An 800 kV electric power substation can have more than one hundred of porcelain multicone type insulators supporting busbar structures.Two or more sections in series,having middle and end fittings,compose these insula...An 800 kV electric power substation can have more than one hundred of porcelain multicone type insulators supporting busbar structures.Two or more sections in series,having middle and end fittings,compose these insulators.Ageing process can cause degradation of the cement used in this type of insulator and this fact can affect its dielectric performance under heavy rain.This paper presents results of an investigation based on power frequency high voltage tests performed on 800 kV porcelain multicone type insulators,removed from service after having operated for more than 20 years,as well a non-used one that had been stored on site for long time.The insulators were tested in different arrangements:each section at a time and the two sections assembled in series,as actually used insulator columns.The tests were carried out under artificial rain ranging from 1 mm/min to 5 mm/min.The results have confirmed a reduction of up to 30% in the insulator power frequency flashover voltage under 5 mm/min rain conditions and gave important information to the utility about radial cracks that were observed in many insulators and about the discharge mechanisms along the insulators under rain.展开更多
Under conditions of atmospheric blocking, the presence of a quasi-stationary anticyclone of large amplitude disrupts the normal eastward progression of the synoptic systems. These blockings correspond mainly to a posi...Under conditions of atmospheric blocking, the presence of a quasi-stationary anticyclone of large amplitude disrupts the normal eastward progression of the synoptic systems. These blockings correspond mainly to a positive anomaly of the air pressure. As a result, in the regions affected by the blocking occur several consecutive dry days and temperatures above average. This paper aims to discuss synoptically the atmospheric blocking phenomenon occurred in January and February 2014 in the South Atlantic Ocean, affecting especially the Southeastern Brazil and sectors that depend on the quantity of water for their activities in the region, such as agriculture and electricity generation. The significant population concentration makes this area emphatically vulnerable to long periods of drought, especially during the summer, affecting the water supply for the population. In order to achieve this goal, data of geopotential height at 850/500 hPa, streamlines in 850/500 hPa, pressure, temperature, humidity and wind at surface were evaluated through NCEP/ NCAR reanalysis (CFSRv2—Climate Forecast System Reanalysis Version 2) with 0.2° × 0.2° resolution. The analysis showed that the stationary anticyclone was configured dynamically favorable to blocking in the lower and middle levels of the atmosphere. Thus, atmospheric pressure at mean sea level presented values above normal combined with high average air temperature. By the climatological analysis, it was noted that there were emphatic negative precipitation anomalies over Southeastern Brazil. This atmospheric blocking was characterized as anomalous due to its long duration in a considered rainy season.展开更多
Hot-dip galvanized steel is one of the most used materials in equipment and metallic structures of the Brazilian electric sector. Although carbon steel is the main substrate in the galvanizing hot-dip process, recentl...Hot-dip galvanized steel is one of the most used materials in equipment and metallic structures of the Brazilian electric sector. Although carbon steel is the main substrate in the galvanizing hot-dip process, recently, weathering steel has been used as an alternative material to be galvanized. In the transmission line segment of the Brazilian electric sector, for instance, compact towers made of galvanized weathering steel have been installed to conduct energy through urban sites. It is well known that weathering steel, depending on wet and dry cycles and on the pollutants present in the atmosphere, develops a protective patina made of its corrosion products. The patina is dense and strongly adhered to the substrate, blocking the active surface and, thus, reducing the corrosion rate of the base metal. However, when the weathering steel is galvanized, the substrate surface has a layer of zinc and zinc-iron intermetallic alloys. When the sacrificial layer is consumed by atmospheric corrosion, critical questions remain to be answered regarding the underlying substrate. Will the patina of weathering steel be formed? In what condition? Does the hot-dip galvanizing process modify the weathering steel microstructure? The present work carried out an experimental research to shed light on the anticorrosive behavior of hot-dip galvanized weathering steel, after the zinc layer is corroded. This was done by a controlled pickling process, where the zinc layer was removed simulating its consumption during real corrosion processes. The results, obtained through electrochemical techniques and different accelerated corrosion tests, showed that galvanizing weathering steel is a promising technology to enhance the lifetime of structures used in the Brazilian electric sector.展开更多
