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Tuned liquid dampers (TLDs) and tuned mass dampers (TMDs) have been widely used in suppression of structural vibrations. However, the combination of TLDs and TMDs has been rarely investigated. This paper proposes a new vibration suppression system that combines sloshing liquid with tuned mass immerged in it. The vibration attenuation process of the combined system without structure damping is numerically simulated and characterized by using an implicit coupling approach of segregated solvers. The simulation results indicate that the proposed system, tuned immersion mass with liquid damper (TIMLD), can dissipate energy with liquid sloshing while maintaining the energy absorbing capacity of the mass by resonance. Thus, it exhibits a better vibration suppressing performance than conventional vibration suppression systems such as TLD and TMD. The energy absorbing capacity of the combined system with sloshing liquid is much better than that with liquid filled fully. Distinguishing liquid free sloshing frequency significantly from vibration frequency helps the mass to maintain its energy absorbing capacity by resonance. Affected by the resonant structure and excited by the mass, liquid sloshing can dissipate energy significantly, which constitutes the mechanism of vibration suppression of this proposed system. In light of this mechanism and in an attempt to guarantee the mass resonance and to increase the energy dissipation of the liquid, the combined system has been optimized and characterized.

RTV coatings had been widely used in electric insulators to prevent pollution flashover performance at external insulation. For the bad weatherability of polymers, RTV coatings will be aging during the long serve time. To remove the aging coatings, many methods had been used, such as solvent dissolve, high pressure water flushing, and dry ice flushing. But it is not easy for these methods to remove the coatings entirely and easily. In this paper we described a new method-laser cleaning, which is a very easy and useful method. We used the continuous laser with Ytterbium Laser System (YLS-2000) and the pulsed laser with IPG fiber laser system (Nd:YAG) in the experiment. Different scanning speed of the laser irradiating and different energy density had been tested to find Optimization parameters which could remove the coatings and not damage the surface of the glass insulators. The both laser irradiating can remove the coatings clearly in the experiment. But the continuous laser will leave the carbon clusters on the surface, which is easy to remove but bad for the insulators. The scanning speed can be higher than 10 mm/s that means the glass insulators with 20mm diameter can be dealt in 3 minutes with pulsed laser. The laser cleaning is a good method to remove the RTV coatings on the glass insulator surfaces up and down. With the cost of laser technology decreases, it will be a better method as a coating removing method.

This paper descirbes leakage current characters and discharge phenomenon of outdoor insulators both in the lab and in the field. The results are hoped to be used for online monitoring of the contamination levels. The following contents are introduced in the paper: leakage current monitoring systems, relationships between leakage current and discharge phenomenon, flashover prediction methods and its applications in the field. The leakage current monitoring system is introduced firstly. Then the relationships between leakage current and discharge phenomenon for both suspension insulators and post insulators are presented based on the laboratory tests. A new parameter (I * ) that accounted for maximum leakage current (Ih) and different insulator shapes is introduced to estimate the flashover voltage for different kinds of pollutant layers when they are saturated with moisture. Meanwhile, the relationships between relative humdity (RH) and maximum leakage curren, altitude and maximum leakage current are investigated. With these results a flashover prediction method is developed. Ih measured in different relative humidity is converted to I * for the same contaminate layer when it is saturated with moisture. Then the flashover voltage is estimated by I * . Furthermore, an online leakage current monitoring results are analyzed. The relationships between leakage current characters in the field and ambient relative humidity are analyzed. The results show that although there are some differences between the leakage current in the field and in the lab because of some especially serve atmospheric conditions, the relationships are similar. Meanwhile, leakage current waveforms in different weather conditions are investigated. The waveforms of leakage current in the field are similar with those in the lab. The leakage current waveform that accounted for strong arc is found in the field. Finally, the contamination level of the field insulator is evaluated. The results corresponds well with the local condition.

