Study on the Hydrophobicity of HTV SIR Treated by Different Corona Intensity
27 Mar 2009-pp 1-4
TL;DR: In this paper, the influence of corona intensity on the hydrophobicity of HTV SIR was investigated and the results showed that when the corona duration is shorter, the hydophobicity recovery quickens up with the increasing of the intensity.
Abstract: HTV SIR has been widely used as the outer insulation of composite insulators, which mainly depends on the unique hydrophobicity of HTV SIR. In this paper, the influence of corona intensity on the hydrophobicity of HTV SIR was investigated. The HTV SIR samples were aged under five levels of voltage. The hydrophobicity loss and recovery were evaluated by static contact angle. Experiments results show that the hydrophobicity won't lose until the corona intensity gets the corona onset electric field. Once the corona discharge occurs, the hydrophobicity loss will be accelerated with the enhancement of corona intensity. As for the hydrophobicity recovery, when the corona duration is shorter, the hydrophobicity recovery quickens up with the increasing of corona intensity. The hydrophbicity recovery, however, slows down by the enhancement of corona intensity when the corona duration is prolonged to a certain value. Meanwhile, it is noticed that under some aging condition, the hydrophobicity of HTV SIR can't get recovery even if the storage time is enough long. So it is assumed that there is no affirmatory correlation between the hydrophobicity recovery speed and the corona intensity. Further analysis identify that the microstructure and chemical composition play an important role in the hydrophobicity recovery progress.
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TL;DR: In this article, the effect of micro and/or nano fillers in silicone rubber composites in suppressing the damage of AC corona discharges was investigated using phase-resolved partial discharge (PD), hydrophobicity loss-recovery, Scanning Electron Microscopy (SEM), surface roughness and Fourier Transform Infrared Spectroscopy (FTIR).
Abstract: Outdoor insulators are often subject to corona discharges and the problem is becoming more prevalent with the increasing use of higher transmission voltage levels. For polymeric insulators, exposure to such discharges can alter the chemical structure of basic polymer and degrade surface properties. This paper investigates the effect of micro and/or nano fillers in silicone rubber composites in suppressing such damage. Four different types of samples are fabricated: pristine silicone rubber (PR), 30wt% micron–sized silica/silicone rubber (MC), 27.5wt% micron + 2.5wt% nano silica/silicone rubber (NMC), and 5wt% nano silica/silicone rubber (NC) composites. Samples are exposed to AC corona using a needle to ground-plane electrode setup. Experimental results are analyzed based on five different measurement methods: phase-resolved partial discharge (PD), hydrophobicity loss-recovery, Scanning Electron Microscopy (SEM), Surface roughness and Fourier Transform Infrared Spectroscopy (FTIR). Results indicate that NC shows a strong resistance to partial discharges and hydrophobicity loss. In the area below the needle tip, higher hydrophobicity loss and higher recovery are observed as compared to the vicinity region. Variations in surface roughness, appearance of crackles, voids, pits, surface splitting into blocky structures and damages to chemical structure of silicone rubber are appreciably retarded in NC as compared to PR, MC and NMC. Based on NMC results, it is found that addition of nano–sized silica can be an attractive approach to improve the corona resistance of micron–sized silica filled silicone rubber.
62 citations
Cites background from "Study on the Hydrophobicity of HTV ..."
...The problem of corona partial discharge (PD) is becoming more common in view of increasing trend in UHV transmission lines [13-15]....
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01 Aug 2014
TL;DR: In this paper, nano-silica with size of ∼20nm is used as filler to reduce the surface hydrophobic characteristics of silicone rubber (SR) nanocomposites at low pressure of 60kPa.
Abstract: During service, corona discharge could arise on outdoor composite insulators under wet conditions and its intensity can be accelerated at high altitude due to low air pressure. This phenomenon reduces the surface hydrophobic characteristics. In this paper, AC corona aging studies are carried out on silicone rubber (SR) nanocomposites at low pressure of 60kPa. Nano-silica with size of ∼20nm is used as filler. SR nanocomposites with different loading by weight are prepared by using mechanical stirrer and ultrasonic water bath techniques. For the creation of AC corona discharge, a point to plane electrode configuration is used in a glass chamber and its internal ambient pressure is decreased to 60kPa using vacuum pump to simulate high altitude condition. The specimens are sandwiched between the electrodes, in direct contact with the plane electrode (ground) but separate from the point electrode by a fixed air gap. The specimen surfaces are exposed to continuous corona discharge from the point electrode for extended periods. Results of accelerated corona aging test at 60kPa indicate that corona resistance of SR is remarkably improved by dispersing nano-silica in base matrix at 5wt% loading. After 48 hours of continuous corona exposure, loss in hydrophobicity is reduced by 18" and the formation of cracks on surface is significantly suppressed in the 5wt% sample. It is also perceived that absorption peak heights of Si-O-Si and Si-CH 3 in 5wt% aged sample are less decreased by 4% and 12.5%, respectively as compared to unfilled aged SR sample.
