Developing a smart monitoring system for leakage currents from insulators on wooden poles

In Australia and many other countries, power distribution lines are carried on wooden poles. These lines suspended on insulators, which are fixed to wooden poles, pass cities as well as bushlands. Under different weather conditions, insulators become contaminated, and in particular, with damp weather, these insulators lose their ability to provide a perfect insulation between the high voltage conductor and the ground (through high impedance objects such as wood). A leakage current, small in magnitude, starts flowing from the high voltage conductor to the ground across the polluted insulator and through the wooden pole. If this phenomenon continues over some time, the currents start heating the wood where there is an abundance of wood-to-metal contact. At a certain stage, it will start smoking and this may lead to a pole fire. The obvious consequences of this are the loss of power to customers, public safety hazards and potential disasters such as bushfires. This thesis aims at determining which measure or combination of measures of leakage current are best suited for creating a ‘Leakage Current Health Index’ (LCHI) that can be later used to provide a power system operator with health status for a feeder or system, indicating how urgent a response is needed. To achieve this goal, the impedance characteristics of wooden poles altering the leakage current from insulators are investigated to better understand the role of wood in leakage current signatures. The effective impedance of wood used for poles in Victoria, Australia is established for the first time. Examining the impedance properties of typical Copper Chromium Arsenate (CCA) impregnated wood for 66 kV distribution poles shows dangerous conductance properties of wood at this voltage, providing an explanation for these poles catching fire at triple the rate of 22 kV distribution poles. After a systematic investigation of wood used for poles, a typical impedance characteristic is established for a weathered CCA impregnated wooden pole operating at 22 kV under both dry and wet weather conditions. Next, the leakage current from a single high voltage insulator is examined for various contamination levels and under different weather conditions. A new nonlinearity measure is established which utilises the Pearson correlation coefficient to measure the degree of leakage current nonlinearity and to build leakage current profiles of a single insulator under different conditions prior to flashover. Several fractal dimensions are also considered for the first time to measure characteristics of the leakage current profile of a single insulator. These measures are able to quantitatively differentiate between various levels of insulator contamination and different weather conditions, showing an enhanced level of nonlinear activity in the stage prior to insulator flashover. After developing an understanding of a single insulator, systematic modelling is used to build measure profiles of leakage currents for a simple power line, a lossless power line and a lossy power line. Finally, power utility zone substation data for a pole top fire are examined to verify the validity of the profiles observed utilising the measuring techniques determined suitable for establishing a LCHI

Two-arc dynamic modeling of AC and DC flashovers of EHV post station insulators covered with ice based on laboratory experiments