A weakly luminous layer close to the anode is observed at time far ahead of the current pulse in dielectric barrier discharge of helium at atmospheric pressure and it is considered as the result of a very weak Townsend discharge. Based on the assumption that the space charge produced by this Townsend discharge is too small to distort the uniform electric field in the gas gap, the electrons have more or less the same energy over the entire gap and the spatial distribution of the discharge light is proportional to the distribution of electron density. This light distribution is obtained by processing side-view photograph of discharge gap using an intensified charge coupled device camera with an exposure time of 20 ns. By fitting a theoretically derived formula with the measured curve of light distribution, the Townsend electron ionization coefficient a is determined to be 31 cm−1 at E/p = 3.6 V·cm−1·Torr−1, which is much higher than that obtained by solving the Boltzmann equation of pure helium. It is believed that penning ionization of helium metastables with impurity of nitrogen molecules makes great contribution to the experimentally determined α value. The contribution of this penning ionization to α is roughly estimated.

High voltage equipments, especially polymer insulators may be getting into aging conditions due to the existence of corona discharge on the surface after a long term of running, which would accelerate the deterioration of the surface insulation performance, and even make equipments step into calamity ultimately. So it is significant to detect corona discharge on surface to ensure insulators' stable running. This paper presents the development of a novel corona discharge detection system based on photomultiplier tube (PMT), which has good functions of distance detection for corona discharge in determined region from surface of high voltage equipment and corona characteristics data analysis. In the verification experiments, it was shown that UV corona light can be also taken as characteristic for detecting corona discharge, other than corona leakage current detection, and a linear relationship was shown between the light magnitude and the current magnitude. Furthermore, mean peak value and number of pulses whose peak value is above threshold are extracted from the basic data, which can be used to quantify the development of corona discharge. The results of investigation on polymer insulators suggested that detection of the region between metal end fitting and first shed should be emphasized. The measurements of corona discharge distribution along insulators can be used to learn about the degradation conditions. Detection of polymer insulators in lab and field inspection experience are both soundly verifying the usefulness of the corona detection system.

Composite insulators were extensively applied in outdoor insulation for the extraordinary performance of hydrophobicity and anti-aging property. Whereas HTV silicone rubber had low elastic modulus and the stiffness was not high enough to resist high speed wind. In northwest China there are many storm-wind areas where the designed wind velocity of transmission lines could reach to 42 m/s. The high speed wind induced sustained and intensive oscillation of insulator sheds and finally leaded to fracture failure at root of it. The oscillation problem of sheds and fatigue and fracture properties of HTV materials haven't been paid enough attention before, for the composite insulators utilized in strong wind area. This paper researched on oscillation performance of one type of composite insulator in wind tunnel with applied wind speed from 0 m/s to 60 m/s. The oscillation phenomenon was recorded with high speed camera to measure the oscillation magnitude and frequency. Four HTV silicone rubber samples were tested for its fatigue resistance performance. The developing process of crack along the groove of silicone rubber samples was observed and the flexing cycles and the cycles that the micro-crack developed into fracture were measured.

In this paper a new mathematical model of secondary frost heave is presented. It is expected that the problem considered under some assumptions is well-posed.

The development of composite insulators in China dates back to the early 1970's. In the 1990's they have become widely used in China. At present, up to 600000 composite insulators are operating on 35 to 500 kV ac overhead transmission lines. They are to be introduced into the 500 KV HVDC transmission schemes. In China all composite insulators in service are silicone rubber and are operating in various Contamination conditions. They have successfully and efficiently avoided serious pollution flashover, which occurred frequently when conventional ceramic insulators were used, and radically reduced the maintenance cost of transmission lines in pollution areas. Study of composite insulators is very active in China. The main aspects include properties of materials such as silicone rubber and fiberglass reinforced polymer (FRP) rods, electrical and mechanical performance, aging as well as evaluation and inspection of composite insulators. These fruitful works greatly promote the development of composite insulators in China.

In this paper we deal with a class of free boundary problems (1.1)–(1.8), which comes from the “secondary frost heave” problems. We prove the global existence andw uniqueness of solutions to them, and the results corresponding to diffraction problems are also new.

