Room Temperature Vulcanized Coatings Research Articles

Effects of TiO2 nanoparticles and silane coupling agents on the adhesion strength and weathering properties of silicone rubber coatings

Environmental contamination on high voltage outdoor insulators can cause leakage currents and electrical flashover and finally reduce the reliability of electric distribution systems. To prevent energy losses and enormous damages, the in-service life of insulators has to be extended. For this purpose, room-temperature-vulcanizing (RTV) silicone rubber coatings are used due to their hydrophobicity. The objective of the current paper is to enhance the weathering resistance and proper adhesion of these coatings to the insulator. In the present study, adhesion improvement was achieved by adding titanium dioxide (TiO2) nanoparticles and silane coupling agents to the silicone rubber. The mechanical properties of nanocomposite coatings were characterized using the pull-off test method. Also, the water immersion method was employed to investigate the weathering resistance. The results revealed that adding TiO2 nanoparticles and silane coupling improved nanoparticle dispersion, adhesion strength, hydrophobicity, and weathering properties of RTV coatings.

Study on the Influence of Accelerated Aging on the Properties of an RTV Anti-Pollution Flashover Coating.

The purpose of this work is to study the accelerated aging behavior of a room-temperature vulcanized (RTV) silicone rubber anti-pollution flashover coating. Red, blue and gray RTV rubber samples were selected to prepare coatings on the surface of stainless-steel sheets. The accelerated aging test was carried out in an aging test chamber according to a four-step program cycle. After the completion of different aging tests, the color difference, glossiness, surface micromorphology, wettability, insulation performance and other parameters of the samples were measured using colorimetry, infrared spectrometry, scanning electron microscopy, and a high-voltage breakdown tester. The results showed that with the increase in aging time, the color difference ∆Eab of the coatings increased. The G60 gloss value decreased gradually and tended to be saturated after 60 cycles. After the aging tests, the RTV coating surface had holes, cracks, peeling and other damage to varying degrees. The C:Si atomic ratio was less than 2, and the hydrophobicity was obviously deteriorated. After aging, the electrical strength of the three RTV coatings decreased significantly. It can be concluded that during the accelerated aging test, the RTV coating had cross-linking and oxidation reactions, and the internal deterioration and surface damage of the coating led to changes in its color, luster, morphology, insulation strength, etc.

Classifying insulator conditions of room temperature vulcanized coated glass insulators under different coating damage modes

The damage of the room temperature vulcanized (RTV) coating on the surface of polluted glass insulators under axial and circumferential directions has a significant influence on the insulator's leakage current and flashover voltage. To date, many investigations have been conducted on the performance of polluted glass insulators under longitudinal, ring-shaped, and fan-shaped coating damage modes. The purpose of this research was to investigate and classify the insulator conditions of RTV coated glass insulators under different coating damage modes using flashover voltage magnitude and leakage current characteristics. The harmonic component index of leakage current used to determine the health status (H) of insulators, and the crest factor (CF) of leakage current, were experimentally extracted and utilized in the classification. The support vector machine (SVM) model with various functions was designed to predict the deterioration configuration of RTV coatings on polluted glass insulators. The results indicate that the flashover voltage and leakage current of polluted glass insulators are significantly affected by different coating damage modes. Specifically, the insulator with the fan-shaped RTV coating damage experiences the most vulnerable pollution effect compared to the undamaged coating, with a 48% drop in the flashover voltage and a 125% increase in the leakage current under heavy pollution. Subsequently, the proposed SVM model demonstrates strong capabilities for predicting the flashover voltage and leakage current and classifying the pollution severity of the RTV coating damage based on the extracted indicators.

Thermal stability of nano RTV vs. RTV coatings in porcelain insulators

Porcelain enjoys high thermal stability and its characteristics determine the life span of porcelain coated insulators in transmission power lines especially under harsh environmental conditions. In addition, room temperature vulcanized (RTV) silicone rubber coating is a reliable maintenance approach to improve performance and lifetime of porcelain insulators. On the other hand, thermal decomposition behavior of polymeric material significantly influences their aging process and there are many studies on enhancement of nanocomposites specifications by adding different types of nanoparticles. In this paper two different types of silicon rubber RTV nanocomposites with low content of modified nano ZnO and nano SiO2particles and pure RTV were compared in terms of their thermal behavior. Modification of nanoparticles and preparation of the coatings were carried out and the products were submitted to different experimental tests. Also, the activation energy was calculated from thermogravimetric analysis (TGA) test as an important factor in thermal aging of nanocomposites. Results of the study suggested that activation energy in the nano ZnO and ZnO/SiO2composites increased in comparison with the pure RTV. This can confirm thermal aging enhancement of the nano RTV in comparison with the pure RTV and can prove helpful in estimating the expected lifetime of the coatings, which is valuable in estimating the reliability of porcelain insulators.

