Pollution Flashover Voltage Research Articles

Influence of inclination angle on the pollution flashover voltage of contaminated silicone rubber

Influence of inclination angle on the pollution flashover voltage of contaminated silicone rubber

Study on the Aging Characteristics of a ±500 kV Composite Dead-End Insulator in Longtime Service.

Composite insulators have been widely used in power grids due to their excellent electrical-external-insulation performance. Long-term operation at high voltage levels accelerates the aging of composite insulators; however, there is a scarcity of research on aged composite insulators operating at 500 kV for over ten years. In this paper, the mechanical, electrical, and microscopic properties were tested on different sheds along a 500 kV composite insulator that had been running for 18 years. Additionally, the results were compared with a new insulator and the standards for live insulator operation. The results showed that the aging of the high-voltage end of composite insulators was the most serious. The results of the physical properties test indicated that the insulator's hardness was compliant but its tensile strength and break elongation did not meet standards. Under wet conditions, the pollution flashover voltage decreases by about 50% compared to the new insulator. Combined with the microscopic test results, the shed skeleton structure could be damaged and the filler might be lost during the aging process of polydimethylsiloxane (PDMS). The hardness of the insulator would increase by the precipitation of inorganic silicon; however, inorganic silicon might destroy the hydrophobicity and other properties of insulator sheds. These results can provide theoretical references for insulator life prediction and operation protection.

Research on Insulation Configuration of 220 kV Bushing in High-Altitude Polluted Areas

The external insulation strength of the power equipment sleeve in the substation and converter station will be reduced with the increase in altitude and atmosphere pollution. The weakness of external insulation seriously threatens the safe operation of electrical equipment. At present, there are few studies and conclusions that focus on the flashover characteristics of power equipment bushing in high-altitude polluted areas. Therefore, this paper takes the 220 kV voltage level bushing as the research object and studies the Alternating Current (AC) pollution flashover characteristics and lightning and switching impulse flashover characteristics at low pressure. The insulation configuration at high-altitude polluted areas is analyzed. Finally, the insulation configuration scheme, which is suitable for high-altitude polluted areas, is proposed. The results show that the AC pollution flashover voltages of the bushing decrease with the decrease in the atmospheric pressure and the increase in the salt density as a power exponent function. The impulse flashover voltages also decrease with the decrease in the atmospheric pressure as a power exponent function. The atmospheric pressure/pollution impact characteristic index is related to the type of voltage, the value of the atmospheric pressure, and the value of the salt density. The test bushing does not meet the insulation configuration requirements in some high-altitude polluted areas. Through the analysis and calculation of the test results, the bushing insulation configuration scheme in high-altitude polluted areas is proposed. The research results can provide a reference for the external insulation design of bushings in substations and converter stations in high-altitude polluted areas.

Robust and Durable Superhydrophobic Coatings with Antipollution Flashover Performance via Silane-Modified Polyurea.

The inadequate hydrophobicity and the degradation in usage seriously hampered the applications of the existing antipollution flashover coatings. In this paper, a superhydrophobic polyurea coating with antipollution flashover ability was fabricated through chemically grafting the silica onto the chains of polyurea by utilizing silane coupling agent and hydrophobic modification. It is demonstrated that the coating exhibits outstanding antipollution flashover performances. Noteworthy, the surface pollution flashover voltage has been increased by 33.8% compared with the room temperature vulcanizing silicone rubber (RTV silicone rubber). In addition, the volume resistivity is above 1.0 × 1012 Ω·m, and the dielectric strength achieves to 28.85 kV/mm, which represents excellent insulating property. Furthermore, the superhydrophobic polyurea coating exhibits outstanding abrasion resistance, adhesion, acid-base resistance, and durability. As a result, it holds great promise for use in preventing pollution flashover in electrical insulators.

