Non-uniform Pollution Research Articles

AC flashover performance of different shed configurations of composite insulators under fan‐shaped non‐uniform pollution

Currently, it is founded that under unidirectional wind and certain landform, composite insulators are always fan-shaped non-uniformly polluted. In this paper, artificial pollution tests on three types of composite insulators with different shed configurations and under various fan-shaped non-uniform pollution conditions were carried out. Then the flashover performances of composite insulators, porcelain insulators and glass insulators were compared. Results indicate that there is a big difference between ac flashover performance of composite insulators under non-uninform pollution and uninform pollution. The flashover voltage of composite insulator is largely influenced by salt deposit density (SDD), the ratio of SDD of windward side to leeward side (W/L), the occupation ratio of leeward side k and the shed configurations. The relationship between SDD and U 50 still meets negative power function when composite insulator is fan-shaped non-uninform polluted. There is a reduction of 17.8–27.6% in the flashover strength when the ratio W/L of SDD decreases from 1/1 to 1/15. The shed configurations of composite insulators have great effects on the flashover performance. Composite insulators always have better withstand property compared to glass and porcelain insulators under either uniform pollution or fan-shaped non-uniform pollution.

Study on the dc flashover performance of standard suspension insulator with ring‐shaped non‐uniform pollution

Under dc electric field, pollution may be more easily deposited around insulator string caps and pins, distributing non-uniformly on its inner and outer parts, and presenting ring-like shape. dc Flashover tests of 7-unit XHP-160 insulator string were carried out. During the tests, the ring-shaped non-uniform pollution was simulated using solid-layer method by changing the ratio I/O of inner-to-outer surface salt deposit density (SDD) and radius (r) of the heavily polluted area (the inner part). On the basis of the test data, the effects of ring-shaped non-uniform pollution on dc flashover characteristics were studied. Then, the relative variation trend of flashover voltage, surface pollution layer resistance, and leakage current were discussed. Research results show that the ratio I/O affects the dc flashover performance of the insulator string. The flashover voltage increases with the increase of I/O. With the increase of the radius r, the flashover voltage will increase at first and then decrease. Under ring-shaped non-uniform pollution, surface pollution layer resistance of insulator will increase, which results in lower leakage current and higher flashover voltage. The results will be of certain value in providing references for outdoor insulation selection.

Effects of ring-shaped non-uniform pollution on outdoor insulation electrical property

The inner area close to cap and pin of insulator is sometimes heavier polluted than the outer area, causing the contamination pattern on insulator surface look like ring-shape. This kind of non-uniform pollution may affect insulator flashover voltage. In this paper, artificial pollution tests of 4 types of porcelain and glass insulators with ring-shaped non-uniform pollution were carried out. Experimental results indicate that the SDD (salt deposit density), the non-uniform pollution degree K (the SDD ratio of inner part to outer part), the heavily polluted area with radius r, and the insulator profile all have significant effects on insulator flashover performance. The effects of K and r on flashover performance can be reflected by the change of pollution layer conductivity during flashover. Under ring-shaped non-uniform pollution, the relationship between Uso and SDD can still be expressed by negative power function, while coefficient a varies obviously with pollution non-uniformity, but exponent n does not. Finally the correction coefficients of flashover voltage considering non-uniform pollution degree K were also calculated for outdoor insulation design.

Leakage current analysis of polymeric insulators under uniform and non‐uniform pollution conditions

This study presents two different methods under uniform and non-uniform pollution layer in order to measure and calculate the leakage current (LC) of silicone rubber insulators. Experimental test for evaluating the LC analysis of polluted insulator have been done in a laboratory clean fog chamber. The electric field and potential distributions were obtained from finite element method software for 3D models. The mathematical background and circuit theory are described in details by a section of insulator and using the extended form factor formula. The surface conductivity used in the calculations was extracted from the measured LC after wetting rate. LC characteristics under 1 : 1, 1 : 2, 1 : 5 and 1 : 10 ratios of top to bottom surface salt deposit density on polymeric insulators are studied. To verify the proposed models of this study, the results of experimental data and two other approaches are compared with together before dry-band formation. Moreover, a dynamic LC model under uniform pollution layer has been introduced and extended in order to calculate the LC when the formation of dry-bands along the insulator surface occurs. The dynamic model is drawn from experimental data and measured surface conductivity.

