Article

Field and laboratory aging of RTV silicone insulator coatings

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The silicone-based coating applied to 345 kV post insulators in a substation on the shore of Long Island Sound has depolymerized over a period of about 7 years although no in-service failures have occurred. However, the increasing rate of depolymerization suggests that the coatings will have to be renewed in the near future. This paper reports comparisons of aging and material properties for a number of RTV silicone insulator coatings and measurements related to application of a new coating over an existing, field-aged coating

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... RTV and HTV materials are composed of at least 30 wt % of polydimethylsiloxane (PDMS) [1,2]. NCI HTV insulator SIRs are mixtures of PDMS and of several additives such as fire retardants, fungicides, and fillers to increase stiffness and color [1][2][3][4][5][6][7][8][9][10][11][12]35]. These additives are compounded into the SIR, along with alumina trihydrate, which is the primary fire retardant in NCIs [36]. ...
... SIRs provide the necessary surface hydrophobicity for NCIs, preventing standing water, as rainwater and atmospheric condensation beads on the SIR surface due to its low-energy surface, preventing water ingress [1][2][3][4][5][6][7][8][9][10][11][12]. Excess water on NCI surfaces can cause leakage currents, which can form an electrical path to ground resulting in a local black out or worse [7][8][9][10][11][12]. ...
... SIRs provide the necessary surface hydrophobicity for NCIs, preventing standing water, as rainwater and atmospheric condensation beads on the SIR surface due to its low-energy surface, preventing water ingress [1][2][3][4][5][6][7][8][9][10][11][12]. Excess water on NCI surfaces can cause leakage currents, which can form an electrical path to ground resulting in a local black out or worse [7][8][9][10][11][12]. Oxidative stressors, such as UV and acidic rain, can damage SIRs, decreasing their hydrophobicity [2][3][4][5][6][7][8][9][10][11][12]. ...
Article
Full-text available
Silicone rubbers (SIRs) are common industrial materials which are often used for electrical insulation including weather sheds on non-ceramic insulators (NCIs). While SIRs are typically resilient to outside environments, aging can damage SIRs' favorable properties such as hydrophobicity and electrical resistance. Detecting SIR aging and damage, however, can be difficult, especially in service. In this study we used hyperspectral imaging (HSI) and previously investigated aging methods as a proof of concept to show how HSI may be used to detect various types of aging damage in different SIR materials. The spectral signature changes in four different SIRs subjected to four different in-service aging environments all occurred between 400--650 nm. Therefore, remote sensing of NCIs using HSI could concentrate on bands below 700 nm to successfully detect in service SIR damage.
... Acid rain can deteriorate high voltage outdoor insulators and affect their performance in addition to their other surface degrading effects1234. Polymeric insulators can especially be susceptible since they are mostly organic56. ...
... It is of practical interest to study the aging and degradation characteristics of commercially available polymeric insulators under acid rain + multistress conditions, simulating an actual service environment. Presented in this paper are the results of the studies on the effect of acid rain (pH 3.9) in the Connecticut area, USA [1] and at Taxila, Pakistan. Connecticut was chosen as failure of polymeric coating, Room Temperature Vulcanized (RTV) silicone rubber was observed within 6 years of in service performance in service under extra high voltage of 345kV [1, 7]. ...
... Presented in this paper are the results of the studies on the effect of acid rain (pH 3.9) in the Connecticut area, USA [1] and at Taxila, Pakistan. Connecticut was chosen as failure of polymeric coating, Room Temperature Vulcanized (RTV) silicone rubber was observed within 6 years of in service performance in service under extra high voltage of 345kV [1, 7]. It is of practical interest to study the performance of High Temperature Vulcanized (HTV) silicone rubber (SiR) insulators in this environment at a lower voltage as distribution class insulators are more commonly used. ...
Article
Full-text available
Polymers are becoming the material of choice for high voltage outdoor insulators. However being mostly organic, they are susceptible to aging and degradation (weathering) due to environmental (and electrical) stresses. This necessitates the study of their long-term behavior. It is desirable to study the long-term performance of the insulators in the service environment under multistress conditions encountered by the insulators to better simulate the actual conditions. This paper presents the results of the studies of a novel, third generation, environmental friendly thermoplastic elastomeric (TPE) insulators and conventional thermoset silicone rubber (SiR) insulators in Connecticut, USA and Taxila, Pakistan. 28 and 10kV insulators were used for this purpose. The aging phenomena were characterized by visual observations, hydrophobicity classification and using sophisticated materials analysis techniques, such as FTIR. The results indicated that the TPE insulators had discoloration and arcing after two thousand hours of aging while the silicone rubber insulators had no arcing. Index Terms—multistress aging, acid rain, polymeric insulators
... The effects of acid rain have been recorded in parts of the United States, Germany, Netherlands, Switzerland and Australia. It is also becoming a significant problem in Japan, China and in Southeast Asia [1][2][3][4][5]. The definition of acid rain is not very clear, but generally rainwater with a pH below 5.6 is called acid rain and the main acids in the rain are sulfuric and nitric acids [4]. ...
... The degradation of polymeric materials in acid rain is an electrochemical process of de-polymerization that is more severe in the presence of voltage [2][3][4][5][6][7][8][9][10][11][12]. ...
... The inclined plane test, salt fog test, tracking wheel and voltage breakdown are some of the commonly used test methods to evaluate the aged polymeric insulators and coatings. Parameters like the leakage current, contact angle, SEM, TGA, FTIR, WAXD, gas chromatography, mass spectrometry and tan 6 have been used in analyzing results of aging [2][3][4][5][6][7][8][9][10][11][12]. But, the most common method for simulation of acidic aging is soaking of the coated samples in acid [4][5][6][7][8][9][10]. ...
Conference Paper
The paper presents the results of an investigation into the effect of acid immersion on the aging of room temperature vulcanized (RTV) silicone rubber coatings in inclined plane tests (IPT). Two commercial coatings, RTV-A filled with ATH (aluminum tri-hydrate) and RTV-B filled with silica, are compared before and after acid immersion. Acid aging consists of immersing the samples in 3.9 pH nitric acid at a temperature of 90°C for 2 weeks. The relative comparison between the two samples is based on the development of the fundamental and third harmonic of the leakage current during IPT tests, eroded area, the time to failure and SEM microphotographs. All of these observations show that acid rain damages RTV-A more severely than RTV-B. However virgin ATH filled sample showed a better performance compared to the silica filled material.
... A comprehensive study of the performance characteristics of four commercial RTV silicone rubber coatings for high voltage insulators has shown considerable variation in the aging characteristics of the coatings affecting life [5]. A material characterization technique like gas chromatography (GC) of the surface has provided evidence of depletion of LMW silicone fluid that diffuses from the bulk of the coating Manuscript received on 6 July 2013, in final form 13 September 2013, accepted 26 September 2013 to the surface [5,6]. This fluid acts to impart non-wetting characteristics to deposited contaminants by surrounding the particles with a monolayer of fluid. ...
... Moreover, the loss of hydrophobicity was correlated with oxidation in the coating surface revealed by significant change in the atomic concentration of oxygen and carbon measured by electron spectroscopy for chemical analysis (ESCA) [20]. Thermal gravimetric analysis (TGA) has shown significant difference between aged and virgin samples of RTV coating samples [6]. The TGA curve for the aged sample have lower peak around the 200-300 o C than the virgin sample which is an indication of the decomposition in the hydroxyl group in the Al 2 (OH) 3 . ...
Article
The paper provides several methods to assess the condition of RTV coated porcelain/toughened glass insulators in the field. Visual observations of arcing and audible corona are the first indications that signal changes to the coating have taken place. It emphasizes that in the absence of reliable data one can use observations based on hydrophobicity to evaluate when maintenance or replacement of the coated insulators is necessary. Life extension strategies are suggested. It also demonstrates that there are differences in the hydrophobicity characteristics among commercially available coatings, and these can be quantified using standard laboratory techniques. Field experience suggests that the life of the RTV coatings can exceed 10 years even under the severest conditions of pollution.
... There have been many studies on the engineering applications of silicone rubber coating in electrical power systems, which have provided many theoretical bases for the engineering applications of silicone rubber coatings [2][3][4][5][6][7][8][9][10]. However, research on the characteristics of the partial discharge on the surfaces of silicone rubber coatings is rare. ...
Article
Full-text available
A pollution flashover along an insulation surface—a catastrophic accident in electrical power system—threatens the safe and reliable operation of a power grid. Silicone rubber coatings are applied to the surfaces of other insulation materials in order to improve the pollution flashover voltage of the insulation structure. It is generally believed that the hydrophobicity of the silicone rubber coating is key to blocking the physical process of pollution flashover, which prevents the formation of continuously wet pollution areas. However, it is unclear whether silicone rubber coating can suppress the generation of pre-discharges such as corona discharge and streamer discharge. In this research, the influence of silicone rubber coating on the characteristics of surface streamer discharge was researched in-depth. The streamer ‘stability’ propagation fields of the polymer are lower than that of the polymer with silicone rubber coating. The velocities of the streamer propagation along the polymer are higher than those along the polymer with silicone rubber coating. This indicates that the surface properties of the polymer with the silicone rubber coating are less favorable for streamer propagation than those of the polymer.
... In the process of long-term operation, a series of deterioration phenomena such as mechanical and electrical performance degradation of composite insulators generally occur, which leads to the shortening of service life. Serious aging composite insulators may even lead to transmission line external insulation flashover, broken string, wire landing and other malignant accidents [11][12]. The long-term performance of composite insulator is studied systematically [13][14][15][16]. ...
Article
In order to improve the outdoor service life of composite insulators, the effect of electron beam irradiation on SIR is studied. In this paper, the silicone rubber was treated by two different doses of electron beam irradiation, and the accelerated aging test of 1000 h high temperature, high humidity and strong sunlight was carried out in the multi factor aging test chamber. At the same time, the physical and chemical properties such as physical tensile properties, hydrophobicity, optical microscope, scanning electron microscope (SEM), Attenuated Total internal Reflection Fourier Transform Infrared Spectrometer(ATR-FTIR) and crosslinking density were analyzed. The results showed that after low electron beam irradiation dose (40 kGy) treatment, the crosslinking density of silicone rubber increased by 8.8 times, and after 1000 h aging treatment, the crosslinking density of low irradiated(40 kGy) silicone rubber is still 6 times higher than that of unirradiated silicone rubber. Based on the analysis of the test results, the surface modification mechanism of silicone rubber under electron beam irradiation and aging is proposed. The research observation results demonstrate the influence of electron beam irradiation and aging on silicone rubber. Related research provides a novel idea for improving the service life of insulators.
... In the presence of water droplets and contamination layer, loss of hydrophobicity occurs which results in the formation of a conductive film on the surface [78,79]. The electrical discharges and dry band arcing occur on the insulator surface which produce a large amount of heat in the discharge area which causes the tracking and erosion on the surface of insulator and insulator may lose its dielectric property completely [80][81][82][83][84][85][86]. ...
Article
Full-text available
High-voltage direct current (HVDC) transmission is known as green-energy transfer technology and has recently become an attractive alternative of high-voltage alternating current (HVAC) due to its high-power transmission capability and lower power loss. Use of composite insulators on direct current (DC) transmission lines experienced rapid growth in recent years due to their high hydrophobicity and better performance in contaminated environment than conventional ceramic insulators. During their service operation on DC lines, insulators are prone to more accumulation of contaminants due to unidirectional electric field. The contaminants under wet conditions allow leakage current to flow on the insulator surface. Being organic in nature, polymeric insulators have a tendency to age under the combined effects of electrical and environmental stresses. To fully understand the long-term aging performance of DC composite insulators, a detailed survey was considered necessary. Towards that end, this paper critically summarizes worldwide experience of aging performance of composite insulators in the field as well as in laboratory conditions.
... Under adverse conditions, a certain level of chalking and shedding might occur in some local areas of the insulator surface, resulting in uneven distribution of hydrophobicity. As indicated in [19,20], the uneven distribution of hydrophobicity had a certain impact on the pollution flashover performance of RTV coated insulator. ...
Article
Under conditions of high temperature, high humidity, and strong ultraviolet radiation, RTV coating on the insulators may get aged, powdered and even peeled off. The physical damage of the RTV coating on the insulator surface can result in a reduction in the pollution flashover performance. Therefore, this study investigated the influence of location, lateral length, and longitudinal length of the damage on the pollution flashover voltage of RTV-coated insulators. From the experimental results, it was found that the longitudinal length of the damage along the creepage distance direction was the most influential factor on the pollution flashover voltage. According to the flashover voltage function obtained by fitting, the concept of “effective path” distance was proposed. This concept can be used to analyse the influence of multiple damages on the pollution flashover voltage. To validate the analysis, verification experiments were performed using typical industrial insulator. The results showed that the pollution flashover voltage of the insulator was also in a linear relationship with the proposed “effective path” distance, which confirmed the mechanism analysis.
... But when the contamination degree of insulators is serious, these insulators cannot completely prevent pollution flashover.Therefore, RTV coatings have been introduced and used as an improved method to prevent pollution flashover [1]- [3]. However, the influence of external environment will cause some damage to RTV coatings [4]- [10] and obviously affect the insulators' resistance to pollution flashover [11]- [14]. ...
Article
In recent years, RTV (Room Temperature Vulcanizing) coated insulators have been increasingly applied in transmission lines. A large number of RTV coating damages on insulators are currently found. In this paper, 3 typical damage modes of the RTV coating were simulated, then the pollution flashover characteristics were studied. Results indicated that there is a big difference between AC flashover performance of RTV coated insulators under different damage modes. The flashover voltage, as well as the critical leakage current, is largely influenced by salt deposit density (SDD), damage modes and damage area. The relationship between SDD and U50 still meets negative power function when RTV coating was damaged. Insulators with fan-shaped damage have lowest flashover voltage and greatest critical leakage current. Both 2D and 3D FEM models of RTV coating damaged insulator pollution layer were developed to calculate leakage current density on damaged surface, it is discovered that the starting position of the arc usually occurs where the current density is maximum. The different damage modes lead to the change of the surface pollution layer conductivity and the uneven distribution of the current density, which is the main reason that pollution flashover characteristics are directly related to the damage modes.
... On the other hand, when the insulator surface is contaminated, the RTV low molecule weight silicone fluid that diffuses from the bulk of the coating creates a monolayer of fluids (prevents the contaminant from dissolving in water) and imparts a non-wetting property/hydrophobicity to the contaminant layer. This results in the formation of a weak and non-conductive electrolyte layer, which is not conducive to the development of a leakage current or flashover [11][12]. ...
Article
Full-text available
Located near the equator, Malaysia is a country with one of the highest lightning densities in the world. Lightning contributes to 70% of the power outages in Malaysia and affects power equipment, automated network systems, causes data losses and monetary losses in the nation. Therefore, consideration of insulator evaluation under lightning impulses can be crucial to evaluate and attempt to overcome this issue. This paper presents a new approach to increase the electrical performance of polymer insulators using a Room Temperature Vulcanisation (RTV) coating. The evaluation involves three different settings of polymer insulator, namely uncoated, RTV type 1, and RTV type 2 upper surface coatings. All the insulators were tested under three different conditions as dry, clean wet and salty under different impulse polarities using the even-rising test method. The voltage breakdown for each test was recorded. From the experiment, it was found that the effectiveness of the RTV coating application became apparent when tested under salty or polluted conditions. It increased the voltage withstand capabilities of the polymer insulator up to 50% from the basic uncoated insulator. Under dry and clean conditions, the RTV coating provided just a slight increase of the breakdown voltage. The increase in voltage breakdown capability decreased the probability of surface discharge and dry band arcing that could cause degradation of the polymeric material housing. The RTV type 1 coating was found to be more effective when performing under a lightning impulse. The findings might help the utility companies improve the performance of their insulators in order to increase power system reliability.
... Room temperature vulcanized (RTV) silicone rubber with water repellency property (water contact angle greater than 90 • ) could prevent the surface from being completely wetted and owns antipollution ability resulting from migration of low molecular weight (LMW) silicon components from the bulk to the surface [6,7], which has been widely used in China, Canada and the United States for the past three decades [8][9][10]. However, considerable applications and studies [11][12][13][14] have indicated that hydrophobicity of RTV silicone rubber decreased with the increase of serving time. Moreover, the water droplet slide angle (SA) of RTV silicone rubber is pretty large (greater than 10 • ). ...
... Moreover, the loss of hydrophobicity was correlated with oxidation in the coating surface revealed by significant change in the atomic concentration of oxygen and carbon measured by electron spectroscopy for chemical analysis (ESCA) [5]. Thermal gravimetric analysis (TGA) has shown significant difference between aged and virgin samples of RTV coating samples [6]. The TGA curve for the aged samples have lower peak around the 200-300  C than the virgin sample which is an indication of the decomposition in the hydroxyl group in the AL(OH)3. ...
Conference Paper
Full-text available
In this paper, the characteristics of field-aged RTV silicone rubber coatings and silicone rubber insulators used in the gulf region were investigated. Samples were collected from both 220 and 400 kV field aged coated bushings and outdoor insulators. Samples taken from various positions on the insulators were analyzed using thermo gravimetric analysis (TGA). TGA analysis reveals that samples collected from 400 kV silicone rubber insulators showed signs of more aging compared to samples from 220 kV insulators. Also, for certain insulators, samples taken from the upper side of the sheds indicated higher degree of aging compared to samples taken from the same insulator but from the lower side of the sheds.
... It can be due to the decomposition of cyclic silicone oligomers and Si-C bonds of compositions which can be affected by UV radiation [1,20]. It has been found that 90 wt% of silicone rubber contains of cyclic dimethylsiloane (DMS) with 3 to 6 DMS units, and 1 wt% of linear DMS [1,[21][22][23][24]. Small units of silicone oligomers with 4 to 6 DMS units have low boiling temperatures from 173 °C to 245 °C. ...
Article
Full-text available
Ultraviolet (UV) aging is one of the most important problems that electrical insulations are faced with it. Generally, total UV radiation emitted from the sun is divided into three parts. Among all types of ultraviolet radiation, UVC has the highest energy because its wavelength is less than 290 nm. Therefore, UVC is definitely harmful for health and even for other objects on the earth including electrical insulators. The objective of the current paper is to study the aging process of silicone rubber insulators exposed to UVC radiation. To accomplish this purpose, three different kinds of commercial silicone rubber insulators were aged by UVC radiation and contaminated solution. Then their electrical and thermal properties as well as their changes on the surface were investigated by measuring leakage current, thermo-gravimetrical analysis and surface elements. It is observed that, the effect of contaminated solution on leakage current is more than the influence of UV radiation alone. In addition, combination of UVC radiation and pollution extremely increase leakage current. Pollution has especially influence on the 3th harmonic component. Aging by UVC shifts the thermal decomposition temperature of the insulations to lower temperatures and degrades the surface of the systems especially the polymers surround the filler. Also it was realized that UVC is able to decompose the filler and reduce the Al/Si ratio in the sample.
... Room Temperature Vulcanized (RTV) silicon rubber coatings are used in order to improve the contamination performance of outdoor high voltage insulators [1][2][3][4][5][6][7][8][9][10][11]. The improved performance of coated insulators is attributed to the hydrophobicity of the thin surface RTV coating film provided. ...
Conference Paper
Full-text available
Results on positive streamer propagation along smooth and profiled cylindrical insulating surfaces coated with different room temperature vulcanized (RTV) silicon rubber coatings are presented; nylon specimens were regarded as reference. Experiments were carried out in a three electrode arrangement consisting of a 12 cm long parallel-plane gap with an auxiliary needle in the earthed anode. Streamers were initiated by applying at the needle electrode a pulse voltage variable in amplitude and propagated over the insulators towards the upper plane electrode which was stressed by a negative DC voltage. When streamers propagate stably along an insulating smooth surface the propagation field and the associated velocity are both higher for RTV coated than bare insulators, however when they propagate along a profiled insulating surface with a step or a shed this reverses itself. The effect of a step or a shed on an insulating surface is to increase propagation field, with the only exception where a streamer crosses part of the gap in air alone, and to reduce the velocity of propagation at all applied fields. The increase of streamer propagation field due to surface profile is less marked for RTV coated than bare insulating surfaces whereas the reduction of propagation velocity is more pronounced.
... Additionally, it is impossible to generalize the experimental observations without clarifying the exact nature of the silicone studied and its physical state (prepolymer or crosslinked). In the framework of this study, the results obtained are consistent with the experimental data obtained by Homma et al. on both RTV and HTV silicones [47,48]. Using gas chromatography/mass spectrometry (GC-MS) technique, the authors clearly demonstrated that field aged silicones suffered from depolymerization and oxidation when they are used in HV equipments. ...
Article
The origin and the consequences of the electric failure of in-service composite hollow insulators used in railway transportation were investigated. Direct electrical measurements made it possible the detection of partial discharges (PD) and UV emissions allowed of identifying the location of the PD at the interface between metal braids and a silicone liner. To investigate the effects of the damaging PD activity, physicochemical properties of the different polymers were investigated and compared to new samples. The thermomechanical properties of the HTV and RTV silicones showed important alterations in the polymers structure. The chemical analyses of the silicones and nitrile rubber conducted using ATR-FTIR spectroscopy revealed that the polymers were oxidized after electrical failure. The results indicated that the ozone production and UV emission were due to the surface electrical activities. The breakdown of alumina trihydrate (ATH) in the inner HTV silicone liner demonstrated that undesired electrical discharges induced an significant increase of temperature and the formation of moisture in the air present in the hollow insulator. Laboratory artificial aging performed on the silicones and nitrile rubber showed similar degradation as in service. Further electrical experiments conducted on empty hollow insulators enabled the detection of internal PD located in micro-voids present in the adhesive used to bond the HTV silicone liner to the inner composite tube.
... For the reliability of the RTV 566 in the bond, its creep and aging behaviors have to be considered, and a predictable stress–strain behavior of the RTV 566 is desired. There are some literatures that discuss the aging phenomenon of RTV silicone rubber [3]–[5]. However, in these papers, the aging phenomenon had been discussed in " extreme environment, " i.e., corrosive, humid , or electric field. ...
Article
This paper reports the preliminary feasibility study of room temperature vulcanization (RTV) 566 for its application as a “spring” for in situ height adjustment in our proposed design for an array of Schottky emitters. The reliability of the RTV 566 is tested in terms of its viscoelastic properties for thicknesses of 95, 142, and 195 μm. The shear modulus varied a little with the thickness. Although the RTV 566 shows a very little hysteresis, it shows a clear sign of viscoelastic behavior, rendering it unsuitable for the application. The viscoelastic behavior of the RTV 566 is modeled with the Findley model.
Article
We live in an era of striking advancements in various domains of science and technology, where separate fields and specializations are overlapping into new horizons. This cooperative approach is emerging rapidly in polymer science by employing the organic and physical chemistry, materials science, as well as electrical and mechanical engineering to collaborate and develop uniquely innovative materials. In outdoor high voltage power equipment, various problems such as flashover, rain, icing, pollution, and UV can compromise the performance of insulators thereby distorting the reliability of the entire system. Superhydrophobic coatings are sought-after candidates owing to their ultra-non-wettable, easy-to-clean, and anti-ice character. However, the performance of superhydrophobic coatings when they are subjected to high-voltage fields is still lacking sufficient research. Here, we aimed at designing a robust and novel non-fluorinated superhydrophobic coating in order to increase the effective life-span of high-voltage insulators by preventing and/or delaying the possible arcing and flashover driven damages. The electrical properties of the coating were investigated through various and comprehensive test methods. The coating showed high thermal and desirable weathering stability. Compared with bare porcelain in dry, wet, and polluted conditions, the superhydrophobic coating successfully increased the flashover voltage. Moreover, the superhydrophobic coating exhibited low leakage currents through the condensation test when exposed to high humidity conditions. With leakage currents of as low as 20 mA after three continuous steps of voltage increase, the superhydrophobic coating showed less tracking and erosion lines than the pristine coating in an adapted inclined plane test for thin films.
Article
A lack of accepted standards and standardized phantoms suitable for the technical validation of biophotonic instrumentation hinders the reliability and reproducibility of its experimental outputs. In this Perspective, we discuss general criteria for the design of tissue-mimicking biophotonic phantoms, and use these criteria and state-of-the-art developments to critically review the literature on phantom materials and on the fabrication of phantoms. By focusing on representative examples of standardization in diffuse optical imaging and spectroscopy, fluorescence-guided surgery and photoacoustic imaging, we identify unmet needs in the development of phantoms and a set of criteria (leveraging characterization, collaboration, communication and commitment) for the standardization of biophotonic instrumentation. This Perspective overviews the design and fabrication of tissue-mimicking phantom materials for the technical validation of biophotonic instrumentation, and identifies a set of criteria for their standardization.
Article
The coatings have been in service for many years users are beginning to be concerned about the increased risk of flashover which are comes with aging, or the end-of-life, and the course of action that may be necessary for life extension or replacement. Study of the performance characteristics of commercial RTV silicone rubber coatings with various voltages.
Article
We have recently shown [1,2] that one component room temperature vulcanized (RTV-1) silicone rubbers (SIR) based on polydimethylsiloxane (PDMS) can be rapidly degraded by low voltage (LV) energized aqueous salt solutions by previously unreported aging mechanisms related to the formation of hypochlorous acid in high voltage (HV) transmission line applications. In this study, we are showing how to improve the resistance of the rubbers to extreme environmental aging by embedding TiO2 micro-particles. Molecular dynamics (MD) simulations were conducted to determine the combined effect of TiO2 and different concentrations of hydrophobic PDMS methyl groups on surface hydrophobicity of a TiO2/PDMS composite. In addition, the effects of both TiO2 and silica on the diffusivities of LV aqueous salt components in the PDMS were predicted and related to unique interfacial interactions between the particles and the methyl groups of the PDMS. Rutile TiO2 reoriented methyl groups away from the particles reducing the diffusivities of water and hypochlorous acid. This effect shielded the PDMS network against environmental chain scissions. On the other hand, silica attracted the groups accelerating acid and water migrations and thus enhancing damage to the network. In the experimental part, TiO2/RTV was subjected independently to hypochlorous acid and electrolyzed LV aqueous salt. As expected, TiO2 greatly increased the contact angle, reduced the surface energy and improved the hydrophobicity of the composite, mitigating the negative effect of the reduced concentrations of methyl groups. As a result, aging damage to the rubber was dramatically reduced by about 50% in highly oxidative environments.
Article
In this work we suggest an entirely new and highly transformative model of silicone rubber aging caused by the presence of electrolyzed aqueous salt, leading to the formation of hypochlorous acid in-service on energized High Voltage (HV) transmission lines in coastal environments. The model was subsequently verified by aging one-component Room Temperature Vulcanized (RTV-1) rubbers in commercially produced hypochlorous acid and an electrolyzed aqueous salt environment at room temperature. Molecular dynamics models of the rubbers with silica fillers were conducted to offer at least partial explanations of the types and extents of aging observed in the RTV-1 samples tested in the aqueous salt solutions. We have shown that the above environments are highly damaging to the silicone rubber polymer network and significantly more destructive than non-electrolyzed standard aqueous salt solutions at higher temperatures. The main observations of this research should greatly contribute to a better understanding of complex degradation mechanisms of modern HV silicone rubber compounds, which are utilized in some of the most critical lines and substations all over the world.
