This study details the fabrication of an icephobic coating for steel produced using a silicone–ep... more This study details the fabrication of an icephobic coating for steel produced using a silicone–epoxy hybrid resin; the coating has good mechanical properties and weathering resistance for outdoor applications. Silicone–epoxy hybrid resins and amino‐functional silane‐curing agents were selected for investigation and applied to steel samples. Wettability, ice adhesion strength, and the mechanical and weathering resistance properties of the developed coatings were assessed using a drop‐shape analyzer, Fourier transform infrared, X‐ray photoelectron spectroscopy, as well as push‐off, tensile, and QUV tests. The possible correlation between ice adhesion strength and Young modulus was also investigated. The best‐performing matrix in terms of mechanical properties and weathering resistance had its surface energy characteristics altered—via two fluorinated silicone additives at various concentrations—to lower ice adhesion strength. For the steel substrates, the optimized additive‐altered su...
Ce travail presente un modele de decharge autonome permettant de predire le comportement d'un... more Ce travail presente un modele de decharge autonome permettant de predire le comportement d'un intervalle d'air soumis a une tension donnee (bi exponentielle pure ou oscillante). Ce modele est base sur un schema electrique equivalent, ses parametres variant avec le temps en fonction des caracteristiques du canal et de la geometrie de la decharge. La propagation du leader est basee sur un critere lie au calcul du champ a sa tete et ou le caractere aleatoire du trajet de la decharge est pris en compte. Le modele permet de determiner l'evolution des courants (leader et arc en retour), la charge correspondante, le gradient de potentiel dans le canal, une trajectoire plausible de la decharge, sa vitesse instantanee, l'evolution temporelle de son canal thermique, la puissance et l'energie injectee dans l'intervalle, l'instant et la tension d'amorcage. Aussi, pour une configuration donnee, ce modele constitue un outil pour la determination de la tension Us, (...
Smart Cities are making massive use of information and communication technologies, which are lead... more Smart Cities are making massive use of information and communication technologies, which are leading to significant digitization. However, the rate at which technology is currently being implemented is on the increase. Modern cities play a leading role in sustainable strategic development. They have a central position in developing and applying advanced technologies to support environmental sustainability in the face of the escalating urbanization trend. Smart grid specifics are finally starting to emerge from the marketing haze. In a smart grid, utilities manage their electrical supply and productivity cost-effectively, and energy customers benefit from a more efficient power system. This article focuses on the main strategies of the resource efficiency management associated with smart grid and sustainable cities.
The detection of On-Load Tap-Changer (OLTC) faults at an early stage plays a significant role in ... more The detection of On-Load Tap-Changer (OLTC) faults at an early stage plays a significant role in the maintenance of power transformers, which is the most strategic component of the power network substations. Among the OLTC fault detection methods, vibro-acoustic signal analysis is known as a performant approach with the ability to detect many faults of different types. Extracting the characteristic features from the measured vibro-acoustic signal envelopes is a promising approach to precisely diagnose OLTC faults. The present research work is focused on developing a methodology to detect, locate, and track changes in on-line monitored vibro-acoustic signal envelopes based on the main peaks extraction and Euclidean distance analysis. OLTC monitoring systems have been installed on power transformers in services which allowed the recording of a rich dataset of vibro-acoustic signal envelopes in real time. The proposed approach was applied on six different datasets and a detailed analys...
2015 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), 2015
The main objective of this contribution is to present a dynamic two-arc model to study the behavi... more The main objective of this contribution is to present a dynamic two-arc model to study the behavior of DC arcs on ice-covered post insulators. This model provides an appropriate tool to determine minimum flashover voltage (VMF) which is a determining factor in the selection of insulators under icing conditions. The proposed model takes into account the environmental pollution level, insulator geometry and, most importantly, applied voltage polarities. The model is validated against laboratory data consisting of flashover tests on a typical 735-kV ice-covered post insulator under DC voltage. The experimental results have good agreement with those computed by the proposed model. This model could be regarded as an important basis for the development of multi-arc models, not to mention being a powerful tool for the design and selection of EHV insulators subjected to ice accretion.
Le cout des bornes de traversee est relativement insignifiant, compare a celui des equipements de... more Le cout des bornes de traversee est relativement insignifiant, compare a celui des equipements de puissance pour lesquels elles permettent au courant de traverser la cuve metallique des appareils maintenue a la masse. Cependant, ces bornes sont tres importantes car leur defaillance peut entrainer la destruction totale de l'appareil. Par consequent, la qualite de leur isolation doit etre aussi excellente que possible. Dans ce travail, des techniques spectroscopiques dans les domaines temporel et frequentiel sont utilisees pour le suivi des differentes etapes de fabrication d'une borne de traversee. Les resultats obtenus montrent que l'application de ces methodes a la surveillance de l'isolation des equipements de puissance durant la fabrication est extremement utile ; les mesures effectuees fournissent des informations sur la qualite de cette isolation. Les defauts de fabrication etant des contraintes fortes que l'on se doit d'apprehender systematiquement lors...
Despite major progress in the design of power transformers, the Achilles’ heel remains the insula... more Despite major progress in the design of power transformers, the Achilles’ heel remains the insulation system, which is affected by various parameters including moisture, heat, and vibrations. These important machines require extreme reliability to guarantee electricity distribution to end users. In this contribution, a fiber optic sensor (FOS), consisting of a Fabry–Perot cavity made up of two identical fiber Bragg gratings (FBGs), is proposed, to monitor the temperature and vibration of power transformer windings. A phase shifted gratings recoated sensor, with multilayers of polyimide films, is used to monitor the moisture content in oil. The feasibility is investigated using an experimental laboratory transformer model, especially fabricated for this application. The moisture contents are well correlated with those measured by a Karl Fisher titrator, while the values of temperature compare well with those recorded from thermocouples. It is also shown that the sensors can be used t...
Frequency response analysis (FRA) is being employed worldwide as one of the main methods for the ... more Frequency response analysis (FRA) is being employed worldwide as one of the main methods for the internal condition assessment of transformers due to its capability of detecting mechanical changes. Nonetheless, the objective interpretation of FRA measurements is still a challenge for the industry. This is mainly attributable to the lack of complete data from the same or similar units. A large database of FRA measurements can contribute to improving classification algorithms and lead to a more objective interpretation. Due to their destructive nature, mechanical deformations cannot be performed on real transformers to collect data from different scenarios. The use of simulation and laboratory transformer models is necessary. This research contribution is based on a new method using Finite Element Method simulation and a lumped element circuit to obtain FRA traces from a laboratory model at healthy and faulty states, along with an optimization method to improve capacitive parameters f...
The service of mineral insulating oils for power transformer insulation and cooling aspects canno... more The service of mineral insulating oils for power transformer insulation and cooling aspects cannot be disavowed. However, the continued use of mineral oils is questionable due to environmental unfriendliness and the divestment from fossil fuels. This has provoked the quest for green alternative insulating liquids for high-voltage insulation. Natural esters are among the remaining alternatives that are renewable and environmentally friendly. Regardless of their environmental and technical merits, natural esters have some limitations that are slowing down their total acceptance by transformer owners and utilities. Critical limitations and concerns include esters’ pour point, viscosity, oxidative stability, and ionization resistance. In this work, the state of the art of “natural esters for transformers” is explored with the aim of potential improvements. The sections of the article are geared towards technical viewpoints on improving the overall workability and serviceability of natur...