L'accumulation de glace et de neige sur les isolateurs a été reconnue comme l'un facteur de risque les plus importants dans la fiabilité des lignes de transmission aériennes et des postes électriques. La glace accumulée sur les isolateurs peut amorcer des décharges électriques le long des zones exempts de glace, souvent appelés espaces d'air. En présence d'un film d'eau très conducteur à la surface de la glace, sous une tension appliquée suffisamment élevée, des décharges partielles peuvent être initiées et se développer en arcs partiels. Sous certaines conditions, ces arcs partiels peuvent entraîner le contournement total de la chaîne d'isolateurs et provoquer des pannes d'électricité. L'objectif général de cette recherche est d'étudier le phénomène du contournement électrique des isolateurs de poste extra-haute tension (THT) recouverts de glace. Ainsi, des modèles dynamiques à deux arc, basées sur des modèles mathématiques existants a été proposé pour prédire les paramètres du contournement en courant continu (CC) et alternatif (CA). Le modèle considère l'arc comme une impédance dépendant du temps, constituée d'une résistance en série avec une inductance. La couche de glace résiduelle est définie en termes de résistance équivalente, où la conductivité surfacique équivalente est calculée en tenant compte du film d'eau coulant à la surface de la glace. La présente contribution propose une nouvelle approche permettant de déterminer la conductivité surfacique équivalente. Cette approche est basée sur des concepts de mécanique des fluides incluant les équations de Navier-Stokes, ainsi que sur une série d'expériences menées pour quantifier le débit du film d'eau et la conductivité surfacique équivalente. De plus, les mécanismes à l'origine de l'amorçage des décharges et du développement de l'arc sur la surface de la glace accumulée sur les isolateurs ont été étudiés. Une attention particulière a été accordée à l'évaluation de l'effet de la conductivité volumique de la surface de la glace sur la vitesse de propagation de l'arc pour différentes conductivités de l'eau de congélation, en utilisant des techniques d'enregistrement par caméras vidéo à haute vitesse. Les modèles proposés ont été validés avec succès en laboratoire sur des isolateurs de poste - généralement utilisés dans Hydro-Québec 735 kV - sous tensions CA et CC. La tension de tenue maximale en CC et CA ont été déterminées expérimentalement basés sur la norme IEEE Std 1783. En outre, l'influence du nombre et la position des intervalles d'air sur le contournement des isolateurs recouverts de glace a été étudiée expérimentalement. Les résultats expérimentaux ont montré que la configuration des espaces d'air affecte significativement la tension de tenue maximale. Les principales caractéristiques de contournement, comprenant la tension minimale de contournement et le courant de fuite, prédits par le modèle dynamique à deux arc proposé, concordent à la variation des principaux paramètres, à savoir, la longueur de 'isolateur et la conductivité de l'eau de congélation. Enfin, pour interpréter la performance des isolateurs sous différentes positions des espaces d'air, les distributions de champ électrique et tension le long de l'isolateur recouvert de glace ont été simulés numériquement au cours de la période de fonte, en utilisant la méthode des éléments finis (MEF). Les résultats de simulations confirment que l'augmentation du nombre d'espace d'air améliore la tension de tenue maximale ainsi que l'uniformité de la distribution de tension le long des isolateurs de poste THT. Selon les résultats obtenus, l'utilisation des jupes d'appoint (booster sheds) et anneaux de garde pour améliorer les performances d'isolation des isolateurs de poste dans des conditions de givrage est recommandé. Cette recherche peut être considérée comme une base importante pour le développement de modèles multi-arc et un outil puissant pour la conception et le choix des isolateurs THT soumis à l'accumulation de glace. - Ice and snow accretion on insulators has been recognized as a significant risk factor in the reliability of overhead transmission lines and substations. Accumulated ice on insulators can initiate corona discharge along ice-free zones, often called air gaps. In the presence of a highly conductive water film on the surface of the ice, while applied voltage is sufficiently high, corona discharge activity may be initiated and developed into partial arcs. Under certain conditions, these partial arcs may result in complete flashover. The general objective of this research is to study the flashover phenomenon on icecovered extra-high-voltage (EHV) post insulators. Hence, a two-arc dynamic model based on the existing mathematical models was proposed to predict the parameters of AC and DC flashovers. The model considers the arc as time-dependent impedance constituted of a resistance in series with an inductance. The residual ice layer is defined in terms of an equivalent resistance, where the equivalent surface conductivity is calculated by taking into account the water film flowing along the ice surface. The present contribution proposes a novel approach to determine the equivalent surface conductivity, based on fluid mechanics and the Navier-Stokes equations, as well as on a series of experiments carried out to measure the water film flow rate and conductivity. Moreover, the mechanisms of discharge initiation and arc development on the surface of the ice accumulated on the insulators were studied. Special attention was paid to evaluate the effect of the volume conductivity of the ice surface on the arc propagation velocity for different freezing water conductivities, using high-speed video camera techniques. The proposed models were successfully validated in laboratory using station post insulators - typically used in Hydro-Quebec 735 kV substations - under AC and DC voltages. The maximum AC and DC withstand voltages were experimentally determined based on IEEE Std 1783. Furthermore, the influence of the number and position of air gaps on the flashover performance of ice-covered insulators was investigated experimentally. Experimental results revealed that the air gap configuration affects the maximum withstand voltage significantly. The main characteristics of flashover, including minimum flashover voltage and leakage current, derived from the proposed two-arc dynamic model, respond properly to the variation of major parameters, namely, insulator length and freezing water conductivity. Finally, in order to interpret the performance of insulators under different air gap positions, the voltage and electric field distributions along the ice-covered insulator were simulated numerically during the melting period, using the Finite Element Method (FEM). Simulations results confirm that increasing the number of air gaps improves the maximum withstand voltage and uniformity of voltage distribution of EHV post insulators. Based on the results, the use of booster sheds and grading rings to improve the insulating performance of post insulators under icing conditions is recommended. This research may be regarded as an important basis for the development of multi-arc models and a powerful tool for the design and selection of EHV insulators subjected to ice accretion

7th EEEIC International Workshop on Environment and Electrical Engineering : Wroclaw - Cottbus, 5 - 11. May 2008

The proposed solution meets the latest trends in world power engineering and has the lowest ecological costs amongst the accessible power engineering solutions. It is also in accordance with the Polish power engineering law, which takes into account the recommendations of the European Economic Commission, the Second Sulphur Protocol and the Framework Convention of the United Nations (concerning the changes of climate)

Integrated Micro Gas Chromatographs with High-Flow Knudsen Pumps.

