2015 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), 2015
Flashover behaviour of silicone rubber insulators were analysed under contaminated conditions in ... more Flashover behaviour of silicone rubber insulators were analysed under contaminated conditions in this paper. The modified IEC 60507 Standard was used to simulate pollution deposition on the insulator surface. Experiments were carried out at different pollution level and changing leakage distances to investigate the behaviour of silicone rubber insulators. It was shown experimentally that flashover voltage is highly dependent on pollution level and leakage distance. The result of this study can be used to investigate the ageing of silicone rubber insulators and their selection for contaminated and wet environments.
2006 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2006
The arc behavior and its propagation mechanism on pre-contaminated insulator surfaces covered wit... more The arc behavior and its propagation mechanism on pre-contaminated insulator surfaces covered with ice were investigated and are presented in this paper. Using a simplified cylindrical physical model, the arc characteristics were determined. Intervening factors and parameters such as arc length and ice thickness were studied. These results will serve to extend the mathematical model previously developed at CIGELE for
CEIDP '05. 2005 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2005., 2005
This paper aims to study the electrical behavior of snow for the purpose of developing an analyti... more This paper aims to study the electrical behavior of snow for the purpose of developing an analytical model. Laboratory tests on a snow-covered polymer insulator string were carried out under high alternative voltage. The voltage-current characteristics of snow were analyzed, showing that voltage across snow is a logarithmic function of leakage current depending on snow density and melted conductivity. It
2009 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2009
Results of the first studies of arc on an ice surface by time-resolved spectral analysis with a g... more Results of the first studies of arc on an ice surface by time-resolved spectral analysis with a good time and wavelength resolution have been obtained and are reported in this paper. Time-resolved spectra were recorded at different stages of arc propagation on an ice surface in order to obtain information on the occurring ionization processes. Moreover, the emission features of
POWERCON '98. 1998 International Conference on Power System Technology. Proceedings (Cat. No.98EX151)
The main purpose of the present paper is to investigate the effects of high altitude on AC flasho... more The main purpose of the present paper is to investigate the effects of high altitude on AC flashover of a short insulator covered with ice. The experiments were carried out in an evacuated chamber in which the air pressure condition at high altitude up to 9000 m may be simulated. It was found that low pressure at high altitudes could
Low air pressure and recurrent icing may affect the discharge characteristics of dielectrics and ... more Low air pressure and recurrent icing may affect the discharge characteristics of dielectrics and decrease the insulating performance of insulators. The aim of this paper is to investigate the corona discharge phenomena on ice-covered insulators at low air pressure based on an icicle/iced-plate electrode system with direct current (DC) positive voltage. Using a pulse current sensor and an ultraviolet camera, CoroCAM IV+, it was possible to carry out investigations on the influence of atmospheric pressure on corona onset voltage, discharge mode, discharge waveform and mean discharge amplitude. An empirical function for predicting corona onset voltage was developed, shedding more light on the influence of pressure on mean pulse amplitude of partial discharge (PD). The theoretical analysis indicates that the corona onset voltage of the tested clearance decreases exponentially with the increase of altitude, and that the special exponents are affected by the length of clearance. The resul...
2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2012
ABSTRACT Spectra of the emitted light from an arc formed on an ice surface over a wide range (300... more ABSTRACT Spectra of the emitted light from an arc formed on an ice surface over a wide range (300-850 nm) were studied using a triggered spectrometer. Detailed analysis of the spectra allowed identifying different atomic lines and molecular bands from the background gases, as well as excited species from polluted ice. Time-resolved spectra were recorded at different stages of arc propagation over an ice surface to gather data on the occurring ionization processes. From comparisons of overall spectra of white and flashover arcs, it was observed that a white arc emits light mostly in the ultraviolet region, whereas a flashover arc emits light mostly in the visible region. It was pointed out that the intensity of some lines, such as copper, increases constantly between the white arc and flashover occurrences. However, the intensity of some lines, such as Hα and Hβ and N2+ first negative, increases suddenly during flashover. The possible chemical reactions responsible for emitting observed lines and bands were discussed.
IEEE Transactions on Dielectrics and Electrical Insulation, 2000
Using a high-speed camera, the fundamental behavior of arcs on ice surfaces, including propagatio... more Using a high-speed camera, the fundamental behavior of arcs on ice surfaces, including propagation velocity and root radii were studied under both ac and dc voltages. It was found that the arc may propagate randomly inside or outside of the ice with a relatively low velocity before the critical length is reached, and then at a much higher velocity. Moreover,
The main objective of the present study is to further our understanding of the influence of ambie... more The main objective of the present study is to further our understanding of the influence of ambient temperature, freezing water conductivity and nature of applied voltage on the surface flashover of ice. Flashover tests were carried out using two metallic hemispherical capped rods 12 mm in diameter, separated by an ice surface. The distance between the electrodes was 18 mm. Ice surface flashover voltage was determined under alternating, DC-positive and DC-negative voltages using a method based on 50% withstand voltage. The results obtained show that flashover voltage on ice surfaces decreases with an increase in ambient temperature and freezing water conductivity. Moreover, flashover voltage depends on the nature of the applied voltage. q 1998 Elsevier Science B.V.
2009 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2009
Positive dc arc propagation on an ice surface was studied by high speed photography and simultane... more Positive dc arc propagation on an ice surface was studied by high speed photography and simultaneous measurement of leakage current and voltage. All experiments were performed on a 120-cm long simplified physical model simulating real ice-covered insulators. Some features of the arc development pattern like minor and major arc collapses and the effects of arc propagation direction were examined. Previous
A laboratory study of ice accretion from supercooled droplets on energized insulators was investi... more A laboratory study of ice accretion from supercooled droplets on energized insulators was investigated. Wet ice, which is associated with the highest probability of flashover, was produced at temperatures of _12°C and _7°C with water droplets of 50 and 80 11m and liquid water contents of 4.4 and 6.8 g.m-3. Wind velocity and the conductivity of freezing water played important roles in the uniformity and roughness of ice accreted, respectively. It was also found that the mean power fed to the insulators by conduction current and corona discharges was about 40% of heat power liberated by the freezing process during wet ice accretion.
In today’s economic climate, it is important to know the condition, by means of suitable diagnost... more In today’s economic climate, it is important to know the condition, by means of suitable diagnostic tests, of the oil impregnated paper usable as primary insulation in equipment such as transformers, switchgear, bushings, cables and their accessories. The aim of this paper is regarded as a main task to study the parameters that mostly influence life time of Aramid paper built high voltage transformers. It is shown that the initial moisture content of Aramid paper as well as the metallic catalysts seem to have practically no influence on the aging process. The presence of oxygen however markedly increases the degradation rate.
2015 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), 2015
Flashover behaviour of silicone rubber insulators were analysed under contaminated conditions in ... more Flashover behaviour of silicone rubber insulators were analysed under contaminated conditions in this paper. The modified IEC 60507 Standard was used to simulate pollution deposition on the insulator surface. Experiments were carried out at different pollution level and changing leakage distances to investigate the behaviour of silicone rubber insulators. It was shown experimentally that flashover voltage is highly dependent on pollution level and leakage distance. The result of this study can be used to investigate the ageing of silicone rubber insulators and their selection for contaminated and wet environments.
2006 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2006
The arc behavior and its propagation mechanism on pre-contaminated insulator surfaces covered wit... more The arc behavior and its propagation mechanism on pre-contaminated insulator surfaces covered with ice were investigated and are presented in this paper. Using a simplified cylindrical physical model, the arc characteristics were determined. Intervening factors and parameters such as arc length and ice thickness were studied. These results will serve to extend the mathematical model previously developed at CIGELE for
CEIDP '05. 2005 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2005., 2005
This paper aims to study the electrical behavior of snow for the purpose of developing an analyti... more This paper aims to study the electrical behavior of snow for the purpose of developing an analytical model. Laboratory tests on a snow-covered polymer insulator string were carried out under high alternative voltage. The voltage-current characteristics of snow were analyzed, showing that voltage across snow is a logarithmic function of leakage current depending on snow density and melted conductivity. It
2009 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2009
Results of the first studies of arc on an ice surface by time-resolved spectral analysis with a g... more Results of the first studies of arc on an ice surface by time-resolved spectral analysis with a good time and wavelength resolution have been obtained and are reported in this paper. Time-resolved spectra were recorded at different stages of arc propagation on an ice surface in order to obtain information on the occurring ionization processes. Moreover, the emission features of
POWERCON '98. 1998 International Conference on Power System Technology. Proceedings (Cat. No.98EX151)
The main purpose of the present paper is to investigate the effects of high altitude on AC flasho... more The main purpose of the present paper is to investigate the effects of high altitude on AC flashover of a short insulator covered with ice. The experiments were carried out in an evacuated chamber in which the air pressure condition at high altitude up to 9000 m may be simulated. It was found that low pressure at high altitudes could
Low air pressure and recurrent icing may affect the discharge characteristics of dielectrics and ... more Low air pressure and recurrent icing may affect the discharge characteristics of dielectrics and decrease the insulating performance of insulators. The aim of this paper is to investigate the corona discharge phenomena on ice-covered insulators at low air pressure based on an icicle/iced-plate electrode system with direct current (DC) positive voltage. Using a pulse current sensor and an ultraviolet camera, CoroCAM IV+, it was possible to carry out investigations on the influence of atmospheric pressure on corona onset voltage, discharge mode, discharge waveform and mean discharge amplitude. An empirical function for predicting corona onset voltage was developed, shedding more light on the influence of pressure on mean pulse amplitude of partial discharge (PD). The theoretical analysis indicates that the corona onset voltage of the tested clearance decreases exponentially with the increase of altitude, and that the special exponents are affected by the length of clearance. The resul...
2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2012
ABSTRACT Spectra of the emitted light from an arc formed on an ice surface over a wide range (300... more ABSTRACT Spectra of the emitted light from an arc formed on an ice surface over a wide range (300-850 nm) were studied using a triggered spectrometer. Detailed analysis of the spectra allowed identifying different atomic lines and molecular bands from the background gases, as well as excited species from polluted ice. Time-resolved spectra were recorded at different stages of arc propagation over an ice surface to gather data on the occurring ionization processes. From comparisons of overall spectra of white and flashover arcs, it was observed that a white arc emits light mostly in the ultraviolet region, whereas a flashover arc emits light mostly in the visible region. It was pointed out that the intensity of some lines, such as copper, increases constantly between the white arc and flashover occurrences. However, the intensity of some lines, such as Hα and Hβ and N2+ first negative, increases suddenly during flashover. The possible chemical reactions responsible for emitting observed lines and bands were discussed.
IEEE Transactions on Dielectrics and Electrical Insulation, 2000
Using a high-speed camera, the fundamental behavior of arcs on ice surfaces, including propagatio... more Using a high-speed camera, the fundamental behavior of arcs on ice surfaces, including propagation velocity and root radii were studied under both ac and dc voltages. It was found that the arc may propagate randomly inside or outside of the ice with a relatively low velocity before the critical length is reached, and then at a much higher velocity. Moreover,
The main objective of the present study is to further our understanding of the influence of ambie... more The main objective of the present study is to further our understanding of the influence of ambient temperature, freezing water conductivity and nature of applied voltage on the surface flashover of ice. Flashover tests were carried out using two metallic hemispherical capped rods 12 mm in diameter, separated by an ice surface. The distance between the electrodes was 18 mm. Ice surface flashover voltage was determined under alternating, DC-positive and DC-negative voltages using a method based on 50% withstand voltage. The results obtained show that flashover voltage on ice surfaces decreases with an increase in ambient temperature and freezing water conductivity. Moreover, flashover voltage depends on the nature of the applied voltage. q 1998 Elsevier Science B.V.
2009 IEEE Conference on Electrical Insulation and Dielectric Phenomena, 2009
Positive dc arc propagation on an ice surface was studied by high speed photography and simultane... more Positive dc arc propagation on an ice surface was studied by high speed photography and simultaneous measurement of leakage current and voltage. All experiments were performed on a 120-cm long simplified physical model simulating real ice-covered insulators. Some features of the arc development pattern like minor and major arc collapses and the effects of arc propagation direction were examined. Previous
A laboratory study of ice accretion from supercooled droplets on energized insulators was investi... more A laboratory study of ice accretion from supercooled droplets on energized insulators was investigated. Wet ice, which is associated with the highest probability of flashover, was produced at temperatures of _12°C and _7°C with water droplets of 50 and 80 11m and liquid water contents of 4.4 and 6.8 g.m-3. Wind velocity and the conductivity of freezing water played important roles in the uniformity and roughness of ice accreted, respectively. It was also found that the mean power fed to the insulators by conduction current and corona discharges was about 40% of heat power liberated by the freezing process during wet ice accretion.
In today’s economic climate, it is important to know the condition, by means of suitable diagnost... more In today’s economic climate, it is important to know the condition, by means of suitable diagnostic tests, of the oil impregnated paper usable as primary insulation in equipment such as transformers, switchgear, bushings, cables and their accessories. The aim of this paper is regarded as a main task to study the parameters that mostly influence life time of Aramid paper built high voltage transformers. It is shown that the initial moisture content of Aramid paper as well as the metallic catalysts seem to have practically no influence on the aging process. The presence of oxygen however markedly increases the degradation rate.
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Papers by M. Farzaneh