The degradation of the insulation system in liquid-filled power transformers is a serious concern... more The degradation of the insulation system in liquid-filled power transformers is a serious concern for electric power utilities. The insulation system’s ageing is accelerated by moisture, acids, oxidation products, and other decay particles (soluble and colloidal). The presence of these ageing by-products is detrimental to the insulation system and may further lead to premature ageing and serious consequences. The ageing mechanisms of oil-paper insulation are complex, highly interrelated, and strongly temperature-dependent. The operating temperature of the transformer insulating system has a direct relationship with the loading profile. The major aspect that is witnessed with the fluctuating temperatures is moisture migration and subsequent bubble evolution. In other words, gas bubbles evolve from the release of water vapor from the cellulosic insulation wrapped around the transformer windings. The models presented in the existing standards, such as the IEC Std. 60076-7:2018 and the ...
Insulation cellulose paper is a basic measure for a power transformer’s remaining useful life, an... more Insulation cellulose paper is a basic measure for a power transformer’s remaining useful life, and its advantageous low cost, electrical, and mechanical properties have made it an extensive insulation system when impregnated in a dielectric liquid. Cellulose paper deteriorates as a result of ageing due to some chemical reactions like pyrolysis (heat), hydrolysis (moisture), and oxidation (oxygen) that affects its degree of polymerization. The condition analysis of cellulose paper has been a major concern since the collection of paper samples from an operational power transformer is almost impossible. However, some chemicals generated during cellulose paper deterioration, which were dissolved in dielectric liquid, have been used alternatively for this purpose as they show a direct correlation with the paper’s degree of polymerization. Furthermore, online and non-destructive measurement of the degree of polymerization by optical sensors has been proposed recently but is yet to be avai...
In the last decades, a large focus is being placed on the sustainability and safety of the power ... more In the last decades, a large focus is being placed on the sustainability and safety of the power transformer spectrum. Ester liquids, which have interesting properties such as high fire point and biodegradability, are gaining needed attraction. Since in-service condition, thermal aging deteriorates the physicochemical and electrical properties of liquid dielectrics, it is important to study their long-term behavior. In this contribution, the pre-breakdown and breakdown behavior of ester fluids (synthetic and natural) under AC stress are investigated. Important characteristics, such as partial discharge pre-inception voltage, partial discharge inception voltage, breakdown voltage, average streamer velocity, and inception electric field, were assessed. The influence of the radius of curvature (of high voltage needle electrode) as well as the thermal degradation of typical ester liquids are also discussed. Mineral oil was also included in the tests loop as a benchmark for comparative p...
IEEE Transactions on Dielectrics and Electrical Insulation, 2021
Power transformers represent one of the most abundant and expensive components in the electric po... more Power transformers represent one of the most abundant and expensive components in the electric power industry. Dissolved gas analysis (DGA) of transformer is the most widely accepted diagnostic tool across the globe to understand insulation incipient failures. Nevertheless, DGA fault gas interpretation is a remarkable challenge for transformer owners and utility engineers. Several computational techniques have been adopted for DGA fault classification along with offline methods. However, limited data availability, high ambiguity in DGA interpretation, suitability, and model accuracy are critical challenges in the DGA fault classification using computational techniques. In this work, highly diverse and large DGA data samples of in-service transformer fleets from five different utilities have been used to develop an efficient fault classification methodology. A total of 4580 DGA samples and IEC TC 10 database are used for training and testing, respectively, for various machine learning algorithms. Discussions on performance indicators and evaluation of several algorithms to verify the most suitable class algorithms are also the focus of this work. Furthermore, a best-performing model is identified based on various performance indicators. The hyperparameters of the best model are further tuned to achieve a most precise fault classification. It is inferred that non-parametric methods and non-linear SVM are best suitable for transformer DGA fault classification. Importantly, the rankings in the present study suggest that transformer DGA fault prediction is better with ensemble learning methods.
With the growth of the world’s population and faster-developing industries, larger amounts of ele... more With the growth of the world’s population and faster-developing industries, larger amounts of electric energy are needed [...]
Electrical energy is polymorphic, with voltage levels varying between a few volts to MVs and freq... more Electrical energy is polymorphic, with voltage levels varying between a few volts to MVs and frequencies from a few Hz to MHz [...]