Article
Ureido silane is considered to be a novel tracking resistance additive for effectively improving the tracking resistance property of addition-cure liquid silicone rubber (ALSR). In this work, a series of alkyl-disubstituted ureido silanes (ADUSs) with different alkyl chain structures were synthesized by the transetherification of allyl alcohol (AA) and alkyl-disubstituted ureido siloxanes from the nucleophilic addition between alkyl-disubstituted amides and 3-isocyanatopropyltriethoxysilane (ICPES). The effect of ADUSs with different alkyl chain structures on the tracking resistance property of ALSR was investigated by inclined plane test (IPT), thermogravimetry analysis (TGA), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) and energy dispersive spectroscopy (EDS). The results showed that ADUSs could effectively improve the tracking resistance property of ALSR, especially for (γ-diisopropylureidopropyl) allyloxyethoxysilane (DIPUPAS), (γ-dibutylureidopropyl) allyloxyethoxysilane (DBUPAS) and (γ-diisobutylureidopropyl) allyloxyethoxysilane (DIBUPAS). ALSR incorporated with DIPUPAS, DBUPAS and DIBUPAS passed the inclined plane test (IPT) at the alternating voltage of 4.5 kV and the average erosion mass was only 3.8%, 3.4% and 4.4% of the virgin ALSR, respectively. TGA and TG-FTIR results revealed that DIPUPAS, DBUPAS and DIBUPAS could also effectively improve the thermal stability of ALSR. Accompanying with the weakened oxidation reactions of methyl groups in molecular chains, the formed cyclic oligomers decreased. Meanwhile, the release of methane and cross-linking reaction of the silicone rubber chains were enhanced, leading to the increase of residue under high temperature and the formation of a ceramic barrier layer to protect the silicone rubber matrix. EDS results showed that the carbon content in ceramic barrier layer decreased, which was beneficial to prohibit the development of tracking.
Article
In our previous research on the effect of salt on aging of Room Temperature Vulcanized one-component (RTV-1) silicone rubber material we reported a strong relationship between losses in material mass and hydrophobicity, and potentially significant changes in the mechanical properties of the materials. This is further investigated in the present study, which examines the effects of aging in aqueous salt solution at elevated temperature on the hardness, hydrophobicity, and damage of a selected high quality RTV-1 material. A simple mechanical approach is suggested, which could be used in service to evaluate the amount of aging of RTV materials by correlating changes in hardness with surface conditions such as hydrophobicity. In addition, a new model of aging of RTVs based on the formation of hypochlorous acid in the presence of saltwater on energized silicone rubber surfaces is suggested and supported by Molecular Dynamics (MD) simulations. The diffusion rates of hypochlorous acid, salt ions, water, and nitric acid were numerically compared to determine which aging compound could be primarily responsible for material damage to RTVs under both laboratory and in-service conditions.
Article
In recent years, the room temperature vulcanized (RTV) silicone rubber coatings, widely used in outdoor high-voltage insulators on overhead transmission lines, could improve the contamination performance of insulators. The RTV coatings usually lose its hydrophobicity and result in further degradation under long-term partial discharge. Therefore, it is necessary to study the characteristic of partial discharge along the RTV coated insulation surfaces. The process of partial discharge includes corona discharge, streamer discharge and arc discharge. The streamer propagation along the insulation surface is a complexest physical process. This paper focuses on the characteristics of streamer propagation along the RTV coating. In three-electrode arrangement, the characteristics of streamer propagation along clean and the RTV coated insulation surfaces are measured through three photomultipliers. The electric field required for streamer stable propagation along the RTV coated insulation surfaces is larger, and the velocity is slower in the same electric field. Furthermore, the characteristics of streamer propagation along insulation surfaces with different RTV coating are different. Some RTV coating inhibits the streamer greatly, hence, the characteristics of partial discharge along the different RTV coated insulation surfaces are different in the operation condition.
Article
Insulators in the field experience synergistic effects of temperature, UV radiation, rain, clear mist, and contamination. One of the problems related to outdoor polymeric insulator is erosion and tracking of the weathershed which can affect the reliability of power system. This paper presents investigations on the performance of outdoor 63 kV silicone rubber insulators after seven years of field exposure. The insulator performances were evaluated in laboratory by measurements of leakage currents under clean fog and salt fog conditions. Also visual inspection, hydrophobicity classification and material diagnostic technique have been used to detect defective in service silicone rubber insulators. The polymer content of some surface regions decreased as degradation increased. Scanning electron microscopy, Thermo-Gravimetric, attenuated total reflectance-Fourier transform infrared spectroscopy analysis and energy dispersive x-ray analysis used to identify the elemental composition of virgin and aged surface of insulator. Peak values of leakage current and cumulative charge are measured in clean fog and salt fog chamber. Also, inclined plane tracking and erosion resistance test have been done on the silicone rubber samples. The changes in the surface morphology and material structure were examined before and after the ageing.
Article
Single component room temperature vulcanized (RTV-1) caulks are used in a variety of electrical and other applications. In high voltage Non Ceramic Insulators (NCIs) they are used as part of a triple seal system near the metal end-fittings to protect insulators against environmental stressors including moisture and acid ingress and salt contamination. In service they must resist chemical aging for long periods of time. MacLean Power Systems, Inc. provided three RTV-1 caulk materials for evaluation, of which all three materials maintained their hydrophobicity or increased their hydrophobicity during acid immersion and UV/condensation tests. However, all three materials showed significant mass and hydrophobicity loss upon exposure to salt water at elevated temperatures. Our results show that RTV-1 materials perform differently when compared to Silicon Rubber (SIR) insulator shed materials as reported in the literature when exposed to acid immersion. This is due to the absence of aluminum hydroxide in RTV-1, also referred to as aluminum trihydrate (ATH). Additional acid immersion testing was conducted with ATH resulting in depolymerization of the RTV-1 material.
Article
Room temperature vulcanized (RTV) silicone rubber is a type of anti-pollution flashover coating which has been widely used in China. Featuring good hydrophobicity and adhesive property, RTV coatings are applied to insulators to increase the pollution flashover voltage of insulator strings. However, compared with high temperature vulcanized (HTV) silicone rubber used in composite insulators, RTV coatings are less durable in field operation. In this paper, investigation and experiments were conducted on some RTV coated insulators from Shanxi province and Guangdong province respectively. All the insulators have been in operation for about 6 years and the RTV coatings applied are produced by the same manufacturer. It is found that the performances of RTV coated insulators in Shanxi province are much better than those in Guangdong province. Phenomena such as chalking, color fading and peeling off were observed on RTV coated insulators from Guangdong whereas only slight loss of adhesion property and hydrophobicity were observed on insulators from Shanxi province. Micro structural analysis and macro performance tests were conducted on different positions of collected insulators and it is concluded that operation environment, especially humidity, have great impact on the operation performance of RTV coated insulators.
Article
Full-text available
The changes in the chemical structure and the physical properties of a filled cross-linked polydimethylsiloxane rubber were monitored as a function of various ageing factors. The variables included photochemical, thermal, salt-fog ageings and exposure to acid vapours. Unaged and aged samples were studied by IR spectroscopy, hardness measurements, Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA) coupled with IR spectroscopy. No significant oxidation was detected after all ageings, except for nitric acid treatment. The presence of aluminium trihydrate was clearly identified as responsible for the observed chemical changes. Then an important vulnerability of this filled silicone rubber towards the cross-linking reactions provoked by usual ageings was also detected. The DSC-thermoporosimetry measurements of the mesh size distribution gave a comparison of cross-linking densities for each ageing. The complementary analysis with TGA-IR allowed us to differenciate the thermal stability of the formulation after various ageings and to acquire new knowledge about thermal decomposition.
