Influence de la qualité de l’huile isolante sur le refroidissement des transformateurs de puissance

Les transformateurs sont des machines électriques statiques qui, introduits dans un circuit en courant alternatif, modifient la tension et le courant sans changer la fréquence. Ils sont utilisés dans chaque facette de nos maisons et entreprises. Ces équipements d’importance capitale, présentent des pertes d’énergie qui provoquent une élévation de température. En haute tension, cette élévation est limitée par l’emploi d’huiles ou de liquides, en refroidissement naturel (convection) ou forcé (circulation). Dans cet article, l’emphase est mise sur l’impact des produits colloïdaux (contaminants ou autre produits dissouts) sur la capacité de l’huile à refroidir les transformateurs de puissance. Des échantillons d’huiles ont été vieillis artificiellement en laboratoire et certaines propriétés de l’huile incluant la viscosité ont été mesurées à différentes durées du vieillissement. Les résultats obtenus montrent que les produits colloïdaux affectent la capacité de l’huile à dissiper la chaleur

Outdoor insulation and gas-insulated switchgears

Introduction With the growth of the world’s population and faster-developing industries, larger amounts of electric energy are needed [1–6]. To reduce Joule losses at longer distances, voltages delivered by generators are increased with step-up power transformers, and electric energy is transported at large voltages [7,8]. Consequently, many ultra/extra AC/DC high-voltage transmission projects have been commissioned or are under construction in many countries: Canada (735 kV), Venezuela (800 kV), China (1100 kV), Japan (1100 kV), and India (1200 kV) [9–18]. For the power to be delivered to end-users, transmission grids, including towers, conductors, insulators, as well as substations, are essential [19–22]. The main equipment in substations includes, but is not limited to: power transformers, circuit breakers, surge arrestors, relays, insulators, disconnector switches, busbars, capacitor banks, batteries, wave trapper, switchyard, as well as protection, control, and metering instruments, etc. When the equipment is installed outside, it is refereed as an “outdoor substation” and an “indoor substation” when set inside a building. One of the main advantages of an indoor substation over an outdoor substation is the independence from meteorological impacts [23–25]. Nowadays, indoor substations are commonly gas-insulated substations (GIS), as they require a much smaller footprint [23]

Towards online ageing detection in transformer oil: a review

Transformers play an essential role in power networks, ensuring that generated power gets to consumers at the safest voltage level. However, they are prone to insulation failure from ageing, which has fatal and economic consequences if left undetected or unattended. Traditional detection methods are based on scheduled maintenance practices that often involve taking samples from in situ transformers and analysing them in laboratories using several techniques. This conventional method exposes the engineer performing the test to hazards, requires specialised training, and does not guarantee reliable results because samples can be contaminated during collection and transportation. This paper reviews the transformer oil types and some traditional ageing detection methods, including breakdown voltage (BDV), spectroscopy, dissolved gas analysis, total acid number, interfacial tension, and corresponding regulating standards. In addition, a review of sensors, technologies to improve the reliability of online ageing detection, and related online transformer ageing systems is covered in this work. A non-destructive online ageing detection method for in situ transformer oil is a better alternative to the traditional offline detection method. Moreover, when combined with the Internet of Things (IoT) and artificial intelligence, a prescriptive maintenance solution emerges, offering more advantages and robustness than offline preventive maintenance approaches

High-Voltage engineering and applications in our modern society

Electrical energy is polymorphic, with voltage levels varying between a few volts to MVs and frequencies from a few Hz to MHz. This variability offers flexibility of use. For engineering applications, the choices of electrical parameters are dictated by technical and/or economic criteria. For example: - In aviation, frequencies from 400 Hz to a few kHz are used. - Energies produced at power stations are increased to kV levels with the step-up transformers to reduce Joule losses in long-distance transportations [1,2]. Consequently, many AC–DC transmission line projects up to 1200 kV have been constructed or are under way in many countries [3–15]. The application of high voltage in electrical power transmission is the most common, but electrical engineers also use this know-how in many other fields (e.g., [15–21]). Table 1 lists some of the main applications

