با توجه به اهمیت خطوط انتقال 400 کیلوولت و نقش اضافه ولتاژهای ناشی از صاعقه ، در این اثر با استفا... more با توجه به اهمیت خطوط انتقال 400 کیلوولت و نقش اضافه ولتاژهای ناشی از صاعقه ، در این اثر با استفاده از یک مدل دقیق فیزیکی برای شکست فاصله هوایی عایق مقره سعی شده است تا از عدم قطعیت های ناشی از استفاده از مدل های نادقیق غیرفیزیکی کاسته شود. در این اثر با استفاده از مدل های دقیق خط انتقال ، مقاومت پایه دکل و فاصله هوایی عایق خط ، مطالعه امکان سنجی تخلیه بازگشتی برای دامنه ها و شکل موج های مختلفی از صاعقه ، با استفاده از نرم افزار EMTP-RV ، به صورت موردی روی خط 400 کیلوولت دو مداره پتروشیمی فجر2- ماهشهر انجام شده است.
پیش بینی اضافه ولتاژهایی که به علت صاعقه در سیستم قدرت روی می دهند برای انتخاب مقاومت عایقی مقره ... more پیش بینی اضافه ولتاژهایی که به علت صاعقه در سیستم قدرت روی می دهند برای انتخاب مقاومت عایقی مقره های خط یک مسئله کاملا اساسی است. نرخ تخلیه خط انتقال به واسطه اضافه ولتاژ صاعقه به دو بخش نرخ خطای تخلیه بازگشتی و نرخ خطای شیلدینگ تقسیم می شود که در خطوط انتقال فشار قوی تخلیه بازگشتی بخش اعظم این نرخ خطا را تشکیل می دهد و در این مقاله تخلیه بازگشتی یک خط انتقال 230 کیلوولت بررسی شده است. در محاسبه تخلیه بازگشتی باید طبیعت تصادفی صاعقه و رفتار تصادفی مولفه های خط مانند زاویه فاز ولتاژ فرکانس قدرت در لحظه اصابت صاعقه را لحاظ کرد. به منظور لحاظ کردن این طبیعت تصادفی از روش مونت کارلو جهت بررسی عملکرد صاعقه استفاده می شود. در این مقاله با استفاده از مدل های معتبر خط انتقال، دکل، سیستم زمین و مدل فیزیکی تخلیه بازگشتی بر روی فاصله هوایی مقره، تخلیه بازگشتی به صورت موردی بر روی خط انتقال 230 کیلوولت دو مداره لوشان-دیلمان با استفاده از روش مونت کارلو مطالعه شده است.
In this paper, the exerted electric and geomagnetic forces on the electrified hydrometeors in thu... more In this paper, the exerted electric and geomagnetic forces on the electrified hydrometeors in thunderclouds are compared. The parameters of geomagnetic field are acquired from International Geomagnetic Reference Field (IGRF) model. First, the calculations showed that the magnitude of the electric force exerted on a charged hydrometeor dominated the magnitude of the geomagnetic force in troposphere. These results revealed the significance of electric force in the formation of thunderclouds’ charge structure. Moreover, as the electric field increases in thunderstorm conditions, (regarding the dependence of the induction mechanism of cloud electrification to the intensity of the electric field), the increased electric field strengthens the induction mechanism of cloud electrification and influences the electrical properties of thunderstorm. Second, using satellite-based/ground-based data and reports, an inverse relation has been revealed between the total geomagnetic field and the mean...
Abstract Humidity and pollution deposition on the surface of porcelain insulators affect the elec... more Abstract Humidity and pollution deposition on the surface of porcelain insulators affect the electrical field distribution and their performance which may lead to partial discharge and decreasing flashover voltage. Thereby one essential aspect of insulator designing is their surface science and surface wettability. To address these challenges, in this study robust omniphobic coatings were designed which can repel water and oil droplets as well as other contaminant particles from the porcelain insulators surface. In this regard, slippery liquid infused porous surface (SLIPS) coatings were applied on the porcelain substrate by infusing perfluorinated liquid lubricants into 200 %-stretched Teflon tape cover or fluoro-silanized porcelain. The surface of the designed transparent coatings repelled water, olive oil, kaolin, sodium chloride microparticles, and ice. The applied coatings exhibited low contact angle hysteresis (Δθ ≤ 5°) and a low sliding angle (α ≤ 7°) for water and olive oil droplets. SLIPS coatings showed good stability to extreme environments like immersion into acid, base, brine solutions, UV radiation and withstood at 4.5 kV inclined plane test without failure after 6 h. So, the modified SLIPS can be used as effective coatings in the porcelain insulators surface engineering.