Environmental gas sensing typically requires both sensitivity and specificity; target vapor species must not only be detected and quantified, but also differentiated from interferents. This mission can be accomplished by micro gas chromatographs (μGCs), which allow preconcentration of samples and subsequent separation of complex vapor mixtures into individual constituents by their specific retention times. This thesis focuses on the system-level design, fabrication, and integration of μGCs, with the ultimate goal of fully microfabricated systems that can be easily manufactured and distributed to end-users. This thesis also explores the optimization of a micro gas pump – a critical μGC component, and generally recognized as a challenge for microsystems. Three generations of integrated µGC systems have been designed, fabricated, and evaluated. The iGC1 system demonstrates the feasibility of a low-cost three-mask fabrication approach for a µGC including a Knudsen pump, a preconcentrator, a separation column and a microdischarge-based detector, which are integrated in a 4-cc stack. The iGC2 system demonstrates a valveless µGC architecture, in which a bi-directional Knudsen pump provides reversible gas flow for (multi-stage) preconcentrators, which is essential for quantitative analysis. The iGC3 system replaces the microdischarge-based detectors in iGC1 and iGC2 with complementary capacitive detectors, facilitating a purely electronic interface for the fluidics. Additionally, it is compatible with the use of room air as the carrier gas. The quantitative analysis of 19 chemicals with concentration levels of well below 100 ppb is demonstrated, showing the promise of automated, continuous monitoring of indoor air pollutants. The pumps used in the iGCx systems are Knudsen pumps that use thermal transpiration provided by nanoporous media and have no moving parts. This thesis also describes an exploratory effort in which lithographically fabricated channels in silicon substrates provide the thermal transpiration. The Si-micromachined Knudsen pumps demonstrate >200 sccm flow rate. To increase the output pressure head, these pumps are arrayed in series, using both a stacked configuration and a planar one. The results show that the pressure and flow characteristics can be tailored over a wide performance range, extending the possible applications beyond µGC systems.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113581/1/yutaoqin_1.pd

Fiber Bragg Grating Based Sensors and Systems

This book is a collection of papers that originated as a Special Issue, focused on some recent advances related to fiber Bragg grating-based sensors and systems. Conventionally, this book can be divided into three parts: intelligent systems, new types of sensors, and original interrogators. The intelligent systems presented include evaluation of strain transition properties between cast-in FBGs and cast aluminum during uniaxial straining, multi-point strain measurements on a containment vessel, damage detection methods based on long-gauge FBG for highway bridges, evaluation of a coupled sequential approach for rotorcraft landing simulation, wearable hand modules and real-time tracking algorithms for measuring finger joint angles of different hand sizes, and glaze icing detection of 110 kV composite insulators. New types of sensors are reflected in multi-addressed fiber Bragg structures for microwave–photonic sensor systems, its applications in load-sensing wheel hub bearings, and more complex influence in problems of generation of vortex optical beams based on chiral fiber-optic periodic structures. Original interrogators include research in optical designs with curved detectors for FBG interrogation monitors; demonstration of a filterless, multi-point, and temperature-independent FBG dynamical demodulator using pulse-width modulation; and dual wavelength differential detection of FBG sensors with a pulsed DFB laser

Dielectrics - Digest of literature, volume 28, 1964

Dielectric constants, dipole moments, relaxation times, conduction phenomena, insulating films, breakdown, materials, and applications of dielectrics - annotated bibliograph

Terahertz Technology and Its Applications

The Terahertz frequency range (0.1 – 10)THz has demonstrated to provide many opportunities in prominent research fields such as high-speed communications, biomedicine, sensing, and imaging. This spectral range, lying between electronics and photonics, has been historically known as “terahertz gap” because of the lack of experimental as well as fabrication technologies. However, many efforts are now being carried out worldwide in order improve technology working at this frequency range. This book represents a mechanism to highlight some of the work being done within this range of the electromagnetic spectrum. The topics covered include non-destructive testing, teraherz imaging and sensing, among others

Cumulative index to NASA Tech Briefs, 1986-1990, volumes 10-14

Tech Briefs are short announcements of new technology derived from the R&D activities of the National Aeronautics and Space Administration. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This cumulative index of Tech Briefs contains abstracts and four indexes (subject, personal author, originating center, and Tech Brief number) and covers the period 1986 to 1990. The abstract section is organized by the following subject categories: electronic components and circuits, electronic systems, physical sciences, materials, computer programs, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Applications and Experiences of Quality Control

The rich palette of topics set out in this book provides a sufficiently broad overview of the developments in the field of quality control. By providing detailed information on various aspects of quality control, this book can serve as a basis for starting interdisciplinary cooperation, which has increasingly become an integral part of scientific and applied research