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The 3D-CT technique, which is a non-destructive method, is used to verify the use of porcelain insulators for overhead transmission lines (OHTL). 3D-CT techniques are often used to detect defects such as cracks in automotive parts or in the medical field. The results of the 3D-CT technique applied to porcelain insulators indicate a clear difference in the size and distribution of pores between new and used porcelain insulators. The most significant difference is the degradation rate of the porcelain insulator. In the case of the used product, the largest pore size of 24 mm2 was found in the cement part exposed to the external environment; however, no pore was found in the new product. In addition, for the used porcelain insulator, 18 mm2 pores were found in the pin head part, which is a part where stress is concentrated; however, few small pores were found at the same position in the new porcelain insulator. Based on the size and distribution of the pores, the areas where the deterioration was the most rapid were identified. The pore area of the cement at the bottom of the cap was five times larger than that at the top when compared to the total area of the cement. This study confirms the size and distribution of defects occurring in the insulator based on aging and provides insight into the long-term reliability and life prediction of insulators. [ABSTRACT FROM AUTHOR]

Porcelain insulators were removed from 154 kV power transmission lines from three locations that were installed between 1969 and 1977. Visual inspection, three-dimensional computed tomography (3D-CT), and X-ray fluorescence (XRF) analyses were carried out. The 3D-CT analysis shows the presence of a number of pores. It was found that the insulating resistance of the porcelain insulators decreases with increasing number of pores and total pore area. Since most of the pores are located in the cement area, it is expected that the decrease in insulating resistance is related to the deterioration of the cement. The XRF analysis reveals that a high percentage of Fe exists in the cap. The Fe 2 O 3 content, which indicates corrosion, is the highest at 95.7% in Region C (48 years), followed by 88.4% in Region A (40 years), and 81.65% in Region B (38 years). High levels of Al 2 O 3 and SiO 2 were detected in Regions B and C where the number of yellow dust days is high. In the case of the cement, the water-absorbing CaO component is 62.87% on average. In Region C where the insulators are the oldest, higher CaO is detected. This shows water absorbion greatly affected the insulation deterioration of the porcelain insulator. It was found that the Al content of the porcelain insulator from Region C, for which the main material is cristobalite, is lower than that from other areas using alumina. The components found by XRF analysis are dependent on the age, the main materials, and the environmental conditions where the insulators were installed. [ABSTRACT FROM AUTHOR]

The development of leakage current on vertical and horizontal strings of RTV coated porcelain suspension insulators in a salt-fog chamber are presented in this paper. Strings comprising of three-units, fully coated, and bottom surface coated, are investigated for leakage current development over a 1000 hour test period. The bottom surface coated insulator strings are used to examine the merits of half-coated insulators in comparison to fully coated insulator strings. Two coating formulations, containing ground quartz in one system, and alumina trihydrate in the other, both at the same filler level, are studied to determine whether filler type affects the development of leakage current, flashover, and their ability to prevent erosion under dry-band arcing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Based on the analysis of the principle and structure of a convolutional neural network (CNN) model used for in-depth learning, an intelligent discriminant diagnosis method for porcelain fuselage insulators in transmission lines is proposed. Firstly, the infrared image of a porcelain insulator is extracted, and then Lenet is used to optimize the network structure. Finally, the model of fixed parameters is formed by training. The model has high classification and judgment robustness and offers accuracy under different conditions such as: temperature, humidity, position of deterioration on the insulator, and thermal load, which allows weight-sharing in the CNN model under different environmental conditions. Based on the experimental data from an infrared heating experiment using a porcelain deteriorated insulator, this work uses the back-propagation gradient descent method to train the model, to form an intelligent detection model for deteriorated insulators. This method has the advantages of high accuracy and robustness, and represents a new method for intelligent detection of deteriorated insulators. [ABSTRACT FROM AUTHOR]

Insulators should be designed to perform both their electrical and mechanical functions, without failure or breakage. This paper aims to illustrate that a newly designed silicone shed with a nozzle requires no maintenance to remove mineral deposits. This new design takes advantage of the constant movement of air to remove the surface deposits that commonly cause erosion and collapse in insulators. This cleaning effect results from the passing air, which removes the deposited particles from the shed surface. This approach works well for a silicone-elastomer-coated shed with hydrophobic features. The results of laboratory experiments designed to reproduce the conditions of insulators in the field indicate that the downstream fluid speed is always higher than the upstream speed when air flows over the new silicone elastomer shed. This ensures that particle deposition on the sheds will be minimal, even over long periods. Furthermore, the silicone elastomers used to construct the sheds have high hydrophobicity which further prevents the deposited particles from sticking and facilitates easy cleaning via the air flowing around the insulators. [ABSTRACT FROM PUBLISHER]

Composite insulator has significant advantages over porcelain and glass insulator for its light weight and anti-pollution flashover performance and has been widely used in overhead power transmission line systems. These advantages would become more remarkable at higher voltage level. In China, silicone composite insulator has been generally regarded as the first choice in UHV and UHVDC overhead transmission systems. However, as a polymer material, the aging threat of silicone rubber has always been a major concern in the application of composite insulators. It is not just important but also urgent to develop specific strategies to evaluate the operation condition of composite insulators and corresponding maintenance methods. In this paper, 65 composite insulator specimens have been collected and studied. A series of tests and measurements have been conducted and all test results have been gathered and filtered based on statistic methods to form the final condition assessment strategies. In this procedure, Fisher Discriminant analysis, Bayes Discriminant analysis and binary-logistic regression method have been applied to establish the relations between the operation condition of composite insulators and the measured data. A three-group and a two-group classification strategy has been developed in this paper to assess the operation condition of insulators. [ABSTRACT FROM AUTHOR]

Long range transmission lines in north-west China are inevitably set up across sandstorm-prone areas. Pollution deposition of insulators working under such rigorous environment is nonuniform due to the influences of flow field and electric field, thus withstand characteristics obtained in traditional artificial pollution test might not be accurate enough. In this paper, sandstorm simulation experiments were carried out to simulate the actual working conditions, and a comparison was made between the withstand characteristics obtained in simulation experiments and artificial pollution tests. The results show that the withstand voltages of insulators went through sandstorm simulation experiment decreased significantly comparing to those prepared by quantitative Brushing Method, which applies the pollution layer uniformly on the insulator surface. Moreover, the withstand voltages of each shed on the insulator string are different at different position and various wind speeds, which reflect the influence of electric field and flow field. In addition, the mechanisms of the influences of flow field and electric field on withstand characteristics of insulators were discussed. [ABSTRACT FROM PUBLISHER]

In order to meet the requirement of mechanical properties, multiple parallel suspension insulators will be used in UHV lines. In this paper, pollution flashover performance of multiple parallel insulators has been investigated based on artificial contamination tests under both AC and DC voltage. Four types of multiple parallel suspension mode are used in the tests, which has 2 strings, 3 strings, 4 strings and 6 strings, respectively. Experimental results indicated that multiple parallel insulators? pollution flashover voltage was lower than that of single string. Study showed that the result is not only affected by the multiple string leads to reduced pollution flashover probability, but also affected by the ionization of air. When the parallel number was less than 4, pollution flashover voltage of multiple parallel porcelain insulators was about 4% lower than that of a single string. If the parallel number was greater than or equal to 4, the value of flashover voltage was reduced by more than 10%. For composite insulators, the voltage drop of the multiple parallel insulators is not as obvious as that of porcelain insulators. In actual project application of the multiple parallel strings, the number of porcelain insulators and the insulation length of composite insulator was proposed to increase. The conclusion of this work can provide technical reference for the external insulation design and construction of UHV transmission lines. [ABSTRACT FROM PUBLISHER]

In this paper, an improved method to diagnose the critical conditions in the porcelain and glass insulators has been proposed through investigating leakage current (LC) and applied voltage signals. Hence, Fast Fourier Transform (FFT) analysis has been used to calculate the phase angle values of the applied voltage and LC signals. Analyzing phase angle difference of LC and applied voltage waveforms demonstrate a strong correlation of the phase difference between the applied voltage and LC waveforms with the insulators conditions. So, the phase difference cosine (P.D%) has been offered as a diagnostic index of porcelain and glass insulators conditions. In this case, when the P.D% value is lower than 30%, the insulators are in clean and normal conditions. On the other hand, if the P.D% is more than 30%, the insulators are in extreme conditions. Moreover, by increasing %P.D value more than 85%, the probability of the flashover occurrence in porcelain and glass insulators will be very high. The obtained experimental results validate the veracity of considering P.D% as a criterion for prediction of flashover in porcelain and glass insulators. [ABSTRACT FROM PUBLISHER]