Article
Full-text available
Cross-linked polyethylene (XLPE) has been the most common insulation applied to medium voltage covered conductors (MVCCs) in Brazil. The results of accelerated aging tests carried out at high voltage laboratory of UNIFEI (LAT-EFEI), combining the stresses of heat and voltage to ground aiming at enhancing surface corona activity assays, have identified the early failures in XLPE insulations of the Brazilian MVCCs. The observed failures indicate that complementary studies should be performed to better understand the degradation mechanisms of the MVCCs insulations manufactured in Brazil. In this paper, x-ray photoelectron spectroscopy (XPS), contact angle analysis (CA), photoacoustic spectroscopy (PAS), x-ray diffraction (XRD), and atomic force microscopy (AFM) measurements on samples of five Brazilian national/regional MVCCs are reported. XPS, CA, and PAS analysis indicated that a large variety of oxygen-containing groups associated to the oxidation of the XLPE insulations appear to be related to the manufacturing conditions. AFM analysis indicated that the average surface roughness and topography of the XLPE insulation changed significantly and depend on the selected manufacturer. XRD analysis indicates a strong heterogeneity of crystals nucleation that results into different degrees of crystallinity of the Brazilian MVCCs cables. The results of this work indicate strong evidences of manufacturing defects in the XLPE insulation of Brazilian's MVCCs. The origin of these defects seems to be inherent to the technology used by manufacturers to the production of the MVCCs. The production-related defects are not detectable by the standard tests as partial discharges or even the standard routine—acceptance power frequency assays routinely used in dielectric compatibility tests at high voltage laboratories.
Article
Silicone rubber (SiR) is widely employed as an insulating material in transmission lines because of its excellent electrical properties and superior performance under wet and polluted conditions. However, the discharges that occur during operation can cause electrical erosion on the surface of silicone rubber insulators. The thermal conductivity of insulators has a correlation with the resistance to tracking and erosion. This study attempts to clarify whether the addition of boron nitride (BN) particles can improve the resistance to tracking and erosion of SiR by increasing its thermal conductivity. Before the tests, specimens were prepared by dispersing nano-BN particles into room temperature vulcanizing (RTV) silicone rubber at different loadings. In this paper, the dc test has been developed from the current IEC 60587 inclined plane tracking and erosion test to compare the phenomena occurring during the tests. Temperature distribution was observed by an infrared thermal imager. The experimental results indicate that the filled specimens have a lower degree of surface damage than the unfilled specimens. In addition, with the increase in content of fillers from 0 to 7 wt%, the thermal dissipation is improved and both the erosion depth and the weight loss show a decreasing trend, which proves the resistance of silicone rubber to tracking and erosion is improved.
Conference Paper
The paper reports on tests done on four commercial room-temperature vulcanized (RTV) silicone rubber high voltage insulator coatings aimed at achieving information on the relative performance of the coatings and the effect of acid-water on the surface degradation. The initial characterization of the coatings includes the identification of the primary filler type, concentration of filler, the amount of free fluid, and the molecular make-up of the free fluid. Soxhlet extraction and gas chromatography tests show considerable depletion of fluid after accelerated aging tests in acid-water and the associated depolymerization on the properties is assessed by changes in hardness. The effect of acid-water aging on the hydrophobicity is assessed by measurements of the static contact angle. The relative comparison of LMW of acid-water aged to field aged coatings gives an idea of the aging process in the field.
Article
In recent years RTV (Room Temperature Vulcanizing) coated insulators have been increasingly applied in South China where the climate is subtropical. In order to investigate the durability of RTV coated insulators for transmission lines a comprehensive series of tests with regard to the characteristics of a subtropical climate were carried out on transmission line insulators which had been in use on 500 kV, 220 kV and 110 kV lines for operation periods of 1 to 6 years. An evaluation of the condition of these field-aged RTV coated insulators on the basis of these tests is given. It indicates that such transmission line coated insulators can operate for a long time and at least for six years.
Article
Purpose: Breast cancer is a major public health issue for women, and early detection significantly increases survival rate. Currently, there is increased research interest in elastographic soft-tissue imaging techniques based on the correlation between pathology and mechanical stiffness. Anthropomorphic breast phantoms are critical for ex vivo validation of emerging elastographic technologies. This research develops heterogeneous breast phantoms for use in testing elastographic imaging modalities. Methods: Mechanical property estimation of eight different elastomers is performed to determine storage moduli (E') and damping ratios (ζ) using a dynamic mechanical analyzer. Dynamic compression testing was carried out isothermally at room temperature over a range of 4-50 Hz. Silicone compositions with physiologically realistic storage modulus were chosen for mimicking skin adipose, cancerous tumors, and pectoral muscles and 13 anthropomorphic breast phantoms were constructed for ex vivo trials of digital image elastotomography (DIET) breast cancer screening system. A simpler fabrication was used to assess the possibility of multiple tumor detection using magnetic resonance elastography (MRE). Results: Silicone materials with ranges of storage moduli (E') from 2 to 570 kPa and damping ratios (ζ) from 0.03 to 0.56 were identified. The resulting phantoms were tested in two different elastographic breast cancer diagnostic modalities. A significant contrast was successfully identified between healthy tissues and cancerous tumors both in MRE and DIET. Conclusions: The phantoms presented promise aid to researchers in elastographic imaging modalities for breast cancer detection and provide a foundation for silicone based phantom materials for mimicking soft tissues of other human organs.
Article
Full-text available
Ultraviolet (UV) aging is one of the most important problems that electrical insulations are faced with it. Generally, total UV radiation emitted from the sun is divided into three parts. Among all types of ultraviolet radiation, UVC has the highest energy because its wavelength is less than 290 nm. Therefore, UVC is definitely harmful for health and even for other objects on the earth including electrical insulators. The objective of the current paper is to study the aging process of silicone rubber insulators exposed to UVC radiation. To accomplish this purpose, three different kinds of commercial silicone rubber insulators were aged by UVC radiation and contaminated solution. Then their electrical and thermal properties as well as their changes on the surface were investigated by measuring leakage current, thermo-gravimetrical analysis and surface elements. It is observed that, the effect of contaminated solution on leakage current is more than the influence of UV radiation alone. In addition, combination of UVC radiation and pollution extremely increase leakage current. Pollution has especially influence on the 3th harmonic component. Aging by UVC shifts the thermal decomposition temperature of the insulations to lower temperatures and degrades the surface of the systems especially the polymers surround the filler. Also it was realized that UVC is able to decompose the filler and reduce the Al/Si ratio in the sample.