Puncture phenomena and mechanism analysis of RTV coated cap and pin insulators in steep-front impulse voltage test

In recent years, more than 6 million room temperature vulcanized (RTV) silicone rubber coated cap and pin insulators with high mechanical ratings were used in ultrahigh voltage transmission lines in China to improve pollution performance. However, the unexpected puncture phenomena of RTV coated insulators were exposed during steep-front impulse voltage tests; for instance, the steep-front impulse voltage test pass rate decreased to less than 50% for 550 kN glass insulators with RTV coatings. The steep-front impulse voltage test is the most effective method used to check the insulation quality of cap and pin insulators. This unexpected phenomenon once caused serious concerns to power utilities. In this paper, several possible factors that affect the puncture of insulators were analyzed. Then, the extent of the decline in the breakdown of the 550 kN glass cap and pin insulators with and without RTV coatings were studied. The initial puncture location was then found, and the developmental process of the arc on the insulator surface in steep-front impulse voltage tests was observed with an ultra-high-speed intensified charge coupled device camera. Lastly, a breakdown mechanism is proposed. The puncture phenomena of a RTV coated insulator in a steep-front impulse voltage test is essentially an electrical breakdown of the internal insulation. The RTV coating induces the close adherence of the arc to the surface of the insulator. Such closeness changes the arc development path on the insulator surface and facilitates easy breakdown in the shed weak part. All these factors result in a significant increase in the breakdown probability of RTV coated insulators in steep-front impulse voltage tests.

Effects of RTV Coating on the Discharge Characteristics of A Suspension Glass Insulator

DOI : 10.26650/electrica.2019.19024 The present study shows the effects of room temperature vulcanizing (RTV) silicone rubber high voltage insulator coatings on the discharge characteristics of a cap-and-pin type suspension glass insulator. The study covers both laboratory investigations and 3D electric field analysis, considering the coated and uncoated glass insulators. An ultraviolet corona camera is used to detect the location of the discharges, and a partial discharge test system is used to obtain the discharge patterns and pulse magnitudes. The experimental work is only conducted for 50 Hz power frequency voltage. In addition to the laboratory investigations, 3D electrostatic field analysis is performed to determine how the RTV coatings on the glass insulators affect the field distributions. Cite this article as : Ilhan S. Effects of RTV Coating on the Discharge Characteristics of A Suspension Glass Insulator. Electrica, 2019; 19(2): 173-181.

Field aging investigation and filler precipitation analysis on RTV coated insulators in China

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.

Preparation and Performance of RTV Coating for Anti-Pollution Flashover with Superhydrophobicity by Filling CaCO<sub>3</sub>/SiO<sub>2</sub> Composite Particles into Silicone Rubber

Room temperature vulcanizing (RTV) silicone rubber coating with superhydrophobicity for anti-pollution flashover is prepared by filling silica-encapsulated calcium carbonate particles (CaCO3/SiO2 composite particles) into polydimethylsiloxane (PDMS) rubber. Two-step spraying technology is applied for fabricating the superhydrophobic RTV coating film on outdoor insulators. The primary spray coating provides basically the strong adhesion and certain hydrophobicity, and the second one produces the appropriate roughness structure and further enhances the superhydrophobicity. The water contact angle on the prepared RTV coating film is 165°and the sliding (rolling) angle of water droplet is about 5°, allowing water droplets to move easily on the coating surface and give self-cleaning function of the RTV coated insulator surface. The flashover voltage of insulators with superhydrophobic RTV coating is 29.95 kV, quite higher than that of insulators with common RTV coating (23.29) and that without RTV coating (11.34 kV).

Anti-icing performance of RTV coatings on porcelain insulators by controlling the leakage current

Considerable work has been done on preventing ice formation on insulators and the modification of the surface characteristics by increasing the contact angle and decreasing the adherent force have been tried with some degree of success. Heating by electric current has however proved to be an effective and practical method for de-icing transmission lines, but difficult to apply to insulators. A room temperature vulcanized (RTV) silicone rubber coating containing sufficient carbon black to render it partially conducting but not enough carbon to lose its surface hydrophobicity, has been investigated to determine if the heat generated would suffice to inhibit ice growth on the insulators. The heat exchange progress was analyzed and the leakage current through it to prevent ice forming was estimated and coatings developed accordingly. The anti-icing performances of these RTV silicone rubber coatings with different leakage current magnitudes were compared in a climate chamber. The results showed that the surface heating effect, together with the hydrophobicity, could significantly reduce the formation of ice on insulators.