Superhydrophobic meta-aramid papers prepared by the surface-embedded spray coating strategy

Meta-aramid fiber (poly(m-phenylene isophthalamide), PMIA) with superior mechanical strength, thermal stability, and insulation properties is a promising fiber material. However, the hydrophilic nature extremely limits its further development in practical applications. Herein, we report on the preparation of the superhydrophobic PMIA papers based on a novel spray coating strategy, by which the coating material is surface-embedded on the PMIA. Owning the unique deprotonation and regeneration characteristics, the PMIA paper is reconstructed with a denser configuration and hierarchical micro-nano surface, supplying amounts of attaching sites for the coating materials of silyl group-modified nano-SiO2. Assisted by the mechanical interlock and electrostatic interaction at the interfaces, a homogeneous and continuous coating layer is formed on the premise of preserving the intrinsic properties of the PMIA substrate. The as-prepared PMIA paper exhibits superior superhydrophobicity with a maximum contact angle beyond 153° and a minimum sliding angle smaller than 2°. This characteristic is extremely favorable for suppressing the surface discharge under various complex operating conditions. Compared with the pristine PMIA paper, the wet and pollution flashover voltages are increased by 194% and 266%, respectively. Furthermore, the correlation between the dynamic behaviors of a water droplet and the improved wet flashover strength is discussed.

Performance Characteristics of Silicone Rubber for Use in Acidic Environments.

Silicone rubber insulators are widely used in power grids because of their excellent performance, but aging has been an inevitable problem of silicone rubber, especially in extreme conditions, such as acidic conditions. In order to clarify the performance changes in silicone rubber in an acidic environment, this paper uses the developed acid-resistant silicone rubber sheet and common silicone rubber samples as the research objects, and conducts an aging comparison test on them in a natural acidic environment. The electrical properties, physical properties, and chemical properties of the two types of silicone rubber specimens with different aging times are analyzed to obtain the performance characteristics of silicone rubber under a natural acidic environment. The research results show that the dry flash voltage and pollution flashover voltage of the acid-resistant silicone rubber after one year of aging are greater than those of the common type; the water repellency of both types of silicone rubber remains in good condition. The silicone rubber produced by our team according to the self-developed acid-resistant silicone rubber formula has indeed played a role in delaying aging in an acidic environment compared with the common-type silicone rubber.

Influence of contamination distribution in characterizing the flashover phenomenon on outdoor insulator

The aim of this work is to model the influence of uneven contamination distribution under various humidity on the pollution flashover voltage of 11 kV porcelain insulator disc. Four scenarios of contamination distribution were proposed to test the sample under various severities of contamination simulated by salt deposit density (SDD). Seriesflashover experiments on contaminated insulators were performed under various conditions. The voltage of flashover under clean condition was appointed as a reference value for analyzing the effect of pollution. Based on the percentage value of breakdown voltage of the contaminated insulator to the clean insulator, the conditions of the tested sample are classified into three categories namely normal (55–60%), caution (45–54 %) and severe (35–44%). In the experimental tests, the uneven contamination area dimension was taken into consideration. An artificial neural network (ANN), derived from experiment results was used as a tool to predict the flashover voltage. The ANN method is built with five inputs related to the geometry of the sample and pollution factors while the flashover voltage was set as the model's output. The results showed that the distribution of pollutants according to the presented scenario has a significant impact on the performance of the flashover voltage. In addition, the error value between the experiment outcomes and the prediction system appeared to be less than 6%. This suggests that the proposed ANN model can be an effective tool in forecasting the insulators’ flashover voltage under test.

Influence of pollution on surface streamer discharge

The outdoor insulators in the transmission lines are apt to accumulate pollution on the surface in the atmospheric environment. The pollution flashover is liable to occur after the pollution becomes wet, which has caused great harm to the stable and safe operation of the power grid. The generation and development of the surface streamer discharge is an essential stage before the pollution flashover. Hence, the research on the characteristics of the surface streamer discharge can reveal the mechanism of the pollution flashover. In the paper, characteristics of the streamer discharge along the pollution insulation surface were measured by three photomultipliers and an ultraviolet camera in the three-electrode arrangement. The streamer stable propagation electric field, velocity, light intensity, and propagation paths along the pollution insulation surface were compared with that along the clean insulation surface. There were significant differences between the streamer discharge along the clean and pollution insulation surface. Furthermore, the pollution layers with different salt densities and ash densities also had an important influence on the surface streamer discharge. These results revealed the mechanism of the pollution flashover, and provided a theoretical and experimental basis for the design of improvement measures for the pollution flashover voltage.

Characteristics of Small-Molecule Migration of Silicone Rubber Insulator in Electrical Power Systems.