Article
Full-text available
Silicone formulations based on polydimethylsiloxane (PDMS) were investigated by using a number of analytical techniques. Horizontal attenuated total reflectance Fourier-transform infrared (HATR-FTIR) spectroscopy studies have confirmed the stability of these materials towards photo-oxidation. No significant oxygenated products were detected after 5000 h of accelerated photo-ageing. However, by using thermoporosimetry, hardness measurements and densitometry, an important vulnerability of these formulations towards the cross-linking reactions provoked by UV visible radiation was identified. Thermoporosimetry, using the solid-solid cyclohexane transition as a textural probe, was also used to visualize the profile of cross-linking inside the materials by calculation of the mesh size distribution in successive slices of 40 µm in thickness. Copyright © 2003 Society of Chemical Industry
Conference Paper
Electrical characterization of materials, including polymers has been performed using electrical impedance spectroscopy. The impedance (Z) spectra gives details about the dielectric dispersion of the resistivity (or conductivity) and the relative permittivity of the material with frequency. This enables one to assess the condition of the material, such as the ripening of fruit, or the aging of polymeric insulators. In this research, Autolab/PGSTAT30 Impedance analyzer was used to assess the aging of 28 kV Thermoplastic elastomeric (TPE) insulators under multistress acid rain conditions. The aged samples showed increased conductance compared to virgin. However, the imaginary Z value (corresponding to the capacitive reactance) of the aged samples were lower than the virgin sample values. The reduction varied for HV and LV samples. The results indicate that impedance spectroscopy can be effectively used to study surface structural modification caused by aging.
Article
A historical background of instrumental approach and landing equipment for aircraft is given beginning with post-World War I efforts of J. D. Doolittle and emphasizing military-civil standardization efforts that began in 1948 and are continuing. The inadequacies of the current Instrument Landing System (ILS) are detailed and the various efforts of special committees to define an eventual replacement system are described. These committees include the Radio Technical Commission for Aeronautics (RCTA), Special Committee SC-117; the NATO Industrial Advisory Group (NIAG) Subgroup (SG-1); and the International Civil Aviation Organization, All Weather Panel (ICAOAWOP). A five-year national plan for development of a Microwave Landing System (MLS) is being carried out under the leadership of the FAA. The goals of the MLS program are stated and discussed. A number of the fundamental issues on system requirements and system design that were decided by the RTCA are described with their alternates. These issues include the use of air-derived data for extracting aircraft position data; the use of precision distance measuring equipment (DME); the requirement to provide flare-out guidance; and the establishment of a two-band approach using frequencies in the C and K u bands. An important issue not resolved was the selection of a technique for providing precision angular measurement of aircraft position. Two approaches are defined: scanning beam and Doppler technique. The basic configuration of a generic MLS is given to establish those functions that are common to both scanning beam and Doppler techniques. The two techniques are then compared in detail to show the advantages and disadvantages of each. The on-going MLS program has as a basic objective the resolution of this issue.
Conference Paper
High voltage insulators have to be used as insulating supporters in various environments in polluted area. The electrical performance of insulators will be degraded. The polluted insulators will have over withstand voltage, flashover can occur easily when the air becomes wet by humidity or fog, which affects on the reliability of the power systems. In order to define effective counter measures against pollution flashovers there are conventional methods such as periodically water washing and also using silicone grease for insulation. Water washing of insulators which is normally recommended so as to remove the pollution from the insulator surface needs to be done more frequently than other maintenance methods. Though involves some limitation in practice from the technical and economical point of view. Applying of silicon grease on insulators with high cost of performance also is not recommended for use in an environment where high level of NSDD pollution is present. In this paper room temperature vulcanizing (RTV) silicone rubber coating have been presented as a novel approach for improvement of outdoor substation insulators maintenance in polluted area. This method can be used in areas characterized with “Instantaneous pollution” and or with “High or Low level of NSDD” with long life expectancy. Financial analysis shows that this method is also economic and optimal choice.
Conference Paper
The paper presents the results of an investigation into the erosion and tracking resistance and the mechanical characteristics of three types of room temperature vulcanized (RTV) silicone rubber coatings for high voltage insulators when subjected to accelerated tests in acid water. Although all coatings have ATH as filler, different performance was observed under simulated acid rain condition. Erosion area, length of erosion and the development of the 3<sup>rd</sup> harmonic in the leakage current during inclined plane tests are employed to evaluate the tracking and erosion of acid aged samples. Thermo-gravimetric analysis (TGA) and thermal conductivity was employed to investigate the thermal performance of the coatings. Scanning electron microscope photographs are also used to assess surface changes after aging. Factors that have significant influence on the aging performance of RTV coatings include filler size and prior treatment, which can improve the performance of RTVs in severe ambient conditions.
Conference Paper
The paper presents the results of an investigation about the aging performance of three different types of room temperature vulcanized (RTV) silicone rubber coatings for high voltage insulators when subjected to accelerated tests in acid water. Although all coatings have ATH as the main filler, different performance was observed under simulated acid rain conditions. Erosion area, length of erosion and the development of the 3rd harmonic in the leakage current during inclined plane tests are employed to evaluate the tracking and erosion of acid aged samples. Thermo-gravimetric analysis (TGA) and thermal conductivity was employed to investigate the thermal performance of the coatings. Scanning electron microscope photographs are also used to assess surface changes after aging. Factors that have significant influence on the aging performance of RTV coatings include filler bonding to the polymer matrix and the existence of other fillers, which can improve the performance of RTVs in severe ambient conditions.
Conference Paper
This work deals with the characterization of the dielectric, rheological and calorimetric properties of different silicone formulations used in power device products such as power modules and inverters. The first part reports the dynamic and kinetic study of the crosslinking process. Important discrepancies are observed between the different compounds that enables a preselection of some polymers. Rheological and dielectric experiments performed on crosslinked samples allow the final choice according to the desired application (encapsulation of electronic circuits in power modules).
Article
Results concerning streamer propagation along cylindrical insulators coated with room-temperature-vulcanised silicon rubber coatings are presented. Experiments were carried out in a three-electrode arrangement consisting of a 12 cm long parallel-plane gap with an auxiliary needle in the earthed anode. Insulators could be inserted between the plane electrodes adjacent to them and almost in contact with the needle. Positive streamers were initiated by applying at the needle electrode a pulse voltage variable in amplitude and propagated over the insulators towards the upper plane electrode which was stressed by a negative DC voltage. The streamer propagation field at conditions from threshold up to the stable streamer propagation and the associated velocity were measured. The dependence of the streamer velocity on the electric field was investigated with the type of coating as parameter. Both the streamer propagation field and the associated velocity of propagation are higher, when a streamer propagates along the coated insulators, than the reference bare nylon insulator depending on the coating employed. Streamers might be used as an effective probe for studying the surface dielectric behaviour of coated insulators hence also for evaluating the various coatings used to improve the contamination performance of outdoor high-voltage insulators.
Article
The paper reports on tests done on four commercial room temperature vulcanized (RTV) silicone rubber high voltage insulator coatings aimed at achieving information on the relative performance of the coatings with respect to aging. The initial characterization of the coatings includes the identification of the primary filler type, concentration of filler, the amount of free fluid, and the molecular species of the free fluid. Soxhlet extraction and gas chromatography tests show considerable depletion of fluid after accelerated aging tests in acid-water and the associated changes to the physical properties is assessed by standard mechanical tests on coupon size specimens. The effect of acid-water aging on the hydrophobicity is assessed by measurements of the static contact angle and the onset of leakage current in an incline plane test. Several field aged coatings are assessed for residual LMW fluid which is compared to accelerated aging tests.