Development of RTV Silicone Coatings in China: Overview and Bibliography [Feature article

The development of room temperature vulcanized (RTV) silicone coatings in China began in early 1985. Over the course of time, they have come to be widely used in China. At present, nearly 800,000 kg of RTV coatings are used every year. They have successfully prevented serious pollution flashover of traditional glass and porcelain insulators and radically reduced the costs of maintaining transmission lines in polluted areas. RTV silicone coatings have been extensively studied in China. The main aspects of the research include improvements in the properties of the formula for better adhesion to porcelain and control of leakage current, the hydrophobicity transference mechanism, and aging. These decades of research have successfully promoted the development of RTV silicone coatings in China. The history of the development and research of RTV silicone coatings in China are discussed in this article.

Investigation on Field-Aged RTV-Coated Insulators Used in Heavily Contaminated Areas

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

Study on hydrophobicity transfer of RTV coatings based on a modification of absorption and cohesion theory

Room temperature vulcanized (RTV) silicone rubber coatings are used increasingly on outdoor high voltage (HV) insulators subjected to heavy pollution. An important property of the RTV coatings is the ability to restore the surface hydrophobicity after a pollutant layer has built up on the surface, which can suppress the development of leakage currents, dry band arcing and flashover. The present study analyzes the hydrophobicity and the hydrophobicity transfer of RTV coatings and the factors that affected the hydrophobicity. A modification of absorption and cohesion theory was used to analyze the hydrophobicity transfer mechanisms and the influences of temperature, polydimethylsiloxane (PDMS) molecular weight, degree of cross-linking, extent of soluble and non-soluble components, and the pollutant properties. The hydrophobicity transfer of RTV coatings was also investigated with various conditions of contaminations and various factors, which affect the hydrophobicity transfer, including the composition of RTV coatings and the outside conditions. Results show that the hydrophobicity transfer of RTV coatings is not only dependent on compositions but also on factors of circumstance. The analysis also explains the obvious difference between the hydrophobicity transfer of RTV coatings to kieselguhr and kaolin based on a particle and surface analysis using the Brunauer, Emmett and Teller (BET) method, which explains the relationship between a BET surface area and the hydrophobicity transfer of the RTV coatings

Influence of thickness, substrate type, amount of silicone fluid and solvent type on the electrical performance of RTV silicone rubber coatings

Room temperature vulcanizing (RTV) silicone rubber coating is increasingly being used by power utilities to overcome the contamination problems encountered in ceramic and glass insulators under wet conditions. The formulation of the RTV coating system is currently undergoing an intensive development in an effort to optimize its performance and in particular to extend its lifetime. While there are many forms of RTV, those used for insulator coating purposes invariably use a base of polydimethylsiloxane. The amount of RTV used in the service application is also important as it impacts on both the cost of the protection offered and on the electrical performance. This paper reports on a study of the influence of the coating thickness, different substrates, addition of silicone fluid to the coating formulation and different carrier solvents on the leakage current, pulse current count rates and the lifetime of the RTV coatings. It has been found that all these parameters affect the electrical performance under wet and contamination condition in a salt-fog. The optimum coating thickness has been determined for a fixed substrate. Mechanisms by which these four parameters affect the performance are suggested and discussed.

Protective coatings for improving contamination performance of outdoor high voltage ceramic insulators

This paper presents an overview of the practices employed by utilities and industries to combat the contamination problem with ceramic insulators. It emphasizes two popular methods, namely, coating insulators with greases and RTV (room temperature vulcanizing) silicone rubber coatings. The experience to date, application methods, user concerns, current theories on how and why the coatings perform, life expectancy, and future direction of the technology, are outlined. The paper also describes research activity in the committee on RTV coatings, which is the state of the art in protective coatings.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of saline-water flow rate and air speed on leakage current in RTV coatings