The migration of low-molecular-weight components of polysiloxane (small molecules) to the surface of high-temperature-vulcanizing silicone rubber (HTV-SR) ensures its hydrophobicity and tends to coat the surface of pollutants, which would otherwise lower hydrophobicity. The transferability of hydrophobicity will ensure the insulator maintains its higher hydrophobicity after being coated with surface pollutants, thus providing the insulator with higher pollution flashover voltage. This migration process takes a certain time, and in this paper, the time characteristics of hydrophobicity transfer from HTV-SR coated with ten different inert materials were investigated. Ten different inert materials have different migration times and static contact angles, possibly due to the influence of pollution material characteristics on the characteristics of small-molecule migration. Thermogravimetric analysis (TG), Fourier transform infrared spectroscopy (FTIR), and gas chromatography–mass spectrometry (GC–MS) were used to analyze the migration of small molecules to the polluted surface. The evidence of small molecules migrating to the surface of the polluted material over time was found. Furthermore, the influence of pollution material characteristics on small-molecule migration was analyzed via SEM, specific surface area, and porosity. On that basis, the hydrophobicity migration characteristics of mixtures of kaolin and kieselguhr were also studied and compared to determine how best to simulate the behavior of natural pollution using artificial pollutants and their mixtures.

Predicting the DC pollution flashover voltage on the insulation surfaces with superhydrophobicity

Cleanliness and desiccative are necessary for outdoor insulation surfaces to maintain the voltage withstand capability especially in humid and polluted operation conditions. Once the voltage withstanding capability of insulation coatings is reduced by contaminant electrolyte, flashover accidents would be easier to happen, causing tremendous economy and energy losses. Superhydrophobic coatings, due to their self-cleaning property, are deemed to have great application potential in maintaining outdoor insulation performance, especially in humid and polluted environments. The water patterns on superhydrophobic coating in humid and polluted conditions are obviously different from those on traditional insulation coatings. Flashover voltage is one of the indices for quantifying insulation strength, while to date it is still unclear whether the commonly-used flashover voltage prediction models based on Obenaus’s theory are still suitable to be applied in the cases with superhydrophobic surface. Here we proposed a facile and low-cost preparation method of superhydrophobic coating. By analyzing the specific surface condition under humid and polluted conditions, and considering the development of arc path, a novel theoretical model for predicting flashover voltage of superhydrophobic coatings is established from the perspective of electric field. The flashover voltage of the synthesized coating as well as Room Temperature Vulcanized (RTV) silicone rubber coating are tested and compared, for investigating the insulation strength on the synthesized superhydrophobic coating, and verifying the accuracy of the proposed prediction model. It is found the synthesized superhydrophobic coating shows self-cleaning property during the wetting and voltage applying process, the flashover voltage of superhydrophobic coating is higher than that of RTV coating, and is affected less obviously by the change in pollution degree, compared with RTV coating. The established model shows better accuracy in predicting the flashover voltage of superhydrophobic coating than the traditional one, with errors of less than 6%. Based on the proposed model, the flashover voltage of polluted superhydrophobic coating surface is positively and negatively related to the volume and the contact angle of the polluted electrolyte droplet, respectively.

Study on the relationship between the characteristics of water droplets on the shed of composite insulators and the pollution flashover voltage

The anti-pollution flashover characteristic of composite insulators is the main indicators to evaluate their electrical performance, and the pollution flashover voltage can directly characterize the anti-pollution flashover characteristics of the insulators. This paper proposed an on-line detection method for the pollution flashover voltage of composite insulators. Samples of composite insulator shed with different hydrophobicity were prepared by using NaOH solution with pH value of 13 and temperature of 80 °C. According to the distribution of water droplets on the surface of the sample, the characteristic parameter of the number of water droplets was proposed. The samples with different characteristic parameters were smear-stained and used for the pollution flashover voltage test. The relationships between the number of water droplets on the sample surface and the pollution flashover voltage and leakage current were obtained, which can provide guidance for the evaluation of the operation state of composite insulators.