The paper presents the concept of mechanoacoustic testing of degradation processes of ceramic materials, which is applied to diagnose high voltage insulators in operation. The method depends on the application of slowly increasing compressive loading acting on the sample, with simultaneous recording of acoustic emission (AE) descriptors. The process of loading is continued to the destruction or stopped at different stresses, and the samples are subjected to microscopic examination. Microscopic analysis of the samples enables determining the effects of stress action. The results were compared with the images of similar materials obtained from the insulators after different periods of operation. On this basis, there were distinguished consecutive stages of ageing of electrotechnical porcelain materials and corresponding effects of their structure degradation. Using slowly increasing quasi-static compressive loading in a relatively short-term mechanoacoustic test makes it possible to get results similar to those of long lasting degradation effects in operated electroinsulating objects. Using this method there is possible to describe the factors which affect short and long-term mechanical strength of the tested materials. There is also possible assessment of the validity and application of the theories explaining the strength of porcelains. There was presented research of the influence of the mullite phase on the short- and long-term mechanical strength of electrotechnical porcelain of different types. [ABSTRACT FROM PUBLISHER]

Hardware corrosion on porcelain and glass insulators has occurred on ±800 kV UHVDC transmission lines in China. Iron cap corroded insulators all located at the negative polarity and pin corroded insulators concentrated in positive polarity. The corrosion mechanism is analyzed from the aspect of electrochemistry and the corrosion process is researched by means of spray water simulation tests. Mechanical and electrical characteristics tests and simulation calculation have been done. Test and calculation results indicate that iron cap corrosion can aggravate the contamination accumulation on insulator?s surface and decrease the flashover voltage. Pin corrosion can decrease the mechanical strength of insulators. XP-4C type porcelain insulator and electrolytic cell are used to research the influence factors of corrosion rate of hardware. The test results show that the contamination degree on insulators' surface and its component have considerable influence on the corrosion rate. The more serious the degree of contamination is, the faster the corrosion rate is. The sequence of cation that lead to the corrosion rate from fast to slow is K+>Na+>Ca2+>Mg2+, the sequence for anion is Cl->SO42->NO3-. [ABSTRACT FROM PUBLISHER]

The surface discharge of natural polluted post insulators in rain is an important factor which affects the external insulation of HVDC converter stations. With the artificial contamination flashover tests in rain for porcelain post insulators, this paper has obtained the flashover process and discharge characteristics of the test samples under artificial rain condition. It has been observed that the discharge of water droplet on the shed edge plays a very important role in the whole process of pollution flashover in rain. When a water droplet hangs on the shed edge, the maximum electric field strength appears in the vicinity of vertices, rather than the lateral area of the water droplet. Thus, the streamer propagates only in the direction of the air gap between sheds. Moreover, the influence of raining conditions including intensity and conductivity on the flashover voltage has been investigated. Test phenomena also indicate that due to the different damp and dry band conditions, surface discharge characteristics of post insulator in rain are different with that in fog, which lead to different flashover voltages. This study provides a new understanding for the HVDC insulator pollution flashover in wet environment. [ABSTRACT FROM PUBLISHER]

In order to study the effect of glaze erosion on the performance of porcelain post insulator, an inclined plane (IP) test similar to IEC 60587 standard was conducted on a cylindrical insulator sample under laboratory conditions for ac voltage, and a new test method, called graphite-layer-based glaze erosion test was proposed in this paper and performed on the sheds of a 40.5 kV post insulator. The experimental details of the graphite-layerbased glaze erosion test was introduced, the technical points of which are coating a graphite layer on the surface of the shed using a brush mold which contains multiple hollowed-out rhombic grids, and arranging high voltage electrode at shed root and grounded electrode at shed edge respectively at both ends of the graphite layer, so as to form continuous and stable surface arcing under ac voltage and therefore achieve desired glaze electrical erosion effect. The graphite layer is a uniform viscous mixture made up with flake graphite and liquid glue according to a quality ratio of 1:1.2. The arcing process, arc current characteristics, surface temperature, and glaze erosion appearance were analyzed. Leakage current under power frequency voltage and flashover voltage of the eroded cylindrical insulator by IP test were measured, while porosity test and scanning electron microscopy (SEM) tests were conducted on samples taken from the sheds after graphite-layer-based glaze erosion test. The results indicate that glaze erosion will decrease both electrical and mechanical performance of the porcelain post insulator. The new test method proposed in this paper has been proved to be effective for glaze erosion test and consumes much less time compared with IP test, which provides a new idea for accelerated tracking and erosion test of glaze and porcelain materials so as to study the aging characteristics of porcelain insulators. [ABSTRACT FROM AUTHOR]