This study details the fabrication of an icephobic coating for steel produced using a silicone–ep... more This study details the fabrication of an icephobic coating for steel produced using a silicone–epoxy hybrid resin; the coating has good mechanical properties and weathering resistance for outdoor applications. Silicone–epoxy hybrid resins and amino‐functional silane‐curing agents were selected for investigation and applied to steel samples. Wettability, ice adhesion strength, and the mechanical and weathering resistance properties of the developed coatings were assessed using a drop‐shape analyzer, Fourier transform infrared, X‐ray photoelectron spectroscopy, as well as push‐off, tensile, and QUV tests. The possible correlation between ice adhesion strength and Young modulus was also investigated. The best‐performing matrix in terms of mechanical properties and weathering resistance had its surface energy characteristics altered—via two fluorinated silicone additives at various concentrations—to lower ice adhesion strength. For the steel substrates, the optimized additive‐altered su...
Ce travail presente un modele de decharge autonome permettant de predire le comportement d'un... more Ce travail presente un modele de decharge autonome permettant de predire le comportement d'un intervalle d'air soumis a une tension donnee (bi exponentielle pure ou oscillante). Ce modele est base sur un schema electrique equivalent, ses parametres variant avec le temps en fonction des caracteristiques du canal et de la geometrie de la decharge. La propagation du leader est basee sur un critere lie au calcul du champ a sa tete et ou le caractere aleatoire du trajet de la decharge est pris en compte. Le modele permet de determiner l'evolution des courants (leader et arc en retour), la charge correspondante, le gradient de potentiel dans le canal, une trajectoire plausible de la decharge, sa vitesse instantanee, l'evolution temporelle de son canal thermique, la puissance et l'energie injectee dans l'intervalle, l'instant et la tension d'amorcage. Aussi, pour une configuration donnee, ce modele constitue un outil pour la determination de la tension Us, (...
Smart Cities are making massive use of information and communication technologies, which are lead... more Smart Cities are making massive use of information and communication technologies, which are leading to significant digitization. However, the rate at which technology is currently being implemented is on the increase. Modern cities play a leading role in sustainable strategic development. They have a central position in developing and applying advanced technologies to support environmental sustainability in the face of the escalating urbanization trend. Smart grid specifics are finally starting to emerge from the marketing haze. In a smart grid, utilities manage their electrical supply and productivity cost-effectively, and energy customers benefit from a more efficient power system. This article focuses on the main strategies of the resource efficiency management associated with smart grid and sustainable cities.
The detection of On-Load Tap-Changer (OLTC) faults at an early stage plays a significant role in ... more The detection of On-Load Tap-Changer (OLTC) faults at an early stage plays a significant role in the maintenance of power transformers, which is the most strategic component of the power network substations. Among the OLTC fault detection methods, vibro-acoustic signal analysis is known as a performant approach with the ability to detect many faults of different types. Extracting the characteristic features from the measured vibro-acoustic signal envelopes is a promising approach to precisely diagnose OLTC faults. The present research work is focused on developing a methodology to detect, locate, and track changes in on-line monitored vibro-acoustic signal envelopes based on the main peaks extraction and Euclidean distance analysis. OLTC monitoring systems have been installed on power transformers in services which allowed the recording of a rich dataset of vibro-acoustic signal envelopes in real time. The proposed approach was applied on six different datasets and a detailed analys...
2015 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), 2015
The main objective of this contribution is to present a dynamic two-arc model to study the behavi... more The main objective of this contribution is to present a dynamic two-arc model to study the behavior of DC arcs on ice-covered post insulators. This model provides an appropriate tool to determine minimum flashover voltage (VMF) which is a determining factor in the selection of insulators under icing conditions. The proposed model takes into account the environmental pollution level, insulator geometry and, most importantly, applied voltage polarities. The model is validated against laboratory data consisting of flashover tests on a typical 735-kV ice-covered post insulator under DC voltage. The experimental results have good agreement with those computed by the proposed model. This model could be regarded as an important basis for the development of multi-arc models, not to mention being a powerful tool for the design and selection of EHV insulators subjected to ice accretion.