Article
Polymer insulators made of silicone rubber (SIRs) can suffer from algal fouling in tropical and even temperate regions. The purpose of the present study was to understand the hydrophobic behavior and leakage current characteristics of algal- fouled SIR materials when exposed to wet and contaminated conditions. Salt-fog tests were conducted on SIR samples colonized with the treatable alga Chlorella vulgaris . SIR samples covered with non-soluble kaolin powder at a deposition density comparable to that for the alga-treated SIRs were also evaluated. Results show that algal fouling considerably reduced the SIR hydrophobicity compared to the kaolin powder, which resulted in the development of a large leakage current. A major component of the leakage current produced on algal-fouled SIR is dry-band discharge, which leads to material degradation involving tracking and erosion.
Article
The present study evaluated the leakage current suppression and the resistance to tracking and erosion of high-temperature vulcanized silicone rubbers (HTV-SIRs) containing different levels of silicone plasticizer. Slab HTV-SIRs unfilled and filled with alumina trihydrate (ATH, 50 wt%) and with added linear silicone plasticizer (0-6.0 wt%), which was terminated with hydroxyl groups and of which repetition number was 13-18, were tested. Evaluation using the IEC 60587 inclined-plane method indicated that the plasticizer had no influence on the tracking and erosion behavior. Salt-fog test results indicated that a higher level of plasticizer in the ATH-filled HTV-SIR showed smaller leakage current. Gas chromatography and mass spectrometry suggested that the enhanced suppression of the leakage current for ATH-filled HTV-SIR can be attributed to migration of the linear silicone plasticizer onto the surface contaminants. It was concluded that the addition of silicone plasticizer is useful for improving the leakage current suppression ability of HTV-SIR without reducing its tracking and erosion resistance in the above laboratory tests
Article
Silicone rubbers and porcelain intended for outdoor insulation were tested under electric fields at AC 60 V/mm on average for about two years at the field test site at Chubu University. Leakage currents on all materials were characterized and separated into three categories: sinusoidal, local arc, and their transition components. The porcelain allowed a larger leakage current than the silicone rubber samples, for which the cumulative charge of ca. 160 C was recorded in about two years. The cumulative charge of the silicone rubbers was less than 12 C; the cumulative charge of the local arc component, which was likely to be related to surface damage, was less than 3 C. Gas chromatography-mass spectroscopy indicated that the chemical structure change at the silicone rubber surface layer closely resembled that of de-energized surfaces. The dominant aging factor of the silicone rubber in this field test was not electrical stress, but weathering stress such as that resulting from UV radiation. We also performed salt-fog tests of which conditions were adjusted by incorporating non-soluble deposits (kaolin powder) and by changing the salt-fog input duration. The ranking in the salt-fog test was opposite that of the field test. The salt-fog test emphasized the superiority of SIRs to porcelain when compared with the field test. The difference between artificial salt-fog and natural rainfall probably caused such differences
Article
The characteristics of field-aged room temperature vulcanized (RTV) silicone rubber coatings were investigated for use in heavily contaminated areas with emphases on the antipollution flashover performance of aged RTV-coated insulators. An atomic absorption spectrophotometer and ion chromatography (IC) were employed to study the composition of contamination deposited on the insulators, with scanning electron microscopy used to analyze the configuration of the contamination and the aged coatings. The results showed that the sample insulators were heavily polluted with significant changes of the coatings due to field aging compared to new RTV coatings. Flashover did not occur in voltage withstand tests even with high voltage. In addition, the wetting process of the lower surface was not in phase with that of the upper surface during the pollution tests, which increased the pollution flashover voltage on the sample insulators more than the reduced influence on flashover voltage caused by highly soluble salts deposited on the surfaces of the samples. All of the results showed that RTV coatings provided long available term of protection against the pollution flashover, even in heavily contaminated areas
Article
Production survey and seed analysis are presented, and biochemical properties are investigated. Future research aims are stated.
Conference Paper
The present contribution describes an analytical technique which can be used to investigate degradation phenomena of silicones and provide a quantitative evaluation of surface degradation. The technique employed in the present investigation is based on the use of gas chromatography/mass spectrometer (GC/MS) methods
Article
The results of a study on silicone rubber and ethylene propylene diene monomer (EPDM) polymers are presented. The study was done to understand the mechanisms involved in the loss and subsequent recovery of surface hydrophobicity due to dry-band arcing and to investigate various experimental techniques which could be used for characterizing surface hydrophobicity. The materials are subjected to dry-band arcing in a log chamber. Several techniques such as measurement of contact angle, determining surface composition using electron spectroscopy for chemical analysis (ESCA), and measuring crossover voltage (COV) using a scanning electron microscope are examined. The experimental results and theoretical calculations demonstrate that the mobile species in the polymer are responsible for the surface hydrophobicity. In terms of repeatability and simplicity of measurement, the COV determination appears to be the most suitable technique for hydrophobicity studies
The ability of room temperature vulcanizing (RTV) silicone rubber insulator coatings to suppress leakage current, thereby preventing power outages due to contamination, was studied. The RTV coatings were applied to porcelain suspension and line post insulators for a comparative study of the performance of coated and uncoated insulators. A study of the role of alumina trihydrate (ATH) which is used to impart tracking and erosion resistance to RTV coating is reported. A study of the diffusion of silicone fluid from the bulk to the surface of the RTV silicone rubber having various ATH filler levels using attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy is also reported. It has been found that the diffusion rate of the silicone fluid from the bulk to the surface of the coating after extensive dry band arcing decreases with increasing filler level
The loss and recovery of hydrophobicity on silicone rubber surfacecs
  • H Janssen
  • A Herden
  • H C Karner
H. Janssen, A. Herden, and H. C. Karner, "The loss and recovery of hydrophobicity on silicone rubber surfacecs," in 10th ISH, Montreal, Canada, 1997.
Silicone adhesives, sealants and coupling agents
  • W C Wake
W. C. Wake, "Silicone adhesives, sealants and coupling agents," in Siloxane Polymers, S. Clarson and J. A. Semlyen, Eds. Engelwood Cliffs, NJ: PTR Prentice Hall, p. 106.
Technical report on the Long Island solid atmospheric deposition project
  • D Miller
  • N Kikolaidis
D. Miller and N. Kikolaidis, "Technical report on the Long Island solid atmospheric deposition project," Connecticut Department of Environmental Protection, Grant CWF-225-R, 1993.
Evaluation on surface degradation of polymer insulating materials using GC-MS
  • H Homma
  • T Kuroyagi
  • K Izumi
  • C L Mirely
  • J Ronzello
  • S A Boggs
H. Homma, T. Kuroyagi, K. Izumi, C. L. Mirely, J. Ronzello, and S. A. Boggs, "Evaluation on surface degradation of polymer insulating materials using GC-MS," in Proceedings of the 5th ICSD, Leicester, UK, 1995, pp. 575-579.
Chemistry and Technology of Silicones
  • W Noll
W. Noll, Chemistry and Technology of Silicones. New York, NY: Academic Press, 1966, pp. 233-339, 495.