In order to provide reference for the operation and maintenance of porcelain insulators on DC transmission lines, the test method for electrolytic corrosion of iron caps was studied in National Engineering Laboratory for Ultra High Voltage Engineering Technology (Kunming) of China, with XZP2-300 porcelain insulators that had no protection zinc collar. The results indicated that the spray water method could simulate the field corrosion condition when the conductivity and volume flow rate were 12 mS/cm and 6-12 L/h respectively, and the differences in the length, width and depth of corrosion area between the test results and the field condition were less than 8%. Besides, the differences in the test results with spray water method from two experimenters were less than 7%. Our study demonstrated that the spray water method proposed in this paper had good equivalence and repeatability, which could be used to research the electrolytic corrosion problem of iron caps of porcelain insulator on HVDC transmission line. [ABSTRACT FROM AUTHOR]

Hardware corrosion has occurred upon lots of suspension-type porcelain and glass insulators of ?800 kV Chusui and Xiangshang UHVDC transmission lines in China since October 2011. The cause of pin corrosion and its influence on the mechanical property of insulators are researched in this paper. The mechanical load that insulator bears under the circumstance of conductor icing and galloping is calculated by means of ANSYS software. Also, the failure forms of insulators under large mechanical load condition are analyzed. On the basis of this, the method that installing organic material sleeve onto the zinc sleeve to vary its corrosion area is proposed. The problem of mechanical strength decreasing of the insulators caused by expansion of corroded by-products is solved. Insulator samples with organic material sleeves of three structures including zinc sleeve half package type, flush type, and whole package type are made, and pin electrolytic corrosion simulation tests are carried out upon the three kinds of samples respectively by means of the spray water method. It turns out that half package type organic material sleeve alters the corrosion part of zinc sleeve effectively and the pins of insulators with two other kinds of organic material sleeves were corroded seriously. The electric field intensity of insulators is calculated by means of ANSOFT software. Calculation results indicate that the semi-conductive rubber sleeve provides the insulator with better electric field intensity characteristic. [ABSTRACT FROM PUBLISHER]

DC artificial pollution tests were carried out on 26 insulators with various shed parameters in high altitude areas to investigate the influence of shed parameters on the flashover performance of composite post insulators. The parameters tested included shed overhang, shed spacing and the core diameter for type A insulators with alternating single large and small sheds and type B insulators with alternating single large and dual small sheds. Ultraviolet photons emitted during partial discharge phenomena in the tests were characterized with an ultraviolet camera, and the arc development paths along the insulator surfaces were observed using a high-speed camera. The results show that the partial discharge phenomena become increasingly intense and arc bridging between the sheds becomes more serious with increasing shed overhang, but these phenomena become weaker with increasing shed spacing. The flashover voltage decreases with increasing core diameter, but increases initially and then decreases with increasing average shed overhang or large shed spacing. An optimal value for the ratio of large shed overhang to large shed spacing must therefore exist and is recommended based on the test results. [ABSTRACT FROM AUTHOR]

Due to the substantial advantage compared to porcelain and glass insulators, Composite insulators have been widely accepted in electric power utilities worldwide. Compared with porcelain and glass insulators, the flashover performance of composite insulators is superior under the contaminated condition, whereas their icing flashover performance should be investigated further. As shown in previous studies, many factors influence the flashover performance of composite insulators under icing conditions. In order to figure out the factors that influence the flashover performance of insulators, experiments were carried out on icecovered energized and de-energized composite insulators under icing condition. The results show that the flashover performances of composite insulators are superior under energized condition compared with de-energized condition. Under energized condition, when icing is light, the flashover performance of different shed configurations is decided by creepage distance. When icing is moderate, the flashover performance of insulator is influenced by water freezing conductivity, shed configuration, creepage factor, and so on. When icing is heavy, most of the sheds are bridged and the configuration of the last few sheds near the high voltage end have important effect on the flashover performance. [ABSTRACT FROM PUBLISHER]

The Rapid Flashover pollution test method (RFO) exposes energized polluted insulators to fog and uses step changes of voltage to identify a minimum flashover voltage. The RFO method reduces test time by a factor of three or more compared to up-and-down voltage application method and is thus time- and cost-effective. In this paper the results from RFO on five ceramic and composite station insulators (line, post and hollow) with median 4.7 m leakage distance are compared closely with duplicate tests using up-anddown procedure. The tests on hydrophobic composite insulators used the preconditioning principles from CIGRE Brochure 555. Full-scale withstand testing of the same five but 420-kV class voltage insulators with median leakage distance 13.3 m are also presented. It is indicated that the flashover test results of RTV-coated station insulators should be specially analyzed and treated. [ABSTRACT FROM PUBLISHER]