Contamination characteristics of disc‐suspension insulator of transmission line in wind tunnel

Due to electric field, meteorological conditions and insulator structure, the natural contamination of insulators is complex and so it is difficult to discuss the relationship between various factors and contamination. In this study, contamination characteristics of insulator in a circulating wind tunnel were studied. The results show that speed of the wind and its direction has an obvious influence on the pollution distribution on the insulator and under crosswind, contamination degree of top surface is greater than that of bottom surface and leeward side greater than the windward side. What is more, the contamination characteristics of insulator are affected by wind speed, wind direction, relative humidity (RH) and other factors. Wind speed increment will make its non-soluble deposit density (NSDD) raise and the higher wind speed is, the more obvious non-uniform pollution distribution of windward and leeward side becomes. When RH is up to 90%, the growth of NSDD becomes more rapid. The decrease of particle size and the rise of its concentration, NSDD will increase; the NSDD under uniform wind will increase. The results have certain reference significance for insulator design and selection.

Dynamic model to predict AC critical flashover voltage of nonuniformly polluted insulators under thermal ionization conditions

This paper presents a theoretical dynamic model based on the Hampton criterion and Mayr's equation for predicting the critical values of flashover on the surface of nonuniformly polluted cap and pin porcelain insulators. The nonuniform pollution layer on the surface of the insulator, the number of disk insulator units, and the geometry of the insulator such as diameter and ribs are the important factors used for prediction. Two types of pollution layer configuration, linear and graded, are introduced as nonuniform pollution layers. The influences of the nonuniform pollution layer on critical flashover voltage are investigated. Furthermore, a random value is added to the surface discharge length during propagation in order to consider the effects of the wind and thermal convection on surface discharge length. The specifications of a real porcelain disk insulator are used in the model. Finally, the estimated results of the proposed model are compared with the measured data of the tests in order to validate the proposed model.

Influence of fan‐shaped non‐uniform pollution on the electrical property of typical type HVDC insulator and insulation selection

Affected by long-term crosswind, insulator surface will get coated with fan-shaped non-uniform pollution, which lowers insulator flashover voltage as previous study revealed. In this study, a further research in specific to HVDC line insulation is presented. Taking typical dc insulator as the sample, its dc flashover performance under fan-shaped non-uniform pollution was tested. Then the influence of that kind non-uniformity was investigated through analysing the pollution layer residual resistance, the flashover process and critical flashover voltage. Finally the relevant HVDC insulation selection was made. Research results indicate that: under fan-shaped non-uniform pollution, insulator flashover voltage ( U 50) gets impaired, and is more obviously impaired by ratio J of windward to leeward side salt deposit density (SDD) than leeward side area proportion T ; under various T and J , there is still an exponential relationship between U 50 and SDD; under fan-shaped non-uniform pollution the pollution layer residual resistance decreases, which theoretically promotes the arc propagation and flashover process, and thus finally lowers flashover voltage; for the transmission line in area with fan-shaped non-uniform pollution, adding insulator units to strengthen the withstand property are needed.

Prediction of pollution flashover voltages of ceramic string insulators under uniform and non-uniform pollution conditions

Present paper emphasizes on the development of a new mathematical model to estimate the contamination flashover voltages of ceramic string insulators under varying uniform and non-uniform pollution conditions subjected to AC voltages. The proposed model is developed based on dimensional analysis of the factors which commonly influence the process of contamination flashover of insulators. The new model for string insulators has been validated using previous authors both experimental and analytical results for total of fifteen string insulators including porcelain, glass string insulators and one porcelain log rod insulator. The validation of the new model indicated that results of proposed model for string insulators are in good agreement with published experimental and model results.

Effects of Non-uniform Pollution on the AC Flashover Performance of Suspension Insulators

The non-uniform distribution of contamination on insulator surface has appreciable effects on flashover voltage, and corresponding researches are valuable for the better selection of outdoor insulation. In this paper, two typical types of porcelain and glass insulators which are widely used in ac lines were taken as the research subjects, and their corrections of AC flashover voltage under nonuniform pollution were studied. Besides, their flashover characteristics under different ratio (T/B) of top to bottom surface salt deposit density (SDD) were investigated, including the analysis of flashover voltage, surface pollution layer conductivity and critical leakage current. Test results gave the modified formulas for predicting flashover voltage of the two samples, which can be directly applied in the transmission line design. Also, the analysis delivered that, the basic reason why the flashover voltage increases with the decrease of T/B, is due to the decrease of equivalent surface conductivity of the whole surface and the decrease of critical leakage current. This research will be of certain value in providing references for outdoor insulation selection, as well as in proposing more information for revealing pollution flashover mechanism.

