Flashover Characteristics Of Insulators Research Articles

Study on dynamic flashover characteristics of iced insulators

In this paper, based on fxbw4-10/100 insulators, the flashover dynamic characteristics of iced insulators are studied. The insulators are artificially iced and flashover experiments are carried out with water of different conductivity in the laboratory, and different flashover voltages are obtained. The dynamic changes of insulator temperature field, electric field and potential are simulated by using finite element software. Finally, the influence of different physical parameters on insulator flashover characteristics is studied.

Quantitative Analysis on the Influence of Surface Charges on Flashover of Insulators in SF6

In this paper, the influence of surface charges is quantitatively analyzed based on the study of surface charge distribution under DC voltage and flashover characteristics of insulators under superimposed voltage of DC and lightning impulse. It is found that when DC and impulse voltage are in the same polarity, surface charges weaken the electric field along the insulator surface and flashover voltages under superimposed voltage increases. When DC and impulse are in the opposite polarity, surface charges enhance the electric field along the insulator surface, and flashover voltages will decrease. The calculation results of the electric field along the flashover path show that the changing rate of the maximum field strength is approximately equal to the changing rate of flashover voltage, which proves that the influence of surface charges on flashover characteristics of insulators mainly depends on their distortion of the electric field.

Influence of Pollution Degree on Impact Flashover Characteristics of Insulator

The flashover characteristics of polluted insulators under lightning impulse and switching impulse are simulated in laboratory. It is found that when the gray density value is fixed, the flashover voltage begins to saturate under the shielding failure voltage while the salt density value reaches 0.1∼0.15mg/cm2 And the salt density saturation point under the counterattack voltage waveform is earlier than that under the counterattack voltage waveform, around 0.02mg/cm2. When the gray density value is fixed, under the counterattack voltage waveform, the flashover voltage decreases slightly in the gray density of 0.05mg/cm2 to 0.10 mg/cm2 range, and the flashover voltage begins to rise with the increase of gray density. Under the shielding failure waveform, the flashover voltage always decreases in the gray density of 0.05mg/cm2 to 0.20mg/cm2range, and begins to rise gradually after the gray density exceeds 0.20mg/cm2.

In-Vacuum Surface Flashover Characteristics of Insulator With Different Oil Coating Regions

The surface flashover usually occurs on the interface between the insulator and vacuum in a pulsed power system and high-voltage device. In this paper, we studied the improvement of insulator performance in vacuum by covering the transformer oil on different insulator surface regions. We calculated the electrical field distribution to evaluate the influence of oil coating and carried out the surface flashover experiments by oil coating on different regions. The calculated results of the electric field showed that the electrical field magnitude was reduced by coating oil layer and the maximum field located at the electrode triple junction of metal, oil, and insulator. The experiment results showed that the insulator performances with a coating on cathode or anode region were lower than that with the whole surface coating but still higher than that with no coating. Then, the flashover process with a coating on different regions was also discussed. We speculated that the oil layer could restrict the development of secondary electrons and the release of desorbed gas, so the insulator performance could be increased by coating the oil layer on the entire surface, cathode region, and anode region. The insulator performance with cathode region coating and anode region coating was lower than that with entire surface coating due to the electrons avalanche easily moving from cathode to anode.

Study on Influencing Factors of Insulators Flashover Characteristics on the 110 kV True Tower Under the Lightning Impulse

Lightning strike is the main reason for the transmission line tripping. Studies on the insulator flashover characteristics and the accurate flashover criteria under the lightning impulse are the basis for correctly evaluating the lightning resistance performance of the transmission line. In this paper, an experimental study on the flashover characteristics of the insulators with different materials was carried out on the 110-kV double-circuit transmission line tower. The insulators were hung on the umbrella-shaped tower and the drum-shaped tower in the test, and both the standard lightning impulse (1.2/ $50~\mu \text{s}$ ) and the short-tail lightning impulse (1/ $10~\mu \text{s}$ ) were used. The flashover test of a single composite insulator was also carried out for comparatively analyzing the influence of the true tower on the insulator flashover performance. According to the test results on the true tower, the lightning flashover criteria of the insulators with different materials are given. The influencing factors of the insulator flashover characteristics, including the impulse waveform, the insulator material, the tower type, and the insulator suspension position, were further compared and analyzed. Meanwhile, the results of the single insulator test proved that the true tower has great influence on the insulator flashover characteristics and that the flashover test on the true tower can reflect actual situation better and obtain more accurate results. In addition, based on the simulation analysis results of the electric-field distribution around the insulators, the difference of 50% impulse flashover voltage ( $U_{\mathrm {50\%}}$ ) of the insulators in different conditions was partly explained.

Flashover characteristics of cylindrical insulator in high-speed sand environment

With the launching of Lanzhou-Xinjiang high-speed railway in Northwest China, high-speed train running in sand environment will cause strong high-speed airflow with sand around it, which seriously threats the long-term service performance of roof insulators. To study the flashover characteristics of insulator under the condition, a small size wind tunnel system is established to simulate high-speed sand environment, the influence of airflow speed, sand particle size and sand flux on the flashover voltage of cylindrical insulator is investigated. Results show that, in pure high-speed airflow environment, the flashover voltage of insulator has an increase-decrease variation trend with the increase of airflow speed. The flashover mechanism is due to the combined effects of airflow blowing effect and airflow density. In sand environment, flashover voltage will decrease obviously which is caused by nonuniformity of electric field, but the decreasing degree will become small with the increase of airflow speed. Sand particle size and sand flux have negative influence on flashover voltage of insulator. These research results can provide theoretical basis for service performance of roof insulators in high-speed sand environment.

AC flashover characteristics of insulators under haze–fog environment

The occurrence of large-scale haze–fog weather in some developing countries brings a new threat to the safe operation of outdoor insulation. In order to study the effect of the haze–fog on the flashover performance of insulators and the flashover mechanism, kieselguhr, calcium sulphate (CaSO­ 4) and ammonium sulphate ((NH4)2SO4) in different particle sizes were mixed with ultrasonic fog to simulate the haze–fog environment and quantitative ac flashover experiments on the standard suspension porcelain insulator were carried out. The test results indicate that the flashover voltage is related with the pollution degree, particle component, particle size and fog-water conductivity, and may decrease by more than 20% under haze–fog environment. The effect of salt aerosols on flashover voltage is determined by the solubility and larger than that of non-soluble mineral aerosols or organic carbon aerosols. The flashover voltage increases with the increase of the particle size, but decreases with the increase of fog-water conductivity. The flashover of insulator under haze–fog condition is a special kind of pollution flashover in essence.

Significantly improved surface flashover characteristics of insulators in vacuum by direct fluorination

Seeking an insulator supporting high voltage and short pulsed-power electric field in vacuum is an important topic especially for some sophisticated equipments. The voltage breakdown along the surface of insulator in vacuum (i.e. surface flashover) is one of the most serious problems for insulators, and it greatly limits the overall performance of a vacuum-dielectric system. The improvement of surface flashover characteristics of insulators in vacuum become a significant challenge for the development of high voltage pulsed-power devices. Herein, we report a simple and convenient avenue to achieve the high surface flashover performance of high density polyethylene (HDPE) in vacuum based on direct fluorination technique. The physicochemical properties of the fluorinated HDPE (i.e., surface morphology, the chemical component, structure and dielectric capability) were comparatively investigated with the untreated HDPE. The surface flashover characteristics of HDPE in vacuum were mainly discussed. The performance of HDPE at different fluorination temperature was also investigated. The results demonstrated that the direct fluorination strategy developed in this work is an effective means to improve the surface dielectric capability of insulators in vacuum. It is believed to provide a novel possibility for the common insulators applied in high electric field vacuum environments.

Review of high-voltage gas breakdown and insulators in compressed gas

In the past ten years there have been significant advances in the theoretical and experimental analysis of high-voltage gas breakdown and surface flashover of insulators in compressed gases. This has probably been fostered by the recent growth in the design and application of gas-insulated high-voltage equipment. The review describes the characteristics of compressed-gas breakdown, including the effects of failure of Paschen's law; conditioning; electrode area; material and surface; breakdown-voltage distribution; particle contamination; voltage waveform; temperature; and gas mixtures. The insulator-flashover characteristics are then described, including the effects of insulator-electrode interface; insulator material; insulator shape; voltage waveform; charge generation; particle contamination; surface contamination; conditioning; flashover distribution; and dependence on type of gas. The various mechanisms proposed for gas breakdown and insulator flashover are reviewed and discussed in relation to the experimental characteristics. Future theoretical and experimental work is suggested to clarify the gas-breakdown and insulator-flashover mechanisms, and which would also help bring about the design of improved high-voltage gas-insulated systems.

Natural Contamination test of Insulators at Noto Testing Station Near Japan Sea

This paper describes the results of investigation into the performance of various types of insulators energized with 200 kV ac and ±280 kV dc voltages and exposed to natural conditions by the seaside for about five years. DC voltage application had almost the same influence on the salt deposit density as ac voltage application. Salt deposit density and flashover characteristics of insulators were much affected by their types. Flashover voltage for dc is almost the same as that for ac in rms value.