During the pollution flashover process, streamer discharge is a very important stage before arc formed. In the paper measured the streamer propagates between two parallel plane electrodes by using three-electrode structure, and compared the characteristics of propagation while contamination with different ESDD and NSDD was brushed on the insulator surface, and simulated the distribution of electric field on insulator surface before and after the contamination was brushed by using Ansoft analysis software. The results showed that: the ESDD(or NSDD) increases, Eth increases first, then remain unchanged. After the applied field is greater than Eth, velocity of different ESDD and NSDD is similar. Through simulation found that the presence of contamination distorts the electric field distribution on insulator surface. The electric field of contamination area was obvious reduced and enhanced on both ends of the area. The change in conductivity of contamination makes the electric field distribution changes, and then causes the differences of the waveforms and field required for stable propagation of streamer.

In order to evaluate the operating characteristics of RTV anti-pollution flashover coatings used in Guangdong Province, a series of experiments and tests were carried out on RTV coatings operating in different natural environments with operating periods ranging from 3 years to 8 years. The research results showed that the appearance of coatings were affected by operating years, pollution areas, pollution sources and methods of suspension. There was different hydrophobicity on different location, and the weakest hydrophobicity located on the outer part of upper shed. The hydrophobicity of coatings was affected by the types of pollution sources. The flashover voltage of coatings was directly affected by the hydrophobicity distribution. There was a certain correspondence between the appearance and the flashover voltage of anti-pollution flashover coatings.

Defects of high-voltage transmission lines are often accompanied with corona discharge; and corona discharge would produce ultraviolet. Based on this principle, the UV imager can be used in detecting the defect. Electric field strength is the main factor affecting the corona discharge, which is determined by power-supply and experimental model. In this paper, UV measurement of different defects was studied, and the effect of Applied-voltage on corona discharge of defects was acquired. A quadratic relationship exists between the UV strength produced by corona discharge and applied voltage. The quadratic coefficient A is between 0.31~0.37, which is increase with the length increasing at the experimental conditions in this paper.

Pulsed electric field is a novel non-thermal process technology. It could be applied in the extraction of functional components from plant for its irreversible disintegration on plant cell membrane. PEF treatment caused an irreversible disintegration on the cellular membrane of raspberry cell and the extraction yield of anthocyanins from raspberry was linearly correlated to the treatment pulses of PEF. During the extraction, Cyanidin-3-glucoside, the major anthocyanins in raspberry was found to be significantly degraded by PEF. The degradation effects of Cyanidin-3-glucoside decreased with the increase of the electric field or treatment time. In the spectra curves of Cyanidin-3-glucoside treated by PEF, the intensity of the peak at 333 nm increased as electric field and treatment time increased, while the intensity of the peak at 519 nm and the shoulder at 430 nm decreased, indicating Cyanidin-3-glucoside was degraded into chalcone.

Loose stator slot wedges could result in excessive vibration of the stator coils in large generators, which would accelerate the deterioration of the groundwall insulation and even eventually lead to catastrophic failure of large generators. So it is significant to detect loose slot wedges in stator slots to ensure generatorpsilas normal operation. Up to now, the slot wedges used to be tapped by hand using a small hammer with the operator making a judgment of tight or loose based on the sound from the slot wedge. This method is workable and has provided much useful data on the condition of the generators, but suffers from a few of major problems. This paper was concerned with its vibration characteristics in the loosening process of slot wedge with different fixing style and, introduced a slot wedge automation tester which was developed with Digital Signal Processor (DSP) technology and embedded system theory. It is a portable tester, and easier for workers to use to judge the tightness of slot wedges than the traditional manual method. It has also been applied to test stator slot wedges of some large generators in China.

HV outdoor insulating systems such as line and station insulators, surge arresters and bushings, using silicone rubber for outdoor insulation have become very popular. This paper presents the mechanical behavior and electