Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

ELECTRIC FIELD AND CURRENT DENSITY CHARACTERISTIC OF CONTAMINATED SOLID INSULATOR

The performance of an insulator may degrade over a time period. One of the main factor is due to presence of contamination on the insulator which leads to flashover, corona and damages the insulator. This study focuses on overhead XLPE cables used in distribution system with voltage rated 33kV. The contaminants are varied in order to study the behaviour of electric field and current density of the XLPE insulator. Contaminant used in this study is sodium chloride, lead and rain water. Quickfield software was used to draw and simulate the contaminated cable. The electrical conductivity of cable and contamination was used to represent every layer of the drawing. From the result produce, analysis on the electric field and current density of a contaminated and non-contaminated insulator was made. Analysis shows that the contaminated insulator has higher electrical field and current density compared to non-contaminated insulator. When the electrical conductivity is high, the electric field is the lowest and the current density is the highest in the insulator. Whereas, the XLPE insulator with sodium chloride contamination has the highest current density followed by rain water and lead because the conductivity of sodium chloride is the highest. The electric field strength of lead is the highest followed by rain water and sodium chloride

Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Fault Prediction Based on Leakage Current in Contaminated Insulators Using Enhanced Time Series Forecasting Models

To improve the monitoring of the electrical power grid, it is necessary to evaluate the influence of contamination in relation to leakage current and its progression to a disruptive discharge. In this paper, insulators were tested in a saline chamber to simulate the increase of salt contamination on their surface. From the time series forecasting of the leakage current, it is possible to evaluate the development of the fault before a flashover occurs. In this paper, for a complete evaluation, the long short-term memory (LSTM), group method of data handling (GMDH), adaptive neuro-fuzzy inference system (ANFIS), bootstrap aggregation (bagging), sequential learning (boosting), random subspace, and stacked generalization (stacking) ensemble learning models are analyzed. From the results of the best structure of the models, the hyperparameters are evaluated and the wavelet transform is used to obtain an enhanced model. The contribution of this paper is related to the improvement of well-established models using the wavelet transform, thus obtaining hybrid models that can be used for several applications. The results showed that using the wavelet transform leads to an improvement in all the used models, especially the wavelet ANFIS model, which had a mean RMSE of 1.58 × 10−3, being the model that had the best result. Furthermore, the results for the standard deviation were 2.18 × 10−19, showing that the model is stable and robust for the application under study. Future work can be performed using other components of the distribution power grid susceptible to contamination because they are installed outdoors.N/

Prediction of polluted insulator based on leakage current resistance insertion performance of short and medium transmission line model

The main objective of the transmission lines is to deliver power from the generator to the customers, with less losses and without any interruptions. however, pollution sources are increasing around the world, which are affecting one of the most important components of a power line, namely, the high voltage outdoor insulators. the accumulation of pollution on the surface of the insulator can affect its physical properties and create leakage current resistance. under suitable conditions, this resistance will lead to leakage current on the surface of the insulator. in previous studies, leakage current measurement on the insulator surface was ignored because it is negligible. however, increasing pollution levels and the large number of transmission line insulators should take into account the effect of leakage current resistance in the transmission line model. in this thesis, an improved model is introduced to examine the effect of leakage current resistance on the parameters of the transmission line, the amount of additional active power losses, voltage drop and increased real power generation in power networks for both short and medium transmission lines. three levels of leakage resistance (high, medium, and low) that represent the three levels of pollution are incorporated into the transmission line model through a series of delta to star and star to delta conversion using a two-port network concept. then, by inserting the leakage current resistance, a simulation model was used to measure leakage current and voltage of the leakage current resistance. a simulation sensor is used to predict the level of pollution on the insulator and the location of highly polluted insulators using artificial neural network. this study was able to determine the changes in each parameter and the effects of these changes on the active power losses and voltage drop in three different systems. the application of the improved model have shown an increase in detection of power losses by 25.63% in high pollution conditions at the insulators in all short and medium transmission lines. thus, to compensate for these high losses, the system needs to increase real power generation by 0.61% when compared with during normal conditions. the prediction results by the simulation model for the 5- bus system clearly demonstrated that the overall correct classification rates for the predicted pollution levels were very high at 97.67% and 98.03%, for both short and medium models, respectively. meanwhile, the correct classification rate for the predicted locations of highly polluted insulators is 100% for both short and medium models. the results obtained in this study offer accurate information for polluted transmission line insulators, which could be used for maintenance and calculation of power loss for polluted insulators, in order to keep the power system in a reliable state

