria from IEEEc57.104 and IEC60599. A review of current literature showed that common methods for the diagnosis of bushings are: partial discharge, DGA, tan- (dielectric dissipation factor), water content in oil, dielectric strength of oil, acidity level (neutralisation value), visual analysis of sludge in suspension, colour of the oil, furanic content, degree of polymerisation (DP), strength of the insulating paper, interfacial tension or oxygen content tests. All the methods have limitations in terms of time and accuracy in decision making. The fact that making decisions using each of these methods individually is highly subjective, also the huge size of the data base of historical data, as well as the loss of skills due to retirement of experienced technical staff, highlights the need for an automated diagnosis tool that integrates information from the many sensors and recalls the historical decisions and learns from new information. Three classifiers that are compared in this analysis are radial basis functions (RBF), multiple layer perceptrons (MLP) and support vector machines (SVM). In this work 60699 bushings were classified based on ten criteria. Classification was done based on a majority vote. The work proposes the application of neural networks with particle swarm optimisation (PSO) and genetic algorithms (GA) to compensate for missing data in classifying high voltage bushings. The work also proposes the application of fuzzy set theory (FST) to diagnose the condition of high voltage bushings. The relevance and redundancy detection methods were able to prune the redundant measured variables and accurately diagnose the condition of the bushing with fewer variables. Experimental results from bushings that were evaluated in the field verified the simulations. The results of this work can help to develop real-time monitoring and decision making tools that combine information from chemical, electrical and mechanical measurements taken from bushings.

The aim in this project is to find a design space for a condenser type bushing given by HitachiEnergy. The design space shows which combinations of air and silicon-rubber (SiR) conductivity remain under a specified electric field strength value. This range of value represents how humidity affects air and SiR conductivity. Hitachi energy provided two different models, one with foils and one without foils. The design space for these models consists of how humidity affects the conductivity of both air and SiR. The values of air conductivity are gathered from different studies with different air humidity and external effects that affect the conductivity such as high aerosol concentration and high radon concentration. The values used for simulation will be approximated because of the different external effects and will range from 10^(−12)–10^(−13) S/m for humid conditions, 10^(−14) S/m for average humidity conditions and 10^(−15)–10^(−16) S/m for dry conditions. The range of SiR conductivity and the correlated weather conditions was given by Hitachi Energy and range from 10^(−11)–10^(−15) S/m where 10^(−11) S/m is for humid conditions, 10^(−12)–10^(−14) S/m for average humidity conditions and 10^(−15) S/m for dry conditions. For each of these combinations of conductivity the maximum electric field strength is calculated using COMSOL Multiphysics and compared to the threshold value of 2 kV/mm. Using these parameters the maximum electric field strength on the sheds of the bushing was calculated using COMSOL Multiphysics for all combinations of SiR and air conductivity. The results shows a pattern for both models. SiR conductivity must be higher or equal to the air conductivity to be below the threshold of 2 kV/mm.

Les articulations en caoutchouc naturel sont des éléments indispensables et nombreux dans une liaison au sol automobile afin d'assurer le filtrage des vibrations. Leur comportement non-linéaire, notamment visco-élastique et hystérétique engendrent cependant des phénomènes parfois indésirables ou imprévus qui peuvent impacter la dynamique du véhicule. Ce travail a permis de modéliser l'ensemble des comportements d'une articulation en caoutchouc grâce à un nouveau modèle, le modèle STVS ( Standard Triboelastic Visco Solid) inspiré des travaux sur le génie parasismique et notamment du modèle STS (Standard Triboelastic Solid) de V. Coveney. L'identification d'un tel modèle non-linéaire a été envisagée de différentes façons : empirique, d'après des données fréquentielles. Les bases d'une identification d'après des données temporelles sont également posées. L'introduction d'un modèle d'articulation identifié sur des mesures dans une simulation transitoire multi-corps de liaison au sol d'un véhicule permet de mettre en évidence des phénomènes qui jusqu'à présent n'étaient pas représentés par une simple élasticité, comme des effets de relaxation des articulations lors d'un échelon d'angle au volant, ou l'impact des différentes amplitudes de sollicitations. / Rubber bushings are necessary elements to filtrate undesirable vibrations in vehicle chassis. They are numerous and their non linear behaviour like viscoelasticity or hysteresis generate phenomenon which can influence the vehicle dynamics. This study describes a new model for rubber bushings, representative for all their temporal mechanical behaviours. This model Is called STVS ( Standard Triboelastic Visco Solid). The identification of such a non-linear temporal model has been studied through different viewpoints : empirical identification, identification based on frequency data and the grounds for a temporal dat based identification have been described. The introduction of such an identified rubber bushing model in a multi-body simulation of a vehicle chassis, unables us to point out phenomenon which could not be evidenced through a simple elasticity modelling : for instance, relaxation in bushings during a wheele angle sollicitation or the impact of different sollicitation amplitudes on the response of the bushing.

M. Ing. / Fault detection tools have gained popularity in recent years due to the increasing need for reliable and predictable equipments. Transformer bushings account for the majority of transformer faults. Hence, to uphold the integrity of the power transmission and dis- tribution system, a tool to detect and identify faults in their developing stage is necessary in transformer bushings. Among the numerous tools for bushings monitoring, dissolved gas analysis (DGA) is the most commonly used. The advances in DGA and data storage capabilities have resulted in large amount of data and ultimately, the data analysis crisis. Consequent to that, computational intelligence methods have advanced to deal with this data analysis problem and help in the decision-making process. Numerous computational intelligence approaches have been proposed for bushing fault detection. Most of these approaches focus on the accuracy of prediction and not much research has been allocated to investigate the interpretability of the decisions derived from these systems. This work proposes a rough set theory (RST) model for bushing fault detection based on DGA data analyzed using the IEEEc57.104 and the IEC 60599 standards. RST is a rule-based technique suitable for analyzing vague, uncertain and imprecise data. RST extracts rules from the data to model the system. These rules are used for prediction and interpreting the decision process. The lesser the number of rules, the easier it is to interpret the model. The performance of the RST is dependent on the discretization technique employed. An equal frequency bin (EFB), Boolean reasoning (BR) and entropy partition (EP) are used to develop an RST model. The model trained using EFB data performs better than the models trained using BR and EP. The accuracy achieved is 96.4%, 96.0% and 91.3% for EFB, BR and EP respectively. This work also pro poses an ant colony optimization (ACO) for discretization. A model created using ACO discretized achieved an accuracy of 96.1%, which is compatible with the three methods above. When considering the overall performance, the ACO is a better discretization tool since it produces an accurate model with the least number of rules. The rough set tool proposed in this work is benchmarked against a multi-layer perceptron (MLP) and radial basis function (RBF) neural networks. Results prove that RST modeling for bushing is equally as capable as the MLP and better than RBF. The RST, MLP and RBF are used in an ensemble of classifiers. The ensemble performs better than the standalone models.

High voltage bushings are the most critical components of power transformers. A common material used in bushings is resin impregnated paper (RIP). Hitachi Energy is investigating whether this can be replaced with a new material, resin impregnated non-woven (RIN). One of the main reasons is that non-woven is less prone to absorb moisture compared to paper. Thus, for design purposes the mechanical, thermal and absorption properties of RIN have been studied and compared to RIP. The mechanical properties were tested by tensile and bending tests at room temperature and 80 ℃, showing that RIN has a lower elastic modulus and tensile strength than RIP at both temperatures. However, it was demonstrated that RIN does not retain its elongation at break and elasticity properties at elevated temperatures. The bending test showed no significant differences in flexural properties for RIN between room and high temperature. The thermal properties were studied with the transient plane source method (TPS) showing that both RIN and RIP had a higher specific heat capacity than pure epoxy. The thermal conductivity of the materials will be measured and included later. Lastly, the water absorption test was performed in order to provide information about the suitability of the materials used in bushings. For this different methods were used; water immersion andwater vapor testing. The immersion test showed that non-woven is more water resistant than paper and that the composites only absorb a small amount of water. No useful information was achieved from the water vapor test due to limited testing time. The results demonstrate the promising potential of RIN in bushings.

Electrical bushings are a type of hollow or solid conductor withinsulation designed to allow a conductor to pass through a conductingbarrier without making electrical contact and are very important forsafe transportation of electricity. The bushings vary in size, but allbushings have a solid or hollow conductor.This project aims to investigate which resistivities of the siliconerubber, in combination with different air conditions for the airsurrounding the bushing (dry, average and humid air) and theirrespective resistivities, to see which combinations allow for anelectrical field that allows the bushing to safely work without beingdamaged. The different air conditions are an important factor since theyall correspond to different absolute humidities present in the air,which have a direct impact on the strength of the electrical fieldsurrounding the bushing. Since this cannot be done by hand, a computersoftware called COMSOL Multiphysics will be used. COMSOL is aMultiphysics software, meaning one can simulate many types of physics atonce. With the help of this software, and a model provided by HitachiEnergy, results could be found stating that dry air overall is the bestcondition of air for the bushing, followed by average (not either dry orhumid) air and lastly humid air.

Drawing on long-term clinical experience, the dissertation provides an overview of the options for the reconstructive surgery of irreversibly damaged elbow joints and the individual structural directions in the development of total elbow replacements. The clinical study focuses on the comparison of the unconstrained Souter-Strathclyde elbow implant, which has been used at our workplace since 1987, and the semiconstrained Coonrad-Morrey implant, which we started to use in the nineties. The disadvantages of the Souter-Strathclyde implant consist of a relatively complex surgery technique and narrower indication which does not permit larger primary instability of the operated elbow and large bone defects. Due to these reasons in recent years the Coonrad-Morrey total elbow replacement has been the preferred option at our workplace. The main problem as regards the long-term survival of this implant is especially the wear of the polyethylene bushings of the fl oppy hinge. This can be solved through an early replacement of this hinge before substantial abrasive wear develops ultimately leading to the loosening of the whole implant. We have elaborated a methodology that maps the condition of the polyethylene bushings and at the same time examines the integration of the humeral and ulnar component in the...

Drawing on long-term clinical experience, the dissertation provides an overview of the options for the reconstructive surgery of irreversibly damaged elbow joints and the individual structural directions in the development of total elbow replacements. The clinical study focuses on the comparison of the unconstrained Souter-Strathclyde elbow implant, which has been used at our workplace since 1987, and the semiconstrained Coonrad-Morrey implant, which we started to use in the nineties. The disadvantages of the Souter-Strathclyde implant consist of a relatively complex surgery technique and narrower indication which does not permit larger primary instability of the operated elbow and large bone defects. Due to these reasons in recent years the Coonrad-Morrey total elbow replacement has been the preferred option at our workplace. The main problem as regards the long-term survival of this implant is especially the wear of the polyethylene bushings of the fl oppy hinge. This can be solved through an early replacement of this hinge before substantial abrasive wear develops ultimately leading to the loosening of the whole implant. We have elaborated a methodology that maps the condition of the polyethylene bushings and at the same time examines the integration of the humeral and ulnar component in the...