Review of streamer dynamics and surface charge accumulation on ice surfaces

This paper reviews the main contributions of the CIGELE research team to the dynamics of streamer discharges along ice surfaces. These investigations were mainly performed under lightning impulse voltage, in atmospheric air. High-speed streak photography techniques were used to observe the streamers propagating between a rod-plane configuration half-submerged in ice bulk. The dynamics of streamer were investigated as influenced by the voltage characteristics, gap configuration, freezing water conductivity, and surrounding temperature. In addition to ice surface, corona discharge was also studied at insulator surface and at the air gaps between the electrodes in order to assess the role played by ice surface on discharge inception and propagation processes. The paper is not restricted to previously published work but contains a substantial amount of new material with a view to closing some major gaps in the present state of ice surface flashover knowledge

Special Issue "Selected Papers from the 2018 IEEE International Conference on High Voltage Engineering (ICHVE 2018)"

Articles sélectionnés, ICHVE 2018, Conférence internationale, Ingénierie de haute tension, IEE

Security risk modeling in smart grid critical infrastructures in the era of big data and artificial intelligence

Smart grids (SG) emerged as a response to the need to modernize the electricity grid. The current security tools are almost perfect when it comes to identifying and preventing known attacks in the smart grid. Still, unfortunately, they do not quite meet the requirements of advanced cybersecurity. Adequate protection against cyber threats requires a whole set of processes and tools. Therefore, a more flexible mechanism is needed to examine data sets holistically and detect otherwise unknown threats. This is possible with big modern data analyses based on deep learning, machine learning, and artificial intelligence. Machine learning, which can rely on adaptive baseline behavior models, effectively detects new, unknown attacks. Combined known and unknown data sets based on predictive analytics and machine intelligence will decisively change the security landscape. This paper identifies the trends, problems, and challenges of cybersecurity in smart grid critical infrastructures in big data and artificial intelligence. We present an overview of the SG with its architectures and functionalities and confirm how technology has configured the modern electricity grid. A qualitative risk assessment method is presented. The most significant contributions to the reliability, safety, and efficiency of the electrical network are described. We expose levels while proposing suitable security countermeasures. Finally, the smart grid’s cybersecurity risk assessment methods for supervisory control and data acquisition are presented

Impact of free radicals on the electrostatic charging tendency of transformer oils

In this contribution, the influence of free radical concentration on the electrostatic charging tendency (ECT) of aged mineral oils is reported. A free radical reagent, 2,2 diphenyl-1-picrylhydrazyl, is used to assess the relative concentration of free radicals. Prior to the ECT measurement, the oil samples were subjected to various stresses (corona discharges, multiple arcs or local overheating). Different ASTM standards were considered to assess the physicochemical properties before and after stress applications. It is found that free radicals affect the ECT. The theoretical premises that, free radicals may contribute to the ECT, are experimentally confirmed under laboratory conditions. The reason why this information is important is that ECT can significantly affect partial discharge inception in in-service transformers

Development of a new bi-arc dynamic numerical model for modeling AC flashover processes of EHV ice-covered insulators

This paper presents the development of a new bi-arc dynamic numerical model for predicting AC critical flashover voltage (FOV) of ice-covered extra-high voltage (EHV) insulators. The proposed model is based on a generic calculation algorithm coupled with commercial finite element method software designed to solve the Obenaus/Rizk model. The proposed model allows one to implement the Nottingham and Mayr approaches and compare the results obtained as a function of the arcing distance, the freezing water conductivity, and the initial arc length. The validation of the model demonstrated high accuracy in predicting the FOV of ice-covered post-type insulators and its capability to simulate the interaction of the two partial arcs during the flashover process. In particular, the results showed that the Nottingham approach is sensibly more accurate than the Mayr one, especially in simulating the dynamic behavior of the partial arcs during the flashover process. Based on the encouraging results obtained, a multi-arc calculation algorithm was proposed using the bi-arc dynamic numerical model as a basis. The basic idea, which consists in dividing the multi-arc model in several bi-arc modules, was not implemented and validated but will serve as a promising concept for future work

Numerical modelling of ice-covered insulator flashover : the influence of arc velocity and arc propagation criteria

This paper investigates the influence of arc velocity and propagation criteria on the parameters of a dynamic numerical mono-arc model used to predict flashover voltage of ice-covered insulators. For that purpose, a generic algorithm has been developed which, coupled with a Finite Element commercial software, permits us to solve the mono-arc Obenaus equation. The versatility of the proposed algorithm allows to implement three different arc propagation criteria and five different arc velocity criteria, as well as to compute the corresponding flashover voltage, arc velocity and leakage current. Moreover, this algorithm permits to propose a new arc velocity criterion based on numerical calculation instead of analytical formulation as proposed in literature