Corona discharge phenomenon and behavior of water droplets on the surface of polymer in the AC electric field
01 Jun 2003-Vol. 2, pp 638-641
TL;DR: In this article, the behavior of water droplets on the polymer surface in an increasing ac electric field and corona discharge phenomenon during this process was examined by placing water droplet with different conductivities and volumes on the silicone rubber surface with a micropipette, which can be observed that the droplet vibrates and elongates with being pulled towards the positive electrode in wave synchronism with the frequency of the power source.
Abstract: This paper describes the results of experiments made to examine behavior of water droplets on the polymer surface in an increasing ac electric field and corona discharge phenomenon during this process Tests were done by placing water droplets with different conductivities and volumes on the silicone rubber surface with a micropipette The factors that affect the corona discharge from water droplets were analyzed by means of electric field calculation and some experiments It is demonstrated that water droplets on the polymer surface locally enhance the electric field and may cause corona discharge Behavior of water droplet, corona discharge current pulses and the light emission images were investigated with a digital oscilloscope and a high-speed camera It can be observed that the droplet vibrates and elongates with being pulled towards the positive electrode in a wave synchronism with the frequency of the power source The volume and conductivity of water droplet are shown to have a marked effect on the mode of corona discharge development
Citations
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TL;DR: In this paper, the authors present a review discussing methods of determination the resistance to corona discharges and ozone of polymeric materials for applications in outdoor insulation and describe a part of international activities within CIGRE WG D1.01 aiming to develop suitable methodology for the testing, which includes designing the necessary test arrangement, defining test conditions and finally exemplifying results of the treatment by monitoring changes of electrical, mechanical and structural properties of some materials.
Abstract: This paper presents a review discussing methods of determination the resistance to corona discharges and ozone of polymeric materials for applications in outdoor insulation. It also describes a part of international activities within CIGRE WG D1.01 aiming to develop suitable methodology for the testing, which includes designing the necessary test arrangement, defining test conditions and finally exemplifying results of the treatment by monitoring changes of electrical, mechanical and structural properties of some materials.
63Â citations
TL;DR: In this paper, the authors consider discharges between water drops when a limited alternating current is available, as experienced by an ageing insulator in service, and identify a phenomenon in which the length of a discharge between two drops is reduced through a particular type of distortion of the drops.
Abstract: Discharges between water drops are important in the ageing of hydrophobic outdoor insulators. They may also be important in the processes leading up to flashover of these insulators in high pollution conditions. This paper considers discharges between drops when a limited alternating current is available, as experienced by an ageing insulator in service. A phenomenon is identified in which the length of a discharge between two drops is reduced through a particular type of distortion of the drops. This is visually characterized as a liquid protrusion from each of a pair of water drops along the insulator surface. This process is distinct from vibration of the drops, general distortion of their shape and the very fast emission of jet streams seen in very high fields. The process depends upon the discharge current, the resistivity of the moisture and the hydrophobicity of the insulation surface.
47Â citations
Cites background from "Corona discharge phenomenon and beh..."
...Zhu et al [27] previously showed corona onset for a single drop of water decreases with conductivity....
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TL;DR: In this article, the waveform of leakage current flowing through the surface of HTV (high temperature vulcanized) silicone rubber specimen exposed to clean fog was examined and a dynamic 3D model was built to calculate the electric field and current density distribution on the specimen surface by a finite element software.
Abstract: This paper describes the results of experiments and simulations made to examine the waveform of leakage current flowing through the surface of HTV (high temperature vulcanized) silicone rubber specimen exposed to clean fog. Water droplets were placed on the surface of specimen energized with AC voltage and investigations of the surface state were done by a high-speed video camera in a wet condition produced by sprayed clean fog. Simultaneously, according to the experimental condition, a dynamic 3-D model was built to calculate the electric field and current density distribution on the specimen surface by a finite element software. A conducting water layer is formed due to the deformation of droplets and the development of dry band arcing. This caused large distortion and nonlinearly which increased the odd harmonic components in the leakage current waveform. This is in good agreement with the simulating calculation. The information from the leakage current frequency characteristic was extracted and correlated with the insulation surface condition. It can be considered as a diagnostic index for electrical characteristics and insulation state of polymer insulators in the wet condition.
34Â citations
TL;DR: In this article, the authors investigated the corona inception and its relation with polymer surface conditions and showed that certain service conditions, particularly the association water droplets and pollution, enhance the electric field and can lead to corona onset.
Abstract: Concerns about corona and its harmful effects, particularly in polymer insulators, have increased in recent years. Research involving corona identification, quantification, and formation mechanism is important to understand the aging process and to avoid premature failures. This paper investigates the corona inception and its relation with polymer surface conditions. Experiments of visual corona identification and Radio Interference Voltage (RIV) measurements were performed. Corona onset voltage was investigated in arrangements simulating different service conditions. Wet and contaminated insulating surfaces were reproduced. An RTV coated insulating sample and a polymer insulator were used. The electric field (E-field) at corona onset was numerically evaluated through computational simulations using the Finite Element Method. Corona onset voltage, E-field and RIV were analyzed according to the contamination level. The results clearly show how certain service conditions, particularly the association water droplets and pollution, enhance the E-field and can lead to corona onset.
31Â citations
TL;DR: In this article, the effect of different types of water droplets arrangements, their position and dry bands width on the flashover voltage of the silicone insulating surface with non-uniform electric field systems was quantified.
23Â citations
References
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TL;DR: In this paper, the authors present a review of the recent performance experience of HV composite polymeric insulators in outdoor service, testing methods, aging, the ranking of the materials, the role of fillers, low molecular weight components present in the insulators, mechanisms responsible for the loss and recovery of hydrophobicity, one of the most important properties of polymers, the mechanisms of failure, detection of faults, type and quantity of natural contaminants, effects of exposure to rain, hydrocarbons, stationary air and wind, various methods to optimize the electrical performance and a
Abstract: HV composite polymeric insulators are being accepted increasingly for use in outdoor installations by the traditionally cautious electric power utilities worldwide. They currently represent -60 to 70% of newly installed HV insulators in Nortb America. The tremendous growth in the applications of non-ceramic composite insulators is due to their advantages over the traditional ceramic and glass insulators. These include light weight, higher mechanical strength to weight ratio, resistance to vandalism, better performance in the presence of heavy pollution in wet conditions, and comparable or better withstand voltage than porcelain or glass insulators. However, because polymeric insulators are relatively new, the expected lifetime and their long-term reliability are not known and therefore are of concern to users. Additionally they might suffer from erosion and tracking in the presence of severe contamination and sustained moisture. This leads to the development of dry band arcing that under certain circumstances could lead to failure of polymer insulators. In this paper a review is presented of the recent performance experience of HV composite polymeric insulators in outdoor service, testing methods, aging, the ranking of the materials, the role of fillers, the role of low molecular weight components present in the insulators, the mechanisms responsible for the loss and recovery of hydrophobicity, one of the most important properties of polymers, the mechanisms of failure, detection of faults, type and quantity of natural contaminants, effects of exposure to rain, hydrocarbons, stationary air and wind, various methods to optimize the electrical performance and a relatively new method for evaluating the performance status of polymeric insulators in the field.
495Â citations
TL;DR: In this article, the fundamental principles of water drop corona as an aging mechanism for nonceramic insulators are presented, and it is demonstrated that water drops in the shed and sheath regions enhance the electric field and may cause corona which can play an important role in long-term performance.
Abstract: The fundamental principles of water drop corona as an aging mechanism for nonceramic insulators are presented. It is demonstrated that water drops in the sheath regions enhance the electric field and may cause corona which can play an important role in long-term performance. Electric field enhancement caused by water drops in different locations on the shed and sheath are demonstrated by means of electric field calculations and small scale experiments. The threshold magnitude of the surface electric field for corona from water drops is presented for two silicone rubber surfaces having different hydrophobic properties. The effect of water drop corona activity on the properties of the surface material is shown using small scale aging experiments.
181Â citations
TL;DR: In this article, it was shown that certain regions of commercially available 500 kV non-ceramic insulators have surface electric fields that are above the threshold for water drop corona.
Abstract: It is shown that certain regions of commercially available 500 kV non-ceramic insulators have surface electric fields that are above the threshold for water drop corona. Observations made in a full scale accelerated aging chamber, and in service, demonstrate that water drop corona occurs on such insulators. A correlation between the magnitude of the surface electric fields and the condition of the silicone rubber non-ceramic insulator surfaces due to water drop corona is illustrated for two different insulator types in an accelerated aging chamber. Other examples of degradation of nonceramic insulators due to water drop corona are illustrated.
118Â citations
TL;DR: In this article, measurements of partial discharge (PD) from water droplets on a silicone rubber insulating surface in an ac field were performed by using a micro-pipette, and by condensing water in a controlled humidity chamber.
Abstract: This paper presents measurements of partial discharge (PD) from water droplets on a silicone rubber insulating surface in an ac field. Tests are done by placing droplets on the surface using a micro-pipette, and by condensing water in a controlled humidity chamber. The field enhancement factor due to droplets placed on the insulation surface is experimentally and numerically determined. Values in the range of 3.8 to 6.3 are obtained depending on the size and number of droplets. The time resolved analysis of PD from water condensation indicates a threshold field, between 3.0 and 3.5 kV/cm, above which the PD activity increases with time, and brings the insulation to a surface breakdown. The corresponding field enhancement factor obtained for the condensation experiments is between 5.8 and 6.8. The results therefore suggest that the PD activity on the hydrophobic surface can be used effectively to learn about the insulation surface conditions.
105Â citations
"Corona discharge phenomenon and beh..." refers background or result in this paper
...But just because of its good hydrophobicity, waiter droplets will be formed on the surface of polymer exposed to rain and moisture, and hence the conductive coritamination dissolved within the water is discontinuous [ 2 ]....
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...Under partially wet conditions, the electric field distribution is much more complex to computer [ 2 ], but the simple simulating field calculation results described above are in a reasonable agreement with the experimental results....
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...( 2 ) The electric field at the triple junction is obviously intensified due to the difference in the permittivity of silicone rubber, air and water droplet....
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...Figure 2 Calculated electric field distribution on the silicone rubber surface...
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...Water droplets with the conductivities of 2 .0pS/cm (ion-exchange water), 800pSkm (salt water) and 20mS/cm (solution simulated as sea water), whose volumes were respectively about 30~1, 50~1 and 100~1,...
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14 Oct 2001
TL;DR: In this article, a high speed video camera was used to examine the nature of discharge phenomena between water drops on polymer surfaces and found that the shape of water drops change to shape more likely to intensify the electric field around them and initiate discharges at the solid/liquid/gas interface.
Abstract: This paper describes the results of experiments made to examine the nature of discharge phenomena between water drops on polymer surfaces. Small samples of high temperature vulcanised silicone rubber were subjected to electric stress and exposed to clean and salt fog. The resulting surface activity was observed with a high-speed video camera. Water drops on the surface were found to vibrate in a variety of ways and were pushed away from the high electric stress regions to low stress regions. The distribution of the water drops on the surface of the samples appeared to follow equipotential lines between the electrodes. Water drops on the surface grew larger by absorbing droplets from the fog or by coalescing together. Depending on the size of water drops, the process of water drop coalescence took up to several cycles of the 50 Hz supply voltage. During this period the shape of water drops was observed to change to shapes more likely to intensify the electric field around them and thus initiate discharges at the solid/liquid/gas interface. When several water drops simultaneously coalesce, they can bridge substantial lengths of insulation and there may be an increased risk of flashover. The conductivity of the fog is shown to have A marked effect on the mode of discharge development. Salt crystals deposited on the surface by salt fogs greatly increase the conductivity of water drops during drying and wetting of the polymer surface.
40Â citations