Room temperature vulcanizing (RTV) silicone rubber is increasingly being used to coat porcelain and glass insulators in order to improve their electrical performance in the presence of pollution and moisture. A study of the dependence of leakage current, pulse current count and total charge flowing across the surface of RTV on the flow rate of the saline water and on the compressed air pressure used to create the salt-fog is reported. The fog was directed at the insulating rods either from one or two sides. The RTV was fabricated from polydimethylsiloxane polymer, a filler of alumina trihydrate (ATH), a polymerization catalyst and fumed silica reinforcer, all dispersed in 1,1,1-trichlomethane solvent. The saline water flow rate was varied in the range 0.4 to 2.0 l/min. The compressed air pressure at the input of the fog nozzles was varied from 0.20 to 0.63 MPa. The air speed at the surface of the insulating rods was found to depend linearly on the air pressure measured at the inlet to the nozzles and varied in the range 3 to 14 km/hr. The leakage current increased with increasing flow rate and increasing air speed. This is attributed to the increased loss of hydrophobicity with a larger quantity of saline fog and a larger impact velocities of fog droplets interacting with the surface of the RTV coating.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Chemical changes at the surface of RTV silicone rubber coatings on insulators during dry-band arcing

Under wet and contaminated conditions dry band arcing occurs on the surface of HV outdoor insulators coated with room temperature vulcanizing (RTV) silicone rubber. The thermal impact of the arcing on the surface of the RTV causes chemical changes. The gradual loss of hydrophobicity due to dry band arcing is of considerable concern because it results in a reduction of the withstand voltage and subsequent failure of the insulator and power outage. In this study the RTV coatings were subjected simultaneously to salt-fog and electrical stress. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and electron spectroscopy for chemical analysis (ESCA) were then employed to investigate the chemical changes. Possible chemical reactions and processes occurring under dry band arcing are suggested. The results of ATR-FTIR and ESCA indicate the formation of low molecular weight polydimethylsiloxane (PDMS), the reduction in the surface density of CH3 groups and crosslinking of the PDMS backbone chains at the surface. Chemical derivative analysis was also carried out to further elucidate the chemical changes on the surface of RTV coating.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hydrophobic behavior of insulators coated with RTV silicone rubber

Room temperature vulcanizing (RTV) silicone rubber coatings are applied to electrical insulators to improve their subsequent insulation strength, particularly under wet conditions. Under prolonged wetting the hydrophobicity of the coating is reduced temporarily and the insulator protection is lost. After a dry period, a recovery of the hydrophobicity takes place. To investigate this phenomenon, the surface was subjected to various wetting conditions with and without electrical stress. Measurements of the contact and the sliding angles were used to determine the state of the surface. Using water, the surface free energy of the RTV was calculated from the contact angle measurements as a function of time of exposing the surface to salt-fog. The surface free energies due to London dispersion and hydrogen bonding forces on the surface of RTV coatings were calculated from the contact angle measurements using both water and methylene iodide. Good agreement was obtained with the literature value for a virgin RTV surface. The chemical changes of the surface are shown to be responsible for the loss of hydrophobicity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparison of RTV silicone rubber coatings under artificial contamination in a fog chamber

A comparison is presented of the electrical performance of room-temperature vulcanized (RTV) silicone rubber coatings for insulators under artificial contamination produced in a salt-fog chamber with DC voltage. Comparison of the RTV coatings with silicone grease coating has also been made. Correlation of the electrical parameters, such as leakage current and flashover voltage, with material degradation due to aging produced by dry band arcing is established. It is demonstrated that there are distinct differences among the RTV coatings evaluated, and between RTV coatings and silicon grease. >

Effects of filler level in RTV silicone rubber coatings used in HV insulators

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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rain and contamination tests on HVDC wall bushings with and without RTV coatings

Results of tests made to determine the ability of room temperature vulcanized (RTV) silicone rubber coatings to improve the performance of HVDC wall bushings are described. The behavior of uncoated full-scale +or-500 kV wall bushings is first determined in wetting conditions consisting of nonuniform rain and fog with various amounts of predeposited surface contamination. Parameters affecting flashover performance, such as polarity, rain conductivity, and contamination severity, are discussed. Results of nonuniform rain tests on an RTV coated wall bushing are reported. Fog tests and in-service experience have demonstrated that RTV coatings improve the HVDC contamination flashover performance of station post insulators; no flashovers occur in laboratory clean fog tests at rated voltage with ESDD levels up to 0.1 mg/cm/sup 2/. The application of RTV, silicone grease, or oily coatings makes the surface of a wall bushing sufficiently hydrophobic to prevent flashovers during nonuniform rain tests without a pre-deposited layer of contamination.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>