17 citations
TL;DR: Results showed that the TSC test was comprehensively embodied the corona aging characteristics caused by physical and chemical defects, and results of TSC tests could be selected as an effective criterion for aging evaluations.
Abstract: To study effects of pressure, humidity and aging time on the corona aging process, aging characteristics of silicone rubber composite insulators were researched by orthogonal tests. The test platform of adjustable pressure and humidity was constructed. TSC, SEM and FTIR tests were selected for aged samples. By the range analysis, it showed that the effect of pressure on trapped charges was related to humidity and aging time. There were more trapped charges when the humidity was higher, and the influence of humidity was more obvious along with the longer aging time at a low pressure. As the pressure increased, however, the effect of humidity on trapped charges was gradually reduced. But the influence of aging time was more significant, while aged degree of silicone rubber was deepened with increasing aging time. Furthermore, the aging state of materials was the collaboration effect of charged particles and nitric acid. Moreover, it could be seen from TSC, SEM and FTIR tests, sorting results of aging states were inconsistent. Results showed that the TSC test was comprehensively embodied the corona aging characteristics caused by physical and chemical defects. Therefore, results of TSC tests could be selected as an effective criterion for aging evaluations.
5 citations
01 Jan 2013
TL;DR: The PFISTERER SEFAG AG has more than thirty years of experience in processing low viscosity silicone rubber such as room temperature vulcanising (RTV) rubber and liquid silicone rubber (LSR) as well as high viscosity solid silicone rubber as discussed by the authors.
Abstract: This chapter reports on the latest materials and production processes used in the manufacture of composite insulators It also looks back at the development of rod materials as well as experiences relating to the in-house manufacture of glass-fibre reinforced semi-finished parts PFISTERER SEFAG AG has more than thirty years of experience in processing low viscosity silicone rubber (namely room temperature vulcanising (RTV) rubber and, more recently, liquid silicone rubber (LSR) as well as high viscosity solid silicone rubber (namely high temperature vulcanising (HTV) rubber) Given this level of experience and silicone rubber’s acknowledged importance as a reliable housing material, this chapter will focus on providing a detailed account of this group of materials As a result of the close interaction between material formulations, applicable manufacturing processes and operation-relevant properties, the results of key material analyses will also be presented here
4 citations
01 Jan 2013
TL;DR: In this article, the authors consider the problem of water droplet corona discharge on composite insulators and propose some simple mostly empirical rules to prevent the occurrence of corona discharges.
Abstract: Partial discharges on the surface of a composite insulator, known as surface partial discharges, are particularly significant because their energy input resulting from an impact and/or heat may damage the solid insulating materials. Whereas air molecules can regenerate themselves, damage to the solid surface is usually permanent and leads to cumulative damage (surface ageing), which may cause the insulation system to fail (fracture, flashover, etc.). Since the term “corona” has been retained in the context of overhead transmission lines, it will also be used here. By the application of some simple mostly empirical rules, it is possible to prevent the occurrence of corona discharges on composite insulator string or sets. Current standards for conventional insulator sets do not differentiate between conventional and composite insulators and are applicable insofar as the occurrence of a continuous corona at hardware components or at the insulator end fitting can be tested directly. The phenomenon of water droplet corona, which depends on numerous factors, should be given special consideration in the case of hydrophobic composite insulators. The composite insulator design (i.e. the material chosen, the stability of the sealing system, etc.) and the stresses that occurs at the service location can play a significant role here. The threshold value 4.5 kV/cm is defined as empirical value and can be regarded as a conservative recommendation, especially in view of the current trend whereby cost pressures are resulting in further developments with a lower fault tolerance. High-grade insulating materials ensure safe operation even when the threshold value for water droplet corona is exceeded. However, this does not apply to insulator sets that are subjected to a continuous corona discharge. Even if acid-resistant (E-CR) glass is used in this scenario, there may be some cumulative damage, which will ultimately cause the composite insulator to fail.
3 citations
References
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TL;DR: In this paper, contact angle measurements of a high-temperature-vulcanized polydimethylsiloxane (PDMS) elastomer have been obtained for different periods of time in dry air.
406 citations
TL;DR: In this article, a critical evaluation of the chemical and physical mechanisms responsible for hydrophobicity loss and recovery is presented, where the authors evaluate the properties of silicone rubbers based on polydimethylsiloxane (PDMS).
