Transformer condition assessment using Fuzzy C-means clustering techniques

This paper introduces a transformer fleet monitoring solution to help the end user to group transformer assets and react accordingly to monitored situations

Verification of insulation oil reclamation by turbidity and spetrophotometry measurements

Oil reclamation with Fuller’s earth is known to have an improved effect on conditioning aged oil. In this paper it is shown that aged oil reclamation effectiveness can be monitored with turbidity and spectrophotometry measurements. These low cost testing techniques offer a useful tool to quantify the effect of Fuller’s earth. Experimental investigations performed in laboratory conditions have shown that the quality of properly reclaimed aged oil can compete with that of new oils. Thus, in addition to extending the life cycle of this non-renewable resource, on-line reclamation of liquid might also prevent the premature ageing of paper insulation. Studying the stability of reclaimed service aged oil samples emphasized the important role played by Fuller’s Earth absorption capability

Contribution à l'étude des phénomènes de préclaquage dans les diélectriques liquides -Modèles de génération et de propagation des streamers,

This work deals with the pre-breakdown and breakdown phenomena in the liquid dielectrics. It is shown that the initiation of streamers, in a point-plane electrode arrangement, is preceded by the generation of a gaseous phase (bubble) at the point electrode. This bubble results of a current pulse injection into the liquid when the applied voltage reaches a threshold value Us. This latter increases quasi-linearly with the pressure. The addition of a certain concentration of an electronic scavenger compound increases Us ; this indicates that the electronic processes are also present. The analysis of the bubble dynamics shows that two types of deformation of the liquid-bubble interface can occur: (i) an expansion or an implosion and (ii) alternative movements of expansion and/or implosion. According to the disturbance mode of the interface, different types of streamers can be initiated. The dielectric strength of liquid increases when adding a given optimal concentration of electronic scavenger compounds (Iodobenzene or carbon tetrachloride) and/or increasing the pressure. Therefore, while acting on the initiation voltage of streamers, one can improve the dielectric strength of liquid even though the streamer velocity is increased. By increasing the pressure, one can also increase dielectric strength of a liquid. A modeling of streamers by an equivalent electrical network enables to determine the structure of streamers as well as their physical characteristics: currents, electrical charges, power and energy injected, electric fields and potentials at their heads, velocity and mobility of charge carriers within the streamer, local viscosity and temperature. Keywords: Dielectric liquids, pre-breakdown and breakdown, bubble dynamics, streamers, initiation and propagation, dielectric strength, additives and pressure, modeling.Ce travail est dédié aux phénomènes de préclaquage et de claquage dans les diélectriques liquides. Il est montré que dans un système d'électrodes pointe - plan, la génération des streamers est précédée par la formation d'une phase gazeuse (bulle) au voisinage de la pointe, résultant de l'injection d'une impulsion de courant dès que la tension appliquée atteint ou dépasse une certaine valeur seuil Us. Us augmente quasi-linéairement avec la pression. L'addition d'une certaine concentration de composés capteurs d'électrons augmente Us, preuve que les mécanismes électroniques sont également présents. L'analyse de la dynamique de la bulle montre que deux types de déformation de la surface de la bulle sont possibles: (i) une expansion ou une implosion et (ii) des mouvements alternatifs d'expansion et/ou implosion. Selon les modes de perturbation de l'interface, différents types de streamers peuvent prendre naissance. D'autre part, la tension de claquage d'un diélectrique liquide augmente en présence d'une concentration optimale donnée d'additifs capteurs d'électrons (Iodobenzène ou tétrachlorure de carbone). Par conséquent, en agissant sur la tension de génération des streamers, on peut améliorer la tenue diélectrique du liquide même si la vitesse des streamers est augmentée. En augmentant la pression, on peut aussi relever la tenue diélectrique d'un liquide. Une modélisation des streamers par des circuits électriques équivalents et leur résolution par le calcul de réseaux a permis de déterminer la structure des streamers ainsi que leurs paramètres caractéristiques : courants, charges, puissances et énergies injectés, champs électriques et différences de potentiel à leurs têtes, vitesse et mobilité des porteurs de charge dans le streamer, viscosité et température locales

Bubble dynamics and transition into streamers in liquid dielectrics under a high divergent electric field

International audienceThe paper deals with the dynamics of a bubble initiated in the vicinity of a sharp electrode in a liquid dielectric gap submitted to an electric field, and to the conditions leading to the generation of a streamer at the bubble-liquid interface. By taking into account the different stresses acting at any point of the surface of the bubble, we establish a mathematical expression describing the shape of the bubble and allowing us to analyse its deformation and instability. The frequency of the disturbances at the interface is studied and the zone at which the local electric field is the highest is determined. It is shown that depending on this frequency and therefore on the value of the local electric field, different streamer patterns can be generated. Some examples of the topology of the disturbed interface are given and discussed

Modelling of multi-channel streamers propagation in liquid dielectrics using the computation electrical network

International audienceThis work is devoted to the modelling of branching streamers, propagating in liquid dielectrics using an equivalent electrical network, physical laws and energetic considerations. This model enables the prediction of the characteristics of the streamer such as the current, the electrical charge, the energy and the power injected in the liquid medium, the local electric field, the streamer pattern and its velocity. The shape and amplitude of the different characteristics so simulated are in quite good accordance with those reported in the literature. It appears from our modelling that the shape and the propagation mode of the streamer depend not only on the test conditions but also on the local electric field. The values of the mobility of charge carriers within the streamer channels, the local viscosity and temperature deduced from this model indicate that both electronic and gaseous mechanisms are implicated in the streamer development

Non-Thermal Plasmas for NOx Treatment

International audienceThis work is devoted to the determination of corona ignition threshold for non-thermal plasma generation and to the optimization of various kinds of plasma reactor geometries for exhaust gas treatment applications. The tested plasma reactor geometries were cylindrical. Some reactors have dielectric barrier made of glass or quartz in order to observe the discharges. First, the distributions of electric field and energy in reactors have been simulated. Then, current and voltage waveforms have been measured to check the discharge appearance. Geometrical singularities have been detected by both luminescence and current measurements to avoid unwanted current distortions. The experimental analyze shows the evolution of resistive and reactive components of current associated to corona discharges when increasing the voltage

Characterization of the operating periods of a power transformer by clustering the dissolved gas data

International audienceThis paper presents an analysis of the different operating periods of an in-service oil immersed power transformer through dissolved gas concentrations. The unsupervised classification by k-means method allows regrouping the periods of operation into classes using the Euclidean distance as a criterion of similarity. The analyzed data describes the evolution of gas concentrations as a function of time. The classes obtained are characterized by the production activities of the different gases, various operating constraints and the incipient failures. These periods also highlight the maintenance actions carried out on the insulating oil

Power transformer condition monitoring by 2FAL content and CO2/CO ratio – A fuzzy logic approac

The condition of the solid insulation paper within transformers can be directly determined from the degree of polymerization (DP) measured from samples. Since this is difficult for in service units, many studies have been performed in regard with indirectly measuring the degradation of paper insulation by chemical markers for several decades. The 2-FAL concentration is being used decades ago. In this contribution, condition monitoring history and experience with transformer fleets are reported for a service aging of 75 years. 37 oil-filled transformers (146.7 kV to 157 kV) of a Canadian utility were periodically monitored. As part of the maintenance of the apparatus, the analysis of the furanic compounds is carried out. These are obtained by high performance liquid chromatography in a laboratory, with a regularity that varies according to the age of the transformer. This article deals with a transformer aging evaluation tool built from fuzzy logic. A fuzzy inference system is implemented by taking as input the values of 2-FAL and CO 2 /CO ratio. The tool helps directly providing the paper condition

Parameters Affecting the Formation of Corrosive Suphide Deposition on Copper Conductors

International audienc

Effect of electrical discharge on oil decaying process

International audienceSince the electrical stress is unavoidable in power transformers, the ability of oil to resist decomposition under electrical stress is of paramount importance for the safety of these important devices. Electrical stress together with heat and moisture, in the presence of oxygen, oxidises the oil producing free radicals, acids and sludge that are deleterious to the transformer. In this paper, the effect of electrical discharges on oil properties is reported. The results indicate that the quality of oil is considerably affected, with increasing voltage stress. Comparing oil properties before and after voltage application allow assessing the outcome of random secondary chemical reactions between large oil born free radicals