Considering the extensive use of high voltage insulators, the reliable performance of insulators ... more Considering the extensive use of high voltage insulators, the reliable performance of insulators is challenged by various weather conditions such as pollution. According to recent researches under unidirectional wind, polymeric insulators are mostly exposed to non-uniform fan-shaped pollution. In many contamination patterns, the internal surface is covered with higher contamination than the external surface, and the non-uniform contamination shape on the insulator is similar to a ring-shape. In this paper, two conventional types of non-uniform pollution known as fan-shaped and ring-shaped are modeled for a 20 kV polymeric insulator, and a comparison is made in terms of the electric field between the two configurations using different thicknesses and electrical conductivity of the pollution layer. The electric field, during the arc length of the insulator, is studied under clean conditions, uniform contamination, and two types of non-uniform contamination. In addition, the effect of various thicknesses and conductivity of the pollution layer on the electric field distribution of this polymeric insulator is analyzed. The results show that the electric field distribution in non-uniform ring-shaped pollution is much more effective than the fan-shaped type by changing the thickness of the contamination layer. Moreover, ring-shaped pollution has a more uniform field distribution with fewer thicknesses of contamination layer.
In this paper, the measurements and modeling of the DC flashover behaviors of silicone rubber (Si... more In this paper, the measurements and modeling of the DC flashover behaviors of silicone rubber (SiR) insulators under pollution and aging conditions in the presence of surface charges have been presented. For this purpose, four different types of standard HTV-SiR insulators were selected, and then, DC flashover performance was carried out on the studied insulators in the three states including non-aged, aged, and contaminated conditions in the presence surface charges. The surfaces of the insulators were charged by an external corona source in the experimental tests, and then, the surface electric charges were measured. The experimental results of DC flashover voltage showed that the positive and negative surface charges affected flashover performance in all the states. Based on obtained empirical models of the DC flashover performance, it can be concluded that the increased aging time, positive electric charges, pollution, and average diameter reduced DC flashover performance, while the ratio of shed spacing to shed depth and negative charges enhanced the flashover voltage level.
Different methods such as mechanical, pneumatic, and electrical techniques have been used in the ... more Different methods such as mechanical, pneumatic, and electrical techniques have been used in the separation process of impurities from agricultural products. In electrical systems, three methods, that is, triboelectrostatic, free fall, and roll type with high‐voltage corona discharge electrodes, are usually used. In the present study, separation trajectory of grain and wheat straw are firstly predicted using simulation of roll‐type corona system configuration in COMSOL Multiphysics and MATLAB. Experimental tests are conducted to determine the separation performance of a roll‐type corona apparatus with 10, 15, 20, 25, and 30 kV voltages at 50, 70, and 90 rpm drum rotational speeds. The simulation results showed that the trajectory of the grain particles deviated from that of straw when the voltage increased from 10 to 30 kV as well as increasing the rotational speed from 50 to 90 rpm. Although the rotational speed of 70 rpm resulted in a good separation of grains from straw particles, increasing the speed to 90 rpm not only did not improve the separation performance but also caused a dispersal of the particles and reduced the separation quality. The simulation results were in good accordance with the experimental results obtained from the developed prototype. PRACTICAL APPLICATIONS: The results of this study can be used in configuration optimization design of “Corona Type Cylindrical Electrostatic Separation” for separating seed and straw in agriculture production, especially where they cannot be separated by conventional methods.
International Journal of Electrical Power & Energy Systems, 2019
Abstract The frequency response analysis (FRA) is a promising diagnostic method for detecting mec... more Abstract The frequency response analysis (FRA) is a promising diagnostic method for detecting mechanical faults inside a power transformer. Despite the standardization of the FRA measurement procedure, the interpretation of the results is still a subject of study. The reason lies in the fact that the frequency response is different from case to case. Therefore, for interpreting a transformer FRA result, the effects of various possible mechanical changes on the FRA trace of that particular transformer should be known. Additionally, real mechanical deformations cannot be executed for obtaining the required information due to the destructive nature. Hence, the transformer winding models are utilized instead to study the frequency response. While the circuit model has been extensively discussed in the literature, there is little focus on the numerical methods for the FRA purpose. To take a step forward, this contribution investigates the applicability of the finite integration technique for the FRA studies. The presented model can simulate different fault types for the FRA interpretation while it has also other applications regarding the frequency response. In this contribution, the FRA traces are derived directly from a finite integration model which is an important improvement compared with the previous papers. The agreement between the simulation results and the experimental data indicates that the proposed model has the potential of providing a powerful tool to decipher the transformer frequency behavior.
This paper presents experimental results of the surface charges and charge decay measurement on t... more This paper presents experimental results of the surface charges and charge decay measurement on the surface of polymeric insulator. In this research, the effect of surface charges on electric field and potential distribution has been investigated. Therefore, using measured electric charge and charge decay, the electric field and surface potential on insulator are studied by computer simulations. The accumulation of electric charge under DC electric field makes a significant difference compared to AC electric field, and this increases the rate of electrical failure and corrosion in HVDC insulators. So, a thorough understanding of the surface charge effect on insulation performance is necessary under various stresses. The experimental results revealed that the amount of charges increases linearly with the rising corona voltage and the charging time for both polarities. It was also observed that the amount of surface charges deposited by positive corona charging is less than negative corona charging. The simulation results illustrate that surface charges are important in potential and electric field variations.
This study presents two different methods under uniform and non-uniform pollution layer in order ... more This study presents two different methods under uniform and non-uniform pollution layer in order to measure and calculate the leakage current (LC) of silicone rubber insulators. Experimental test for evaluating the LC analysis of polluted insulator have been done in a laboratory clean fog chamber. The electric field and potential distributions were obtained from finite element method software for 3D models. The mathematical background and circuit theory are described in details by a section of insulator and using the extended form factor formula. The surface conductivity used in the calculations was extracted from the measured LC after wetting rate. LC characteristics under 1 : 1, 1 : 2, 1 : 5 and 1 : 10 ratios of top to bottom surface salt deposit density on polymeric insulators are studied. To verify the proposed models of this study, the results of experimental data and two other approaches are compared with together before dry-band formation. Moreover, a dynamic LC model under uniform pollution layer has been introduced and extended in order to calculate the LC when the formation of dry-bands along the insulator surface occurs. The dynamic model is drawn from experimental data and measured surface conductivity.
با توجه به اهمیت خطوط انتقال 400 کیلوولت و نقش اضافه ولتاژهای ناشی از صاعقه ، در این اثر با استفا... more با توجه به اهمیت خطوط انتقال 400 کیلوولت و نقش اضافه ولتاژهای ناشی از صاعقه ، در این اثر با استفاده از یک مدل دقیق فیزیکی برای شکست فاصله هوایی عایق مقره سعی شده است تا از عدم قطعیت های ناشی از استفاده از مدل های نادقیق غیرفیزیکی کاسته شود. در این اثر با استفاده از مدل های دقیق خط انتقال ، مقاومت پایه دکل و فاصله هوایی عایق خط ، مطالعه امکان سنجی تخلیه بازگشتی برای دامنه ها و شکل موج های مختلفی از صاعقه ، با استفاده از نرم افزار EMTP-RV ، به صورت موردی روی خط 400 کیلوولت دو مداره پتروشیمی فجر2- ماهشهر انجام شده است.
پیش بینی اضافه ولتاژهایی که به علت صاعقه در سیستم قدرت روی می دهند برای انتخاب مقاومت عایقی مقره ... more پیش بینی اضافه ولتاژهایی که به علت صاعقه در سیستم قدرت روی می دهند برای انتخاب مقاومت عایقی مقره های خط یک مسئله کاملا اساسی است. نرخ تخلیه خط انتقال به واسطه اضافه ولتاژ صاعقه به دو بخش نرخ خطای تخلیه بازگشتی و نرخ خطای شیلدینگ تقسیم می شود که در خطوط انتقال فشار قوی تخلیه بازگشتی بخش اعظم این نرخ خطا را تشکیل می دهد و در این مقاله تخلیه بازگشتی یک خط انتقال 230 کیلوولت بررسی شده است. در محاسبه تخلیه بازگشتی باید طبیعت تصادفی صاعقه و رفتار تصادفی مولفه های خط مانند زاویه فاز ولتاژ فرکانس قدرت در لحظه اصابت صاعقه را لحاظ کرد. به منظور لحاظ کردن این طبیعت تصادفی از روش مونت کارلو جهت بررسی عملکرد صاعقه استفاده می شود. در این مقاله با استفاده از مدل های معتبر خط انتقال، دکل، سیستم زمین و مدل فیزیکی تخلیه بازگشتی بر روی فاصله هوایی مقره، تخلیه بازگشتی به صورت موردی بر روی خط انتقال 230 کیلوولت دو مداره لوشان-دیلمان با استفاده از روش مونت کارلو مطالعه شده است.
In this paper, the exerted electric and geomagnetic forces on the electrified hydrometeors in thu... more In this paper, the exerted electric and geomagnetic forces on the electrified hydrometeors in thunderclouds are compared. The parameters of geomagnetic field are acquired from International Geomagnetic Reference Field (IGRF) model. First, the calculations showed that the magnitude of the electric force exerted on a charged hydrometeor dominated the magnitude of the geomagnetic force in troposphere. These results revealed the significance of electric force in the formation of thunderclouds’ charge structure. Moreover, as the electric field increases in thunderstorm conditions, (regarding the dependence of the induction mechanism of cloud electrification to the intensity of the electric field), the increased electric field strengthens the induction mechanism of cloud electrification and influences the electrical properties of thunderstorm. Second, using satellite-based/ground-based data and reports, an inverse relation has been revealed between the total geomagnetic field and the mean...
Abstract Humidity and pollution deposition on the surface of porcelain insulators affect the elec... more Abstract Humidity and pollution deposition on the surface of porcelain insulators affect the electrical field distribution and their performance which may lead to partial discharge and decreasing flashover voltage. Thereby one essential aspect of insulator designing is their surface science and surface wettability. To address these challenges, in this study robust omniphobic coatings were designed which can repel water and oil droplets as well as other contaminant particles from the porcelain insulators surface. In this regard, slippery liquid infused porous surface (SLIPS) coatings were applied on the porcelain substrate by infusing perfluorinated liquid lubricants into 200 %-stretched Teflon tape cover or fluoro-silanized porcelain. The surface of the designed transparent coatings repelled water, olive oil, kaolin, sodium chloride microparticles, and ice. The applied coatings exhibited low contact angle hysteresis (Δθ ≤ 5°) and a low sliding angle (α ≤ 7°) for water and olive oil droplets. SLIPS coatings showed good stability to extreme environments like immersion into acid, base, brine solutions, UV radiation and withstood at 4.5 kV inclined plane test without failure after 6 h. So, the modified SLIPS can be used as effective coatings in the porcelain insulators surface engineering.
Considering the extensive use of high voltage insulators, the reliable performance of insulators ... more Considering the extensive use of high voltage insulators, the reliable performance of insulators is challenged by various weather conditions such as pollution. According to recent researches under unidirectional wind, polymeric insulators are mostly exposed to non-uniform fan-shaped pollution. In many contamination patterns, the internal surface is covered with higher contamination than the external surface, and the non-uniform contamination shape on the insulator is similar to a ring-shape. In this paper, two conventional types of non-uniform pollution known as fan-shaped and ring-shaped are modeled for a 20 kV polymeric insulator, and a comparison is made in terms of the electric field between the two configurations using different thicknesses and electrical conductivity of the pollution layer. The electric field, during the arc length of the insulator, is studied under clean conditions, uniform contamination, and two types of non-uniform contamination. In addition, the effect of various thicknesses and conductivity of the pollution layer on the electric field distribution of this polymeric insulator is analyzed. The results show that the electric field distribution in non-uniform ring-shaped pollution is much more effective than the fan-shaped type by changing the thickness of the contamination layer. Moreover, ring-shaped pollution has a more uniform field distribution with fewer thicknesses of contamination layer.
In this paper, the measurements and modeling of the DC flashover behaviors of silicone rubber (Si... more In this paper, the measurements and modeling of the DC flashover behaviors of silicone rubber (SiR) insulators under pollution and aging conditions in the presence of surface charges have been presented. For this purpose, four different types of standard HTV-SiR insulators were selected, and then, DC flashover performance was carried out on the studied insulators in the three states including non-aged, aged, and contaminated conditions in the presence surface charges. The surfaces of the insulators were charged by an external corona source in the experimental tests, and then, the surface electric charges were measured. The experimental results of DC flashover voltage showed that the positive and negative surface charges affected flashover performance in all the states. Based on obtained empirical models of the DC flashover performance, it can be concluded that the increased aging time, positive electric charges, pollution, and average diameter reduced DC flashover performance, while the ratio of shed spacing to shed depth and negative charges enhanced the flashover voltage level.
Different methods such as mechanical, pneumatic, and electrical techniques have been used in the ... more Different methods such as mechanical, pneumatic, and electrical techniques have been used in the separation process of impurities from agricultural products. In electrical systems, three methods, that is, triboelectrostatic, free fall, and roll type with high‐voltage corona discharge electrodes, are usually used. In the present study, separation trajectory of grain and wheat straw are firstly predicted using simulation of roll‐type corona system configuration in COMSOL Multiphysics and MATLAB. Experimental tests are conducted to determine the separation performance of a roll‐type corona apparatus with 10, 15, 20, 25, and 30 kV voltages at 50, 70, and 90 rpm drum rotational speeds. The simulation results showed that the trajectory of the grain particles deviated from that of straw when the voltage increased from 10 to 30 kV as well as increasing the rotational speed from 50 to 90 rpm. Although the rotational speed of 70 rpm resulted in a good separation of grains from straw particles, increasing the speed to 90 rpm not only did not improve the separation performance but also caused a dispersal of the particles and reduced the separation quality. The simulation results were in good accordance with the experimental results obtained from the developed prototype. PRACTICAL APPLICATIONS: The results of this study can be used in configuration optimization design of “Corona Type Cylindrical Electrostatic Separation” for separating seed and straw in agriculture production, especially where they cannot be separated by conventional methods.
International Journal of Electrical Power & Energy Systems, 2019
Abstract The frequency response analysis (FRA) is a promising diagnostic method for detecting mec... more Abstract The frequency response analysis (FRA) is a promising diagnostic method for detecting mechanical faults inside a power transformer. Despite the standardization of the FRA measurement procedure, the interpretation of the results is still a subject of study. The reason lies in the fact that the frequency response is different from case to case. Therefore, for interpreting a transformer FRA result, the effects of various possible mechanical changes on the FRA trace of that particular transformer should be known. Additionally, real mechanical deformations cannot be executed for obtaining the required information due to the destructive nature. Hence, the transformer winding models are utilized instead to study the frequency response. While the circuit model has been extensively discussed in the literature, there is little focus on the numerical methods for the FRA purpose. To take a step forward, this contribution investigates the applicability of the finite integration technique for the FRA studies. The presented model can simulate different fault types for the FRA interpretation while it has also other applications regarding the frequency response. In this contribution, the FRA traces are derived directly from a finite integration model which is an important improvement compared with the previous papers. The agreement between the simulation results and the experimental data indicates that the proposed model has the potential of providing a powerful tool to decipher the transformer frequency behavior.
This paper presents experimental results of the surface charges and charge decay measurement on t... more This paper presents experimental results of the surface charges and charge decay measurement on the surface of polymeric insulator. In this research, the effect of surface charges on electric field and potential distribution has been investigated. Therefore, using measured electric charge and charge decay, the electric field and surface potential on insulator are studied by computer simulations. The accumulation of electric charge under DC electric field makes a significant difference compared to AC electric field, and this increases the rate of electrical failure and corrosion in HVDC insulators. So, a thorough understanding of the surface charge effect on insulation performance is necessary under various stresses. The experimental results revealed that the amount of charges increases linearly with the rising corona voltage and the charging time for both polarities. It was also observed that the amount of surface charges deposited by positive corona charging is less than negative corona charging. The simulation results illustrate that surface charges are important in potential and electric field variations.
This study presents two different methods under uniform and non-uniform pollution layer in order ... more This study presents two different methods under uniform and non-uniform pollution layer in order to measure and calculate the leakage current (LC) of silicone rubber insulators. Experimental test for evaluating the LC analysis of polluted insulator have been done in a laboratory clean fog chamber. The electric field and potential distributions were obtained from finite element method software for 3D models. The mathematical background and circuit theory are described in details by a section of insulator and using the extended form factor formula. The surface conductivity used in the calculations was extracted from the measured LC after wetting rate. LC characteristics under 1 : 1, 1 : 2, 1 : 5 and 1 : 10 ratios of top to bottom surface salt deposit density on polymeric insulators are studied. To verify the proposed models of this study, the results of experimental data and two other approaches are compared with together before dry-band formation. Moreover, a dynamic LC model under uniform pollution layer has been introduced and extended in order to calculate the LC when the formation of dry-bands along the insulator surface occurs. The dynamic model is drawn from experimental data and measured surface conductivity.
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