Abstract: Water repellency, high surface resistivity, vandalism resistance, low density and good processability have made silicone rubbers based on polydimethylsiloxane (PDMS) very attractive materials in housings for outdoor insulation. Their ability to recover hydrophobicity after oxida. tion or contamination is of paramount importance and this is the topic of this review. A critical evaluation of the chemical and physical mechanisms responsible for hydrophobicity loss and recovery is presented.
318 citations
"Study on the Hydrophobicity of HTV ..." refers background or methods in this paper
...Contact angle measurement is the ideal method to characterize surface hydrophobicity and is probably the most used technique in studies of loss and recovery of hydrophobicity of SIR[ 2 ]....
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...In was kept at 20r 5% and the temperature was just at room general, the hydrophobicity recovery will ensue after a temperature. subsequent period of rest[ 2 ]....
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TL;DR: In this paper, the authors reviewed the unique properties of polydimethylsiloxane (PDMS) elastomers that make it suitable for HV applications and suggested that diffusion of low molecular weight PDMS components is the more important mechanism of hydrophobic recovery.
Abstract: Most of the silicone materials used for Hv outdoor insulation are high-consistency, heat cured polydimethylsiloxane (PDMS) elastomers. The unique properties of PDMS that make it suitable for HV applications are reviewed. The surface of these elastomers can be rendered hydrophilic by exposure to discharges. A time and temperature dependent hydrophobic recovery ensues when exposure ceases. A variety of surface characterization investigations have established that corona exposure forms a brittle, wettable, silica-like layer on the surface of most PDMS elastomers. This is consistent with similar effects from oxygen and inert gas plasma treatment. There is still considerable debate as to the relative importance of the two major mechanisms postulated to account for the hydrophobic recovery after corona discharge. The diffusion mechanism invokes migration of low molecular weight species from the interior to the surface, while the reorientation or overturn mechanism envisages a surface reorganization with polar entities such as silanol groups resulting from surface oxidation rotating away and being replaced by methyl groups in the outermost surface layers. In our view, the highly crosslinked silicalike layer cannot reorient readily between hydrophilic and hydrophobic states at the surface, suggesting that diffusion of low molecular weight PDMS components is the more important mechanism of hydrophobic recovery. Recent data obtained on PDMS samples free from lowmolecular- weight diffusible species show that hydrophobic recovey may be due to in-situ depolymerization.
171 citations
TL;DR: In this article, a survey of the properties of silicone rubber for outdoor insulation is presented and the methods of assessing these properties are discussed and this is followed by a detailed survey of what is known of aging recovery mechanisms.
Abstract: This paper surveys the properties which give silicone rubber its distinctive and highly desirable performance characteristics for use as outdoor insulation. The methods of assessing these properties arediscussed and this is followed byadetailedsurveyof whatis knownof agingaud recovery mechanisms. Corona is identified as the principle electrical aging agent and evidence is presented for irreversible loss of polymer as a result of aging. However, the surface recov. ery mechanisms are robust and, provided there is an adequate resting period, the hydrophobic properties recover, This supports the view, from service experience, that there is no substantial evidence to show that normal aging, unless it results in the exposure of the glass fiber core, detracts from the performance of insulators.
150 citations
"Study on the Hydrophobicity of HTV ..." refers methods in this paper
...Abstract—HTV SIR has been widely used as the outer insulation aging mode for composite insulators[7]....
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TL;DR: The influence of long-term corona on the degradation of non-ceramic composite insulator (NCI) housing materials was studied in this article, where the effect of relative humidity and externally applied mechanical stress as acceleration factors was assessed.
Abstract: The influence of long-term corona on the degradation of non-ceramic composite insulator (NCI) housing materials was studied. Polymer samples were obtained from full-scale NCI, employing three different housing materials, namely silicone rubber, ethylene propylene diene monomer rubber and a blend of EPDM with silicone rubber. The effect of relative humidity and externally applied mechanical stress as acceleration factors was assessed. Several modes of degradation were observed, namely, cracking, roughening, and discoloration. In general the severity of degradation increased with the relative humidity level and application of mechanical stress. Periodic monitoring of corona discharge magnitude and pulse repetition rate allowed for a simplistic computation of the energy needed for initiation of surface changes. A comparison of these calculated values with expected conditions in the field was made, It is postulated that even under severe operating conditions over a period of many years, degradation of the housing materials evaluated due to water droplet corona is highly unlikely.
132 citations
"Study on the Hydrophobicity of HTV ..." refers background in this paper
...measurement. Especially with the growth of ultra high voltage grid, the In order to make it convenient to analyze the succeeded corona discharge becomes very common in field[ 4-6 ]....
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