AC flashover performance of various types of insulators under fan-shaped non-uniform pollution

Previous simulation and observations showed that, the air flow field at windward and leeward side of insulator string will probably be different if the wind velocity is over a certain value, and thus causing the imparity of contamination degree at the two sides. In this paper, fan-shaped non-uniform polluting method was used to artificially simulate the different pollution severity at windward and leeward side of insulator string. Then, the effects of fan-shaped non-uniform pollution on ac flashover performance of 5 types of insulators were discussed. Test results indicate that, SDD, the ratio SDD of windward to leeward side (W/L), the occupation ratio of leeward side (k), will affect the ac flashover performance of insulator string. U 50 and SDD still can be expressed by the negative power function. A reduction in W/L from 1/1 to 1/15 would give a decrease about 23% in a value, which causes U 50 reducing about 25%, but n value changes little. The correction method proposed by EPRI is also applicable for fan-shaped non-uniform pollution, but has difference. A larger creepage distance of insulator does not mean that the creepage distance utilization rate is higher. Due to the influence of fan-shaped non-uniform pollution, the existing insulation configuration of transmission lines in heavily polluted areas may not satisfy the required insulation margin. The results have certain reference significance for the design and selection of transmission line external insulation.

Investigations on AC pollution flashover performance of insulator string under different non‐uniform pollution conditions

Observations of contamination tests showed that, the contamination distribution of insulators is usually uneven. In this study, the solid layer method was used to imitate different non-uniform pollution conditions and the AC pollution flashover tests of 7-unit insulators were carried out. The results indicate that the increase of uneven pollution degree J from 1 to 15 will give a 39% raise of U 50 under non-uniform pollution on top and bottom surfaces, a 23% decrease for fan-shaped non-uniform pollution and a 21% higher U 50 with ring-shaped non-uniform pollution. A higher occupation ratio (k) of leeward side will reduce U 50 under fan-shaped non-uniform pollution and a bigger radius R of heavy polluted area has certain effect on U 50 for ring-shaped non-uniform pollution. The U 50 and salt deposit density still can be expressed by the negative power function, and non-uniform pollution conditions and J have great effect on a, but less impact on n. The correction equations of different non-uniform pollution conditions are obtained and the relative errors are acceptable. The research has certain reference significance for the design and selection of AC transmission line external insulation.

Study on the DC Flashover Performance of Various Types of Insulators With Fan-Shaped Nonuniform Pollution

In areas with heavy dust or continuous wind in a single direction, fan-shaped nonuniform contamination at the windward and leeward side of the insulator string may affect flashover performance. In this paper, dc pollution flashover tests of insulators under fan-shaped nonuniform pollution were presented, and a comparison of flashover performance among 7-unit suspension insulator strings with four different disk profiles was made. Then, the influence of fan-shaped nonuniform pollution on flashover voltage, arc propagation, and critical leakage distance were investigated. Research results indicate that the insulators with different types were influenced variously on their flashover stress, utilization rate of creepage distance, and critical leakage distance by fan-shaped nonuniform pollution. A reduction in the ratio W/L of windward to leeward side salt deposit density (SDD) from 1/1 to 1/15 gave a median 35% ± 4% decrease in flashover strength. The extrapolation of results for the seven-unit strings suggests that some increment in shed space or structure height of the insulator can be preferable in dc transmission lines where there is fan-shaped nonuniform pollution accumulating at the windward and leeward side of the insulator string.

DC flashover performance of insulator string with fan-shaped non-uniform pollution

Under continuous wind of single direction, the leeward area of insulator string may be polluted more seriously than windward area, making the pollution layer distributes like a fan-shape. In this paper, dc pollution flashover tests of 7-unit XP-70 insulator string with fan-shaped non-uniform pollution were carried out. Then the influence of fan-shaped non-uniform pollution on flashover voltage, flashover process, leeward side surface layer conductivity and surface pollution layer resistance were discussed. Research results indicate that, the ratio W/L of windward to leeward side salt deposit density (SDD) affects the dc flashover performance of insulator string. A reduction in W/L from 1/1 to 1/15 would give a decrease of 28% in flashover strength. Flashover voltage may also decrease when the occupation ratio (T) of leeward side increases from 10% to 30%. Under fan-shaped non-uniform pollution, U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> can still be expressed by a negative exponential function of SDD, and the effect of fan-shaped non-uniform pollution on U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> -SDD relationship may mainly lie in changing the proportionality coefficient a rather than the exponent n; discharge path was restricted along the leeward side, which may make the air-gap arc easily formed and benefit the flashover process.