The mechanism of corrosion is mainly sustained by an electrochemical process, in which anodic and cathodic reactions take place, keeping their kinetics alive by electrons and ions fluxes. Several specific conditions c...The mechanism of corrosion is mainly sustained by an electrochemical process, in which anodic and cathodic reactions take place, keeping their kinetics alive by electrons and ions fluxes. Several specific conditions can accelerate corrosion processes. When studying anticorrosive coatings, one of them is the contamination of metallic surface by soluble salts prior to coating, leading to premature failure of the paint system due to corrosion between the metallic surface and the coating. So the surface preparation step prior to coating is a procedure of great importance to the coating anticorrosive performance. The aim of this step is to clean the surface by removing visible and non-visible contaminants. Usually, wet abrasive blasting methods are the most efficient ones to achieve the latter objective, because they may clean the surface, create a surface roughness and also remove the non-visible contaminants, as they use water as a media. On the other hand, evaporation of water after blasting may create flash rust and to avoid this, it is common to use corrosion inhibitors in the water of wet blasting methods. In this paper, the use of sodium tetraborate (borax) as a corrosion inhibitor in wet abrasive blasting is discussed. Electrochemical measurements and mass loss tests show that a borax content of 1% in a saline solution has the best inhibitory action over carbon steel and zinc surfaces, allowing postponing for the painting step some time. However, residual borax left on the surface generated blistering and corrosion under coating, during accelerated corrosion test in a humidity condensation chamber. Electrochemical impedance spectroscopy confirmed that borax accelerated the permeation of water through the coating, downgrading the anticorrosive performance of the paint system.展开更多
This paper presents a software for simulating the thermal performance of solar water heating systems. The implemented model computes the energy balance in the hot water storage tank in each time step along a simulatio...This paper presents a software for simulating the thermal performance of solar water heating systems. The implemented model computes the energy balance in the hot water storage tank in each time step along a simulation interval. Its input data are values from a typical meteorological year of a chosen location and the hot water load. The system components are the hot water storage tank and the solar collector. Firstly, the validation of the model is presented and then four solar water heating systems are simulated in four different cities along one year. The storage tank water hourly temperatures were obtained for a typical meteorological year and those values were compared with the values obtained by the widespread TRNSYS simulation software. The results obtained from this comparison were satisfactory.展开更多
1|INTRODUCTION The new-type power system,with a strong,intelligent and flexible grid as its hub platform,is a key carrier for achieving the goals of carbon peak and carbon neutrality.Among them,AC/DC transmission and ...1|INTRODUCTION The new-type power system,with a strong,intelligent and flexible grid as its hub platform,is a key carrier for achieving the goals of carbon peak and carbon neutrality.Among them,AC/DC transmission and distribution equipment is the core for achieving power conversion and transmission.In order to adapt to the high proportion of new energy,large-scale energy storage,and diversified flexible load,and to promote the high-quality construction of the new-type power system,it is urgent to carry out research and devel-opment on flexible and intelligent new transmission and distribution equipment.展开更多
This paper introduces the new class of periodic multivariate GARCH models in their periodic BEKK specification.Semi-polynomial Markov chains combined with algebraic geometry are used to obtain some properties like irr...This paper introduces the new class of periodic multivariate GARCH models in their periodic BEKK specification.Semi-polynomial Markov chains combined with algebraic geometry are used to obtain some properties like irreducibility.We impose weak conditions to obtain the strict periodic stationarity and the geometric ergodicity of the process,via the theory of positive linear operators on a cone:it is supposed that zero belongs to the support of the driving noise density which is absolutely continuous with respect to the Lebesgue measure and the spectral radius of a matrix built from the periodic coefficients of the model is smaller than one.展开更多