Le cout des bornes de traversee est relativement insignifiant, compare a celui des equipements de... more Le cout des bornes de traversee est relativement insignifiant, compare a celui des equipements de puissance pour lesquels elles permettent au courant de traverser la cuve metallique des appareils maintenue a la masse. Cependant, ces bornes sont tres importantes car leur defaillance peut entrainer la destruction totale de l'appareil. Par consequent, la qualite de leur isolation doit etre aussi excellente que possible. Dans ce travail, des techniques spectroscopiques dans les domaines temporel et frequentiel sont utilisees pour le suivi des differentes etapes de fabrication d'une borne de traversee. Les resultats obtenus montrent que l'application de ces methodes a la surveillance de l'isolation des equipements de puissance durant la fabrication est extremement utile ; les mesures effectuees fournissent des informations sur la qualite de cette isolation. Les defauts de fabrication etant des contraintes fortes que l'on se doit d'apprehender systematiquement lors...
Despite major progress in the design of power transformers, the Achilles’ heel remains the insula... more Despite major progress in the design of power transformers, the Achilles’ heel remains the insulation system, which is affected by various parameters including moisture, heat, and vibrations. These important machines require extreme reliability to guarantee electricity distribution to end users. In this contribution, a fiber optic sensor (FOS), consisting of a Fabry–Perot cavity made up of two identical fiber Bragg gratings (FBGs), is proposed, to monitor the temperature and vibration of power transformer windings. A phase shifted gratings recoated sensor, with multilayers of polyimide films, is used to monitor the moisture content in oil. The feasibility is investigated using an experimental laboratory transformer model, especially fabricated for this application. The moisture contents are well correlated with those measured by a Karl Fisher titrator, while the values of temperature compare well with those recorded from thermocouples. It is also shown that the sensors can be used t...
Frequency response analysis (FRA) is being employed worldwide as one of the main methods for the ... more Frequency response analysis (FRA) is being employed worldwide as one of the main methods for the internal condition assessment of transformers due to its capability of detecting mechanical changes. Nonetheless, the objective interpretation of FRA measurements is still a challenge for the industry. This is mainly attributable to the lack of complete data from the same or similar units. A large database of FRA measurements can contribute to improving classification algorithms and lead to a more objective interpretation. Due to their destructive nature, mechanical deformations cannot be performed on real transformers to collect data from different scenarios. The use of simulation and laboratory transformer models is necessary. This research contribution is based on a new method using Finite Element Method simulation and a lumped element circuit to obtain FRA traces from a laboratory model at healthy and faulty states, along with an optimization method to improve capacitive parameters f...
The service of mineral insulating oils for power transformer insulation and cooling aspects canno... more The service of mineral insulating oils for power transformer insulation and cooling aspects cannot be disavowed. However, the continued use of mineral oils is questionable due to environmental unfriendliness and the divestment from fossil fuels. This has provoked the quest for green alternative insulating liquids for high-voltage insulation. Natural esters are among the remaining alternatives that are renewable and environmentally friendly. Regardless of their environmental and technical merits, natural esters have some limitations that are slowing down their total acceptance by transformer owners and utilities. Critical limitations and concerns include esters’ pour point, viscosity, oxidative stability, and ionization resistance. In this work, the state of the art of “natural esters for transformers” is explored with the aim of potential improvements. The sections of the article are geared towards technical viewpoints on improving the overall workability and serviceability of natur...