A new proposed dynamic arc model for flashover performance of a non-uniform polluted insulator string under HVAC stress

This paper presents a new proposed dynamic arc model of a non-uniform polluted insulator under HVAC stress taking into account the dynamic arc characteristics. The model is based on a hybrid formulation of Obenaus model and the mathematical development of arc equations by Rizk combined with the dynamic equations of the change in arc resistance by Mayr. The model adopts the criterion of Hampton for arc propagation and the model is simulated using MATLAB Simulink. The model can calculate the instantaneous changes in arc current, arc length, arc resistance, and pollution level on insulator string at which the flashover occurs at certain voltage. Practical insulator geometries have been studied to demonstrate the model with non-uniform pollution in different positions and levels of pollution. The validity of the model is verified by comparing the simulation results with the experimental results and previous works.

Artificial pollution flashover performance of porcelain long rod UHVDC insulators at high altitudes

Porcelain long rod insulators are recommended for outdoor insulation of UHV/EHV dc transmission lines because of their excellent service experience obtained in Central Europe. However, very few studies have been conducted on dc pollution flashover performance or the UHVDC insulators at high altitudes. Artificial pollution tests on 300 kN and above porcelain long rod insulators were carried out with dc voltage in natural high altitude areas (about 2000 m), in which the solid layer method was used and the 50% flashover voltage (U50%) was measured with the up-and-down method. Test results show that dc pollution flashover performances of the 300 and 400 kN insulators are similar. The exponents characterizing influence of salt deposit density on the flashover voltage vary from 0.46 to 0.57. A nearly linear relationship between the flashover voltage and the string length of the insulators is presented. Both double suspension strings and tension string patterns have a significant influence on the flashover voltage. The influence of non-uniform pollution distribution between the top and bottom surfaces of the insulator sheds on the flashover voltage is analyzed, and a correction coefficient for the insulators is proposed.

Effect of pollution distribution class on insulators flashover under AC voltage

The aim of this paper concerns the effect of pollution distribution class on insulators flashover under AC voltage. Three scenarios of non-uniform pollution distribution were studied: transversal, longitudinal periodic and longitudinal non-periodic. These scenarios are commonly seen in the field with in-service insulators located near polluting sources and at sites with prevailing winds.In the first scenario, the flashover voltage of polluted insulators under non-uniform transversal distribution is 21% higher than that under uniform contamination. In such a case, the insulator can withstand the voltage stresses much better than under uniform contamination conditions. The flashover voltage of an insulating surface under periodic longitudinal pollution distribution is at maximum 30% lower than that obtained in the same insulation in the case of a uniform contamination. The third scenario has shown the existence of a minimum flashover voltage which is 42% lower than that obtained in a uniform distribution. Laboratory tests revealed that the minimum flashover voltage can be attributed to the maximum shortening of the weakly polluted creepage distance of the insulator before its full flashover. In a so unfavorable situation, it will be necessary either to proceed to a re-dimensioning of the insulation based on their performance under non-uniform contamination or take preventive measures of pollution control of the insulators.

Study on AC Flashover Performance for Different Types of Porcelain and Glass Insulators With Non-Uniform Pollution

The ratio <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> of top to bottom surface salt deposit density (SDD) affects the ac pollution flashover performance of disk insulator strings. The ac pollution flashover stress was established for fifteen different combinations of SDD and T/B in a systematic study, making use of seven-unit suspension strings with six different disk profiles in this paper. Then a comparison was made of pollution performance for glass and porcelain disks with the same profile. The observed relation of ac flashover stress <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EL</i> to SDD and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> followed an equation of the form <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EL</i> = <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> ·SDD <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</i> ·(1- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> ·log( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> )) . The values of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</i> were fitted to test results for glass and porcelain disks of identical bottom-rib profile, and to four other bottom-rib and external-rib profiles. A reduction in the ratio <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> from 1/1 to 1/15 gave a median 26% ± 8% increase in flashover strength, corresponding to the calculated increase in overall pollution layer resistance. Extrapolation of results for the seven-unit strings to UHV dimensions suggests that some reduction in leakage distance can be accepted in areas where there is frequent natural washing of the top surfaces of disk insulators.