Power reversal control strategies for different types of hybrid line-commutated-converter(LCC)/modular multi-level converter(MMC)based high-voltage direct-current(HVDC)systems have been proposed with the consideration...Power reversal control strategies for different types of hybrid line-commutated-converter(LCC)/modular multi-level converter(MMC)based high-voltage direct-current(HVDC)systems have been proposed with the consideration of system configurations and MMC’s topologies.The studies show that the full-bridge(FB)MMC gives better performance than half-bridge(HB)MMCs in terms of power reversal in hybrid LCC/MMC systems.The modulation method employed in this paper can achieve a smooth online polarity reversal for hybrid LCC/FB-MMC HVDC systems.Additional DC switches and/or discharging resistors may be needed to reverse the DC polarity of LCC/HB-MMC HVDC systems.Based on the proposed strate-gies,the power reversal processes of the studied systems can be accomplished within several seconds.The speed can be changed according to system operation requirements.The effectiveness of the proposed control strategies has been verified through simulations conducted in PSCAD/EMTDC.展开更多
Several substations in operation were commissioned decades ago.These substations are overstressed,then their protection equipment cannot provide an effective safety condition to the system.In the worst cases,short‐ci...Several substations in operation were commissioned decades ago.These substations are overstressed,then their protection equipment cannot provide an effective safety condition to the system.In the worst cases,short‐circuits can cause permanent damage to the system if the overcurrent is higher than the capacity of the installed equipment.There are some possible solutions for those cases:replace all the equipment in the overstressed substation,build a new one in parallel or install a fault current limiter(FCL)device.From an economic point of view,introducing FCLs in the power system is the best way to solve the described problem.The commercial solutions available are the pyrotechnic FCL,air coil reactor,neutral earthing resistor,and high impedance transformer.However,these devices are limited and present several drawbacks.Since the’70s,there has been a search for reliable FCL devices that do not interfere in the regular operation of substations and could limit the fault currents to the protection system rated level.There were so many FCL technologies proposed in the last decades.These proposed new devices may use superconducting technologies,power electronics,or both.This paper reviews proven FCL technologies,focusing on full‐scale devices demonstrated in field and lab tests.The goal is to introduce the main FCL technologies in development and discuss didactically their operation principle,the built prototypes,the commercial units,whether they exist,and the main drawbacks for each technology presented.A final analysis of the level of maturity for each FCL technology is discussed using the TRL(Technology readiness level)scale in order to find technologies with more potential for mass production.The three technologies closer to the full commercial application are:the Resistive Superconducting FCL,the Saturated Iron Core FCL,and the Series Reactor FCL.展开更多
文摘An 800 kV electric power substation can have more than one hundred of porcelain multicone type insulators supporting busbar structures.Two or more sections in series,having middle and end fittings,compose these insulators.Ageing process can cause degradation of the cement used in this type of insulator and this fact can affect its dielectric performance under heavy rain.This paper presents results of an investigation based on power frequency high voltage tests performed on 800 kV porcelain multicone type insulators,removed from service after having operated for more than 20 years,as well a non-used one that had been stored on site for long time.The insulators were tested in different arrangements:each section at a time and the two sections assembled in series,as actually used insulator columns.The tests were carried out under artificial rain ranging from 1 mm/min to 5 mm/min.The results have confirmed a reduction of up to 30% in the insulator power frequency flashover voltage under 5 mm/min rain conditions and gave important information to the utility about radial cracks that were observed in many insulators and about the discharge mechanisms along the insulators under rain.