In recent years, the phenomenon of electrolytic corrosion on porcelain insulators? iron caps has occurred in many HVDC transmission lines in China such as the Yunguang, Xiangshang, Tianguang, Gaozhao and Xingan HVDC lines. The validity of using U-shaped zinc rings to restrain iron caps? electrolytic corrosion is tested and verified in this paper. In order to research the influence of U-shaped zinc rings on the electric field intensity of insulators, Finite Element Method (FEM) simulation software was used to calculate the surface electric field of insulators with and without a zinc ring. The influence of zinc ring size on the inhibitory effect was studied by accelerated electrolytic corrosion tests, and the reason that zinc rings of the same size exert different inhibitory effects on insulators of different tonnage is explained in terms of iron caps? curvature radii and water pocket characteristics. Test results indicate that the installation of U-shaped zinc rings is useful to suppress iron caps? electrolytic corrosion, and that the inhibitory effect of zinc rings of the same size on insulators with larger cap curvature radii is better than that on smaller ones. Optimal designs of the structure and size of the U-shaped zinc ring and its service life are proposed in this paper, based on the test results and the actual engineering practice. [ABSTRACT FROM PUBLISHER]

When Bipole 1 was placed in service in the 1970s at +450 kVdc, bushings were found to be vulnerable to external flashovers. Bipole 2 at +500 kVdc in the 1980s had bushings with increased strike distance of 1 m and creepage increased from 32.9 mm/kV to 43.6 mm/kV. This made the Bipole 2 bushings vulnerable to radial puncture under non-uniform wetting. Booster sheds were installed to greatly reduce external flashovers of porcelain bushings in both HVDC bipoles. Recently the porcelain clad, oil filled wall bushings of Bipole 1 have been replaced with oil-free composite wall bushings having silicone rubber sheds. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

The paper provides several methods to assess the condition of RTV coated porcelain/toughened glass insulators in the field. Visual observations of arcing and audible corona are the first indications that signal changes to the coating have taken place. It emphasizes that in the absence of reliable data one can use observations based on hydrophobicity to evaluate when maintenance or replacement of the coated insulators is necessary. Life extension strategies are suggested. It also demonstrates that there are differences in the hydrophobicity characteristics among commercially available coatings, and these can be quantified using standard laboratory techniques. Field experience suggests that the life of the RTV coatings can exceed 10 years even under the severest conditions of pollution. [ABSTRACT FROM AUTHOR]

The paper gives the state-of-the-art on pre-coated ceramic insulators for transmission lines. The usage of pre-coated ceramic insulators has mainly been in coastal areas where sea salt causes flashovers of ceramic insulators. The experience to date has been very good everywhere with very few problems reported. Interest in the pre-coated insulator concept continues to be strong everywhere. The paper also provides guidelines to assist the user in the specification of pre-coated ceramic insulators. [ABSTRACT FROM AUTHOR]

The paper presents a nondestructive ultrasonic method of investigating long-rod insulators used on overhead power lines and in substations. A correlation between the degree of degradation of porcelain C 120 and the ultrasonic wave propagation and attenuation parameters was established. The ultrasonic method was used to analyze the quality of groups of line and post insulators after many years of service. Also a new mechanoacoustic method of investigating the stages in the degradation of insulator porcelain was applied. As a result of the investigations carried out on samples of porcelain C 130 the successive stages in the degradation of ceramic insulators during their service life were determined. [ABSTRACT FROM AUTHOR]

Porcelain and toughened glass suspension type insulators that were removed after 25-30 years of service were evaluated in the laboratory with the objectives of understanding failure mechanisms and assessing the condition of similar insulators in the field. The remaining electrical and mechanical strength was highly variable for porcelain and for some they were significantly reduced from the rated value. Scanning electron microscopy and electric field calculations provided an insight into the failure mechanism responsible for electrical strength reduction in porcelain. Toughened glass insulators with shells shattered intentionally in the laboratory (stubs) always flashed over externally and were therefore puncture proof. Multiple explanations are provided to explain this phenomenon based on internal examination of the stubs. The variation in the tensile load to cause failure for toughened glass insulators was smaller when compared to porcelain and was close to the rated value. [ABSTRACT FROM AUTHOR]