Study of surface discharge behaviour at the oil-pressboard interface

This thesis is concerned with the surface discharge behaviour at the oil-pressboard interface. For large transformers this is classified as a serious failure mode because it can lead to catastrophic failure under normal AC voltage operating conditions. To increase understanding on this failure mode, a surface discharge experiment at the oil-pressboard interface has been conducted on different moisture levels in pressboard by applying a long period of AC voltage stress. The processes in the surface discharge at the oil-pressboard interface until the appearance of a first full discharge have been recognised and correlated with the measured data. The results show that the different moisture levels within the pressboard play an important role on the partial discharge (PD) activity of certain processes. The decreasing trend in the PD data during the surface discharges cannot be treated as a reliable condition monitoring measure of health because it is the key indicator of white marks propagation toward the earth point. The characteristics of full discharge events have been analysed to develop knowledge for condition monitoring of surface discharge at the oil-pressboard interface. Full discharges are corona-like events in which their random occurrences are dominated by accumulated charges on the pressboard surface along the white marks rather than the polarity of applied AC voltage. A 2-D axial symmetry surface discharge model has also been developed using COMSOL Multiphysics, a finite element analysis (FEA) software package. The model considers the pressboard region near the interface (a transition region) as porous, whilst in the bulk region of pressboard as a perfect insulator. The model is developed using continuity equations and coupled with the Poisson’s equation to study the problem in terms of charge transport mechanisms and electric field distributions. The thermal conduction equation is included to study the thermal effects of surface discharge activity at the oil-pressboard interface. The behaviour of surface discharge is studied by validating the simulated surface discharge current pulse with the measured current. The simulation results show that a field dependent molecular ionisation mechanism plays an important role in the streamer propagation during the period of the rising front of the current pulse, whilst during the period of decaying tail of the current pulse, the contribution of an electron attachment process is dominant. The modelling results suggest that degradation marks (white and black marks) are due to high energy over long periods of partial discharge events that lead to thermal degradation at the oil-pressboard interface

Fabrication of durable self-healing superhydrophobic coating to improve the performance of high voltage insulators during winter conditions

With the emerging advancements in different fields of new materials, polymers, and technologies which have been revolutionary in industries, the demand for new generation of multi-functional materials with specific properties is highly growing. Superhydrophobic and self-healing materials are among these developments and have arisen as an unstoppable demand in the recent decades. In real world applications, coatings and surfaces are subjected to mechanical damages that are severe threat to the integrity of the structures. Once polymeric structures are damaged, there might be few limited methods available to sustain their functional lifetime. By the inspirations from mother nature and biological systems, the self-healing composite materials are designed to trigger a self-repair response without any or slight external human intervention. Herein, we aimed at designing a multifunctional superhydrophobic coating in order to increase the effective life-span of high-voltage insulators by preventing and/or delaying the possible arcing and flashover driven damages that originated from wettability issues and mechanical damages. Firstly, a telechelic silanol terminated polydimethylsiloxane (DMS-S12) and catalyst (Dibutyl tin dilaurate, DBTL) were encapsulated inside poly (melamine-urea-formaldehyde) shells separately via emulsion polymerization technique. The encapsulation of core materials, surface morphology and size distribution of microcapsules, and thermal stability of microcapsules were investigated. The synthesized microcapsules were obtained within a size range of 10-110 μm showing a spherical and uniform morphology, and thermal stability up to elevated temperatures. The microcapsules were incorporated inside a polydimethylsiloxane (PDMS) elastomer matrix, namely SILGARD 184, and the healing performance of the silicone composite was evaluated by monitoring a crack repair via scanning electron microscopy (SEM) and measuring the extent of recovery in mechanical properties via tensile and tear tests. The composites containing microcapsules depicted self-healing efficiencies of 67% and 55% calculated based on the recovered toughness and tearing energy of the healed samples. Secondly, a silicone-based superhydrophobic (SHP) coating was developed using spray coating method which was applicable to a variety of substrates including glass, porcelain, aluminum, and steel. The developed coating exhibited contact angle of 163° and contact angle hysteresis of 2.3° with excellent self-cleaning (in both dry and wet pollution scenarios) and icephobic (low ice adhesion and high delay in freezing time) properties. Robustness and durability which are the Achilles heel of superhydrophobic materials were assessed via a set of mechanical and chemical testing techniques in which the great non-wetting properties of the as-prepared coating was shown to be maintained even after various extreme treatments, i.e., waterjet impacting, immersing in pollutants and acid/base solutions for 24 h, tape peeling test, and sandpaper abrasion. Thirdly, the performance of superhydrophobic coating under electrical stress was evaluated employing a variety of methods including dielectric spectroscopy analyses, flashover voltage measurements tests, condensation, and inclined plane tests. The SHP coating represented lower dielectric permittivity and loss factor compared to a pristine sample within the frequency range of 10-4 – 103 Hz. Also, the leakage current results showed that the coating successfully reduced the leakage current on its surface in environments with high humidity. Moreover, the developed coating was able to increase flashover voltage in different conditions including dry, wet, and polluted states. Lastly, the obtained self-healing microcapsules were adapted for incorporation in thin layer surface coatings by some modifications in the process parameters. The SEM observations illustrated mean diameters of 18 and 16 μm for microcapsules. For the evaluation of self-healing ability, the scratched coatings were visually inspected using microscopy imaging. Electrochemical Impedance Spectroscopy (EIS) was employed to quantitatively investigate the self-healing function of the as-prepared coating. The self-healing efficiency and delamination index of the coating were calculated using the obtained data from EIS measurements (charge transfer resistance (Rct) and impedance (Z0.01 Hz)). The data showed self-healing efficiencies up to 96% compared to the blank superhydrophobic coating. The delamination index of the samples also confirmed the healing of the microcrack after 48 hours. Avec l’émergence dans plusieurs domaines de nouveaux types de matériaux, polymères et technologies qui ont révolutionné les infrastructures sociales et industriels, la demande pour des matériaux de nouvelle génération multifonctionnels à propriétés spécifiques enregistre une forte croissance. Notamment, les matériaux superhydrophobes et autoréparant ont connu une ascension fulgurante, au cours des dernières décennies. Dans des applications pour la vie quotidienne, les revêtements et les surfaces subissent de sévères contraintes mécaniques qui affectent l’intégrité des structures à long terme. Pourtant, il existe très peu de méthodes disponibles pour maintenir l’efficacité et leur durabilité lorsque les surfaces polymériques sont abimées. Ainsi, s’inspirant de mère nature et du potentiel auto-régénérassions des systèmes biologiques, des matériaux composites autoréparant ont été développé pour apporter une solution auto-réparatrice avec très peu voire aucune intervention humaine. Ici, la conception d’un revêtement superhydrophobe multifonctionnel capable d’augmenter la durée de vie effective des isolateurs à haute tension est au coeur de notre préoccupation. Ce dernier vise à prévenir voire retarder les éventuels dommages mécaniques causés par les arcs électriques et les contournements résultant de problèmes de mouillabilité et de ces dommages. Dans un premier temps, un polydiméthylsiloxane doté d’une terminaison en silanol téléchélique (DMS-S12) et un catalyseur (dilaurate de Dibutylétain, DBTL) ont été encapsulés séparément dans membrane de poly (mélamine-urée-formaldéhyde) via la technique de polymérisation en émulsion. L'encapsulation des matériaux du noyau ainsi que la morphologie de surface, la distribution de leur taille et la stabilité thermique des microcapsules ont été étudiées. Les microcapsules synthétisées présentaient un diamètre compris entre 10-110 μm avec une morphologie sphérique et uniforme, et une stabilité thermique jusqu'à des températures élevées. Celles ont été incorporées par la suite à l'intérieur d'une matrice élastomérique de polydiméthylsiloxane (PDMS), dénommée SILGARD 184 pour former le revêtement composite. Le potentiel de cicatrisation du composite de silicone ainsi obtenu a été évalué en surveillant une réparation de fissure par microscopie électronique à balayage (MEB) et en mesurant l'ampleur de la récupération des propriétés mécaniques par des essais de traction. Dans un second temps, le revêtement développé a été appliqué par pulvérisation sur une variété de substrats notamment le verre, la porcelaine, l'aluminum et l'acier. Le revêtement présent un angle de contact de 163° et une hystérésis d'angle de contact de 2.3° avec d'excellentes propriétés autonettoyantes (évalué en pollution sèche et humide) et glaciophobes (faible adhérence à la glace et retard élevé du temps de congélation). La robustesse et la durabilité représentent généralement le talon d'Achille des matériaux superhydrophobes. C’est pourquoi un ensemble des essais mécaniques et chimiques ont été effectués pour évaluer la robustesse du revêtement final vis à vis des conditions réels. Les résultats recueillis ont confirmé la stabilité des propriétés du revêtement développé soumis à conditions extrêmes. Troisièmement, la performance du revêtement superhydrophobe final (SHP) sous contrainte électrique a été évaluée à l'aide de diverses méthodes tels que la spectroscopie diélectrique, des tests de mesure de tension d'amorçage, de condensation et des tests de plan incliné. Le revêtement SHP offrait une permittivité diélectrique et un facteur de perte inférieurs à ceux d'un échantillon vierge dans la plage de fréquences est comprise entre 10-4 et 103 Hz. De plus, les résultats portant sur le courant de fuite ont montré que le revêtement réduisait avec succès le courant de fuite à sa surface dans des environnements à forte humidité. En plus, une augmentation de la tension de contournement dans différentes conditions qu’il s’agisse d’un état sec, humide ou pollué a été observée. Enfin, les microcapsules autoréparants obtenues ont été adaptées/ redimensionnées pour être incorporées dans des revêtements de surface de manière à obtenir une couche mince grâce à certaines modifications des paramètres du procédé. Les observations MEB ont révélé des diamètres moyens de 18 et 16 μm pour les microcapsules. Concernant l'évaluation de la capacité d'auto-guérissons, les revêtements ont été rayés et inspectés visuellement en utilisant l'imagerie par microscopie. La spectroscopie d'impédance électrochimique (EIS) a été également utilisée pour étudier quantitativement la fonction d'auto-guérissons du revêtement tel que préparé. L'efficacité d'auto-guérissons et l'indice de délaminage du revêtement ont été calculés à l'aide des données obtenues à partir des mesures EIS (résistance de transfert de charge (Rct) et impédance (Z0.01 Hz)). Les données ont montré des efficacités d'auto-guérissons allant jusqu'à 96% par rapport au revêtement superhydrophobe vierge. L'indice de délaminage des échantillons a également confirmé que la cicatrisation de la microfissure a lieu après 48 heures