文摘Under conditions of atmospheric blocking, the presence of a quasi-stationary anticyclone of large amplitude disrupts the normal eastward progression of the synoptic systems. These blockings correspond mainly to a positive anomaly of the air pressure. As a result, in the regions affected by the blocking occur several consecutive dry days and temperatures above average. This paper aims to discuss synoptically the atmospheric blocking phenomenon occurred in January and February 2014 in the South Atlantic Ocean, affecting especially the Southeastern Brazil and sectors that depend on the quantity of water for their activities in the region, such as agriculture and electricity generation. The significant population concentration makes this area emphatically vulnerable to long periods of drought, especially during the summer, affecting the water supply for the population. In order to achieve this goal, data of geopotential height at 850/500 hPa, streamlines in 850/500 hPa, pressure, temperature, humidity and wind at surface were evaluated through NCEP/ NCAR reanalysis (CFSRv2—Climate Forecast System Reanalysis Version 2) with 0.2° × 0.2° resolution. The analysis showed that the stationary anticyclone was configured dynamically favorable to blocking in the lower and middle levels of the atmosphere. Thus, atmospheric pressure at mean sea level presented values above normal combined with high average air temperature. By the climatological analysis, it was noted that there were emphatic negative precipitation anomalies over Southeastern Brazil. This atmospheric blocking was characterized as anomalous due to its long duration in a considered rainy season.
文摘Hot-dip galvanized steel is one of the most used materials in equipment and metallic structures of the Brazilian electric sector. Although carbon steel is the main substrate in the galvanizing hot-dip process, recently, weathering steel has been used as an alternative material to be galvanized. In the transmission line segment of the Brazilian electric sector, for instance, compact towers made of galvanized weathering steel have been installed to conduct energy through urban sites. It is well known that weathering steel, depending on wet and dry cycles and on the pollutants present in the atmosphere, develops a protective patina made of its corrosion products. The patina is dense and strongly adhered to the substrate, blocking the active surface and, thus, reducing the corrosion rate of the base metal. However, when the weathering steel is galvanized, the substrate surface has a layer of zinc and zinc-iron intermetallic alloys. When the sacrificial layer is consumed by atmospheric corrosion, critical questions remain to be answered regarding the underlying substrate. Will the patina of weathering steel be formed? In what condition? Does the hot-dip galvanizing process modify the weathering steel microstructure? The present work carried out an experimental research to shed light on the anticorrosive behavior of hot-dip galvanized weathering steel, after the zinc layer is corroded. This was done by a controlled pickling process, where the zinc layer was removed simulating its consumption during real corrosion processes. The results, obtained through electrochemical techniques and different accelerated corrosion tests, showed that galvanizing weathering steel is a promising technology to enhance the lifetime of structures used in the Brazilian electric sector.
文摘The mechanism of corrosion is mainly sustained by an electrochemical process, in which anodic and cathodic reactions take place, keeping their kinetics alive by electrons and ions fluxes. Several specific conditions can accelerate corrosion processes. When studying anticorrosive coatings, one of them is the contamination of metallic surface by soluble salts prior to coating, leading to premature failure of the paint system due to corrosion between the metallic surface and the coating. So the surface preparation step prior to coating is a procedure of great importance to the coating anticorrosive performance. The aim of this step is to clean the surface by removing visible and non-visible contaminants. Usually, wet abrasive blasting methods are the most efficient ones to achieve the latter objective, because they may clean the surface, create a surface roughness and also remove the non-visible contaminants, as they use water as a media. On the other hand, evaporation of water after blasting may create flash rust and to avoid this, it is common to use corrosion inhibitors in the water of wet blasting methods. In this paper, the use of sodium tetraborate (borax) as a corrosion inhibitor in wet abrasive blasting is discussed. Electrochemical measurements and mass loss tests show that a borax content of 1% in a saline solution has the best inhibitory action over carbon steel and zinc surfaces, allowing postponing for the painting step some time. However, residual borax left on the surface generated blistering and corrosion under coating, during accelerated corrosion test in a humidity condensation chamber. Electrochemical impedance spectroscopy confirmed that borax accelerated the permeation of water through the coating, downgrading the anticorrosive performance of the paint system.