The ion migration testing used for dc porcelain support insulators was carried out in this paper. Ten rod samples for dc porcelain support insulators were subjected to a long-term ion migration testing in our laboratory in accordance with the reported procedure of IEC. The changes of Na+ distribution along with the samples under the long-term testing were analyzed, compared to that of the untested samples. The mechanical performance of the tested samples was verified by using bending breakdown testing. The research findings indicate that the ion migration testing designed for support insulators does not cause Na+ ion apparent migration in the samples and does not influence the mechanical performance of the tested samples. [ABSTRACT FROM AUTHOR]

Silicone rubbers and porcelain intended for outdoor insulation were tested under electric fields at ac 60 V/mm on average for about two years at the field test site at Chubu University. Leakage currents on all materials were characterized and separated into three categories: sinusoidal, local arc, and their transition components. The porcelain allowed a larger leakage current than the silicone rubber samples, for which the cumulative charge of Ca. 160 C was recorded in about two years. The cumulative charge of the silicone rubbers was less than 12 C; the cumulative charge of the local arc component, which was likely to be related to surface damage, was less than 3 C. Gas chromatography - mass spectroscopy indicated that the chemical structure change at the silicone rubber surface layer closely resembled that of de-energized surfaces. The dominant aging factor of the silicone rubber in this field test was not electrical stress, but weathering stress such as that resulting from UV radiation. We also performed salt-fog tests of which conditions were adjusted by incorporating non-soluble deposits (kaolin powder) and by changing the salt-fog input duration. The ranking in the salt- fog test was opposite that of the field test. The salt-fog test emphasized the superiority of SIRs to porcelain when compared with the field test. The difference between artificial salt-fog and natural rainfall probably caused such differences. [ABSTRACT FROM AUTHOR]

Vacuum circuit breakers (VCBs) have been developed and widely applied in Japan to meet the requirements of increasing energy consumption and also in national security of various areas. As a result, for example, a 168 kV two break porcelain type and a 100 kA one break VCB have already appeared in the Japanese market and they are currently being exported to world-wide markets. VCBs interrupt currents in vacuum, and this means they do not exhaust dissolved gases which are sometimes harmful to the human body or cause effects on the environment. Therefore, by its nature, the recycling of materials and safety to the human body have been realized, and also no global warming effects would be expected. Energy is extremely essential and important in human daily life, and many types of circuit breakers play important roles in electrical power transmission and distribution systems to maintain the systems reliability and safety by switching the systems under several conditions. Since vacuum circuit breakers possess a lot of advantages such as high current interrupting capabilities, small size, and Low cost, they will be used much more in the future, and at this moment, we believe it is very worthy to discuss and consider thoroughly future trends of VCBs. In this paper, the results of the developments in Japan will be reviewed, the reflection of the results will be stated, and the subjects of engineering in the 21st century will be discussed. These will include recycling, safeguards to the human body and the fireless nature of VCBs; and it will be demonstrated that the developmental works of VCBs are being wonderfully explored in Japan now and in the future. [ABSTRACT FROM AUTHOR]

Aiming at porcelain long rod, disc type and composite long rod UHVDC insulators, this paper presents a comparison of their dc pollution flashover performances and an analysis of arcing behavior at high altitudes (1970m). The solid layer method was used in artificial pollution tests, in which sodium chloride and kaolin powder were used to simulate conductive and inert materials. The insulators were wetted by steam fog in a fog chamber. The 50% flashover voltage (U50%) was measured with the up-and-down method. According to the test results, the three types of insulators are similar in the characteristic exponent which characterizes influence of the salt deposit density on the flashover voltage. Due to lower utilization ratio of leakage distances, pollution flashover voltage gradient for the porcelain long rod insulators is lower than that for the disc type insulators. Whereas covered with Room Temperature Vulcanized (RTV) silicone rubber coatings on the trunk surfaces, the porcelain long rod insulator is much superior to the disc type insulators in pollution flashover voltage gradient. The dc pollution flashover performance and the utilization ratio of leakage distances for the composite long rod insulators are much better than those for the other two types of insulators, which are induced by the special configuration of composite long rod insulators. [ABSTRACT FROM PUBLISHER]

School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona, USA This paper presents a theoretical model for evaluating flashover performance of insulators under contaminated conditions. The model introduces several new features when compared with existing models such as, the formation of dry bands, variations in insulator geometry and surface wettability. The electric field distribution obtained from software for 3-Dimensional models along with form factor are used to determine the dimensions of the dry bands and the onset of arcing. The model draws heavily from experimental measurements of flashover voltage and surface resistance under wet conditions of porcelain and composite insulators. The model illustrates the dominant role played by the insulator shape and housing material on the flashover performance. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]