The degradation of the insulation system in liquid-filled power transformers is a serious concern... more The degradation of the insulation system in liquid-filled power transformers is a serious concern for electric power utilities. The insulation system’s ageing is accelerated by moisture, acids, oxidation products, and other decay particles (soluble and colloidal). The presence of these ageing by-products is detrimental to the insulation system and may further lead to premature ageing and serious consequences. The ageing mechanisms of oil-paper insulation are complex, highly interrelated, and strongly temperature-dependent. The operating temperature of the transformer insulating system has a direct relationship with the loading profile. The major aspect that is witnessed with the fluctuating temperatures is moisture migration and subsequent bubble evolution. In other words, gas bubbles evolve from the release of water vapor from the cellulosic insulation wrapped around the transformer windings. The models presented in the existing standards, such as the IEC Std. 60076-7:2018 and the ...
Insulation cellulose paper is a basic measure for a power transformer’s remaining useful life, an... more Insulation cellulose paper is a basic measure for a power transformer’s remaining useful life, and its advantageous low cost, electrical, and mechanical properties have made it an extensive insulation system when impregnated in a dielectric liquid. Cellulose paper deteriorates as a result of ageing due to some chemical reactions like pyrolysis (heat), hydrolysis (moisture), and oxidation (oxygen) that affects its degree of polymerization. The condition analysis of cellulose paper has been a major concern since the collection of paper samples from an operational power transformer is almost impossible. However, some chemicals generated during cellulose paper deterioration, which were dissolved in dielectric liquid, have been used alternatively for this purpose as they show a direct correlation with the paper’s degree of polymerization. Furthermore, online and non-destructive measurement of the degree of polymerization by optical sensors has been proposed recently but is yet to be avai...
In the last decades, a large focus is being placed on the sustainability and safety of the power ... more In the last decades, a large focus is being placed on the sustainability and safety of the power transformer spectrum. Ester liquids, which have interesting properties such as high fire point and biodegradability, are gaining needed attraction. Since in-service condition, thermal aging deteriorates the physicochemical and electrical properties of liquid dielectrics, it is important to study their long-term behavior. In this contribution, the pre-breakdown and breakdown behavior of ester fluids (synthetic and natural) under AC stress are investigated. Important characteristics, such as partial discharge pre-inception voltage, partial discharge inception voltage, breakdown voltage, average streamer velocity, and inception electric field, were assessed. The influence of the radius of curvature (of high voltage needle electrode) as well as the thermal degradation of typical ester liquids are also discussed. Mineral oil was also included in the tests loop as a benchmark for comparative p...
IEEE Transactions on Dielectrics and Electrical Insulation, 2021
Power transformers represent one of the most abundant and expensive components in the electric po... more Power transformers represent one of the most abundant and expensive components in the electric power industry. Dissolved gas analysis (DGA) of transformer is the most widely accepted diagnostic tool across the globe to understand insulation incipient failures. Nevertheless, DGA fault gas interpretation is a remarkable challenge for transformer owners and utility engineers. Several computational techniques have been adopted for DGA fault classification along with offline methods. However, limited data availability, high ambiguity in DGA interpretation, suitability, and model accuracy are critical challenges in the DGA fault classification using computational techniques. In this work, highly diverse and large DGA data samples of in-service transformer fleets from five different utilities have been used to develop an efficient fault classification methodology. A total of 4580 DGA samples and IEC TC 10 database are used for training and testing, respectively, for various machine learning algorithms. Discussions on performance indicators and evaluation of several algorithms to verify the most suitable class algorithms are also the focus of this work. Furthermore, a best-performing model is identified based on various performance indicators. The hyperparameters of the best model are further tuned to achieve a most precise fault classification. It is inferred that non-parametric methods and non-linear SVM are best suitable for transformer DGA fault classification. Importantly, the rankings in the present study suggest that transformer DGA fault prediction is better with ensemble learning methods.
With the growth of the world’s population and faster-developing industries, larger amounts of ele... more With the growth of the world’s population and faster-developing industries, larger amounts of electric energy are needed [...]
Electrical energy is polymorphic, with voltage levels varying between a few volts to MVs and freq... more Electrical energy is polymorphic, with voltage levels varying between a few volts to MVs and frequencies from a few Hz to MHz [...]
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Papers by Issouf Fofana