文摘This paper presents a software for simulating the thermal performance of solar water heating systems. The implemented model computes the energy balance in the hot water storage tank in each time step along a simulation interval. Its input data are values from a typical meteorological year of a chosen location and the hot water load. The system components are the hot water storage tank and the solar collector. Firstly, the validation of the model is presented and then four solar water heating systems are simulated in four different cities along one year. The storage tank water hourly temperatures were obtained for a typical meteorological year and those values were compared with the values obtained by the widespread TRNSYS simulation software. The results obtained from this comparison were satisfactory.
文摘1|INTRODUCTION The new-type power system,with a strong,intelligent and flexible grid as its hub platform,is a key carrier for achieving the goals of carbon peak and carbon neutrality.Among them,AC/DC transmission and distribution equipment is the core for achieving power conversion and transmission.In order to adapt to the high proportion of new energy,large-scale energy storage,and diversified flexible load,and to promote the high-quality construction of the new-type power system,it is urgent to carry out research and devel-opment on flexible and intelligent new transmission and distribution equipment.
基金the support of the University of Science and Technology Houari Boumediene (USTHB) and the Ministry of Higher Education and Scientific Research, Algiers, Algeria for the PNR 25/08the support of the University of Médéa, Algeria
文摘This paper introduces the new class of periodic multivariate GARCH models in their periodic BEKK specification.Semi-polynomial Markov chains combined with algebraic geometry are used to obtain some properties like irreducibility.We impose weak conditions to obtain the strict periodic stationarity and the geometric ergodicity of the process,via the theory of positive linear operators on a cone:it is supposed that zero belongs to the support of the driving noise density which is absolutely continuous with respect to the Lebesgue measure and the spectral radius of a matrix built from the periodic coefficients of the model is smaller than one.
基金This work was supported by Science and Technology Project of the State Grid Corporation of China,“HVDC Systems/Grids for Transnational Interconnections”,project number:SGTYHT/16-JS-198.
文摘Power reversal control strategies for different types of hybrid line-commutated-converter(LCC)/modular multi-level converter(MMC)based high-voltage direct-current(HVDC)systems have been proposed with the consideration of system configurations and MMC’s topologies.The studies show that the full-bridge(FB)MMC gives better performance than half-bridge(HB)MMCs in terms of power reversal in hybrid LCC/MMC systems.The modulation method employed in this paper can achieve a smooth online polarity reversal for hybrid LCC/FB-MMC HVDC systems.Additional DC switches and/or discharging resistors may be needed to reverse the DC polarity of LCC/HB-MMC HVDC systems.Based on the proposed strate-gies,the power reversal processes of the studied systems can be accomplished within several seconds.The speed can be changed according to system operation requirements.The effectiveness of the proposed control strategies has been verified through simulations conducted in PSCAD/EMTDC.
文摘Several substations in operation were commissioned decades ago.These substations are overstressed,then their protection equipment cannot provide an effective safety condition to the system.In the worst cases,short‐circuits can cause permanent damage to the system if the overcurrent is higher than the capacity of the installed equipment.There are some possible solutions for those cases:replace all the equipment in the overstressed substation,build a new one in parallel or install a fault current limiter(FCL)device.From an economic point of view,introducing FCLs in the power system is the best way to solve the described problem.The commercial solutions available are the pyrotechnic FCL,air coil reactor,neutral earthing resistor,and high impedance transformer.However,these devices are limited and present several drawbacks.Since the’70s,there has been a search for reliable FCL devices that do not interfere in the regular operation of substations and could limit the fault currents to the protection system rated level.There were so many FCL technologies proposed in the last decades.These proposed new devices may use superconducting technologies,power electronics,or both.This paper reviews proven FCL technologies,focusing on full‐scale devices demonstrated in field and lab tests.The goal is to introduce the main FCL technologies in development and discuss didactically their operation principle,the built prototypes,the commercial units,whether they exist,and the main drawbacks for each technology presented.A final analysis of the level of maturity for each FCL technology is discussed using the TRL(Technology readiness level)scale in order to find technologies with more potential for mass production.The three technologies closer to the full commercial application are:the Resistive Superconducting FCL,the Saturated Iron Core FCL,and the Series Reactor FCL.