Flashover process and frequency analysis of the leakage current on insulator model under non-uniform pollution conditions

In this paper, we present results dealing with the non-uniform pollution carried out under 50 Hz applied voltage on a plane model simulating the 1512 L outdoor insulator largely used by the Algerian Company of Gas and Electric Power (SONELGAZ). Many configurations in non-uniform pollution are studied in the ENP's (Ecole Nationale Polytechnique d'Alger) High Voltage Laboratory in order to analyze the impact of polluted layer distribution on the insulator dielectric performances. The polluted solution has a conductivity of 1.2 mS/cm obtained with distilled water and NaCl. Our investigations are particularly focused on the on line monitoring of both position and width of the contaminated layer. The flashover voltage and the leakage current magnitude have been investigated in order to study the flashover process on this insulating surface. A video apparatus is used to reflect the parallel discharges behavior, appearing when the polluted layer reaches a critical width. Phase angle values between applied voltage and leakage current (LC) signals at the fundamental frequency (50 Hz) are calculated using the Fast Fourier Transform (FFT) spectral analysis. Phase angle measurements indicate that the equivalent impedance of the insulator behaves like RC circuit with a high capacitive effect engendered by the pre-established clean band. This effect decreases when electric discharges occur at a particular voltage level. The Discrete Wavelet Transform (DWT) is adopted for the leakage current decomposition in several time-frequency bands. The STD-MRA (Standard deviation-Multi Resolution Analysis) of these frequency bands is calculated and is employed to choose the most interesting details that detect both position and width increasing of the conducting layer. Reported results show that the pollution surface state and the severity of this conducting layer deposited on insulator surface could be identified from the STD-MRA representation of leakage current frequency bands. It was shown that the high frequency band of the leakage current increases before the final flashover when the polluted layer is located in the middle of the plane model. It was established that a good correlation has been found between the insulator state surface and details of the leakage current obtained through the DWT decomposition. In fact, these details provide relevant information on both position and width of the polluted layer nonuniformly distributed on the insulator surface.

Investigation of flashover voltage and non-uniform pollution correction coefficient of short samples of composite insulator intended for ±800kV UHVDC

Differences in the amount of pollution on the top and bottom surfaces of an insulator have a great influence on the DC pollution flashover voltage. Up to now, many investigations have been carried out on non-uniform pollution flashover performance of porcelain and glass insulators, but very few on composite insulators. In this paper the influence of non-uniform pollution distribution on DC composite insulators on their flashover performance was analyzed, and a correction formula for the non-uniform pollution flashover voltage was proposed, based on artificial pollution tests carried out on short samples of a composite insulator intended for ±800 kV UHVDC. The test results showed that, when the ratio (T/B) of the salt deposit density (SDD) on the top surface to that on the bottom surface is between 1/1 and 1/10, the value of the characteristic exponent a indicating the effect of SDD on the flashover voltage ranges from 0.22 to 0.255. The value of a is nearly independent of T/B. However, the flashover voltage U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> decreases with the increase in T/B. The correction formula indicating the influence of non-uniform pollution distribution on the flashover voltage could be expressed as K=1 - b×log(T/B). For the tested composite insulators, the factor b was 0.141 to 0.156, which is smaller than that of porcelain or glass insulator. That is to say, the influence of T/B on the flashover voltage of the composite insulator is weaker than those on the porcelain and glass insulators.

Effect of non-uniform pollution on the withstand characteristics of extra high voltage (EHV) suspension ceramic insulator string

Pollution flashover of line insulators may cause regional accidents. Research on the effect of non-uniform pollution on the electrical performance of insulators is important for the outdoor insulation coordination. A study on the effect of the non-uniform pollution distribution on the withstand characteristics of an insulator string with 14-unit standard XP-70 ceramic insulators for 220 kV transmission lines is presented. Test results show that ρESDD, N and T/B have their own effects on the withstand voltage of polluted insulator string. And their effects are independent from each other. The withstand voltage of the insulator string increases with the decrease of T/B. By regressing the test results, the relationship between the withstand voltage of 14-unit XP-70 insulator and ρESDD, N as well as T/B is obtained, which can be used in the outdoor insulation coordination of transmission lines. Moreover, the mechanism of the effect of non-uniform pollution distribution on the withstand voltage is analysed. The non-uniform pollution distribution along the insulator surface causes the decrease of the equivalent surface conductivity and the difference of the hydroscopicity between the top and the bottom surfaces, which results in the increase of the withstand voltage and the decrease of the mean root-mean-square value of leakage current.