Pollution Flashover Voltage of Transmission Line Insulators: Systematic Review of Experimental Works

Over the past decades, extensive experimental-based research works have been carried out to investigate the flashover phenomenon on the performance of polluted transmission line insulators. The critical focus has been on developing methods that can determine the safety, reliability, and sustainability of the overall power transmission network based on experimental results obtained from polluted insulators’ flashover voltage tests. In this paper, a systematic review of available scientific works, published as early as the 1990s, for the analysis of pollution flashover voltage, is undertaken. The review mainly focuses on factors influencing the efficiency of transmission line insulators under polluted conditions. Specifically, publication databases utilizing various synonyms and keywords associated with the terms “contaminated insulators” and “flashover voltage test” have been scrutinized. The search has resulted in 1364 articles, from which 97 articles have satisfied the review requirements and have been subsequently analyzed to determine the parameters associated with polluted insulators. Major factors that affect the performance of insulators, including electrical and environmental impacts, are discussed. Variations in factors affecting flashover test development and insulator efficiency are also considered. Overall, the current analysis provides an important insight toward successful evaluations of the health of transmission line insulators and research advancements of electric power transmission line insulators.

Influence of Shed Shape on Direct-Current Pollution Flashover Voltage and Pressure Decrease Exponent

This study investigated the influencing mechanisms of shed shape on direct-current pollution flashover voltage and pressure decrease exponent through artificial pollution tests on a glass experimental model in Beijing (50 m altitude) and Tibet (4300 m altitude). Arc development prior to the flashover was quantitatively recorded using a high-speed camera, and three arc development modes along the pollution surface or in the inter-shed space were then extracted through arc development analysis. The occurrence probabilities of the three arc modes under various shed overhangs, altitudes, and shed spacings were analyzed. Mode probability was used to interpret the decreasing flashover voltage gradient with increasing shed overhang and decreasing shed spacing. Research indicates that pressure decrease exponent rises with shed overhang increase, as explained from the perspective of arc development probability. The quantitative relation between leakage distance efficiency and pressure decrease exponent was theoretically derived and its validity was proven through comparing the calculated with the measured.

Research on Flashover Voltage Prediction of Catenary Insulator Based on CaSO4 Pollution with Different Mass Fraction

Pollution flashover accidents occur frequently in railway OCS in saline-alkali areas. To accurately predict the pollution flashover voltage of insulators, a pollution flashover warning should be made in advance. According to the operating environment of insulators along the Qinghai-Tibet railway, the pollution flashover experiments were designed for the cantilever composite insulator FQBG-25/12. Through the experiments, the flashover voltage under the influence of soluble contaminant density (SCD) of different pollution components, non-soluble deposit density (NSDD), temperature (T), and atmospheric pressure (P) was obtained. On this basis, the GA-BP neural network prediction model was established. P, SCD, NSDD, CaSO4 mass fraction (w(CaSO4)), and T were taken as input parameters, 50% flashover voltage (U50%) of the insulator was taken as output parameters. The results showed that the prediction deviation was less than 10%, which meets the basic engineering requirements. The results could not only provide early warning for the anti-pollution flashover work of the railway power supply department, but also be used as an auxiliary contrast to verify the accuracy of the results of the experiments, and provide a theoretical basis for the classification of pollution levels in different regions.

Study on the self-cleaning phenomenon and anti-pollution flashover performance of micro-nanostructure superhydrophobic coating surface under a high humidity environment

Using micro-nanostructure superhydrophobic coating with the unique self-cleaning phenomenon is a feasible method to further reduce the frequency of insulator pollution flashover. However, the research on the anti-pollution flashover performance of superhydrophobic coating is still insufficient. This paper analyzes the various types of forces on the polluted particles accumulated on the superhydrophobic coating surface, and calculates that the vertical force or the horizontal force on the nano-scale and micro-scale particles is positive when they are in contact with most types of droplets. After being fully wetted, these particles are easily absorbed or pulled by the droplets and leave the coating surface. So it is necessary to establish a new DC pollution flashover mechanism model of superhydrophobic coatings surface from the electric field perspective. Based on this model, the relationship between the pollution flashover voltage and the dry flashover voltage is clarified in the state of extremely small leakage current. Furthermore, the anti-pollution flashover performance experiment was carried out on superhydrophobic coating, RTV coating, and uncoated surface to test the leakage current under different conditions. The experimental results show that at any pollution degree, the leakage current of superhydrophobic coating surface always remains about 16.3μA after being completely wetted.

Pollution morphology characteristics on a superhydrophobic surface and its pollution flashover voltage in DC electric field

To solve the pollution problem of insulators on ultra-high voltage DC transmission lines, superhydrophobic coatings were presented and their pollution deposit morphology and pollution flashover voltage in electric field were studied by an artificial pollution deposit system. The experimental results show that the pollution on the surface of superhydrophobic coating is distributed in clusters, which inhibits the chain distribution on the surface of silicone rubber and improves the pollution flashover voltage. Secondly, the competition mechanism of the pollution flashover on the superhydrophobic coating surface was found. This competition mechanism can lead to the failure of the insulation performance of the superhydrophobic coating in severely polluted environments. Finally, a pollution flashover model of superhydrophobic coating is proposed to explain the competition mechanism, which is affected by pollution and the discrete droplets. The conclusions of this study can provide an experimental and theoretical basis for the application of the superhydrophobic coating in the field of UHV DC external insulation.

Influence of Silicone Rubber Coating on the Characteristics of Surface Streamer Discharge.

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.

Pollution Flashover Characteristics of Composite Crossarm Insulator with a Large Diameter

The composite crossarm insulator differs greatly from the suspension insulator in structure and arrangement. This study aims to determine the pollution flashover characteristics of composite crossarm insulators under different voltage grades. Four types of AC composite crossarm insulators with diameters ranging from 100 mm to 450 mm are subjected to artificial pollution test, and then the effects of the surface hydrophobicity state of silicone rubber, core diameter, umbrella structure, arrangement, and insulation distance on the pollution flashover voltage of the composite crossarm insulators are analyzed. Under the pollution grade 0.2/1.0 mg/cm2 and voltage grade from 66 kV to 1000 kV, if the silicone rubber surface changes from HC5 to HC6, the pollution flashover voltage of the composite crossarm insulator will increase by 13.5% to 21.0% compared with the hydrophilic surface. If the core diameter changes from 100 mm to 300 mm, the pollution flashover voltage gradient decreases with the increase in core diameter; if the core diameter changes from 300 mm to 450 mm, the pollution flashover voltage gradient increases with core diameter. Under the same insulation height and core diameter, the umbrella structure will have a certain impact on pollution flashover voltage by up to 1.7% to 5.4%. Under the horizontal arrangement, the pollution flashover voltage can increase by 10.5% to 12.1% compared with that under the vertical arrangement. Under the hydrophilic surface and weak hydrophobicity state, the pollution flashover voltage has a linear relationship with the insulation distance. The above results can provide a reference for the structural design and optimization of the composite crossarm insulator.

Dynamic behaviors and self-cleaning property of droplet on superhydrophobic coating in uniform DC electric field

The application of the superhydrophobic coating is expected to be an effective method to further improve the pollution flashover voltage of insulators. However, so far, the relationship between electric field strength, droplet volume, and sliding angle in strong electric fields is not clear. This is not conducive to the evaluation of the practical application effect of superhydrophobic insulators. In this paper, the self-cleaning property of superhydrophobic coating and the critical motion condition of droplets in the electric field were analyzed theoretically. Then an experimental platform was set up to observe the movement of the droplet driven by the electric field, and the critical electric field strength for droplet motion was measured. Experimental and theoretical analysis results show that the critical electric field strength for positive droplet motion is less than that for the negative droplet. The droplet driven by the electric field can also remove water-insoluble pollution particles. And the maximum pollution concentration that droplets can remove by means of self-cleaning performance is calculated theoretically. The theoretical calculation method of the sliding angle of superhydrophobic coating in uniform DC electric field is obtained, which is in good agreement with the experimental results. This paper provides theoretical support for evaluating the practical performance of the superhydrophobic insulator in strong electric fields.

Prediction of Insulator Pollution Flashover Voltage Based on Data Mining Technology

The pollution flashover of insulators is of great significance to the safe and stable operation of power grids. Therefore, studying the pollution flashover voltage of insulators has very important guiding value for the external insulation prevention of power grids. For this reason, this article has obtained the flashover voltage under different salt densities and gray densities through manual pollution tests. Data mining technology is now widely used. In order to better apply data mining to the insulation flashover voltage prediction,this paper adopts the support vector machine regression method in data mining technology to establish a prediction model to predict the insulator pollution flashover voltage. Through this method, the flashover voltage of the insulator can be predicted in time, which is of great significance for maintaining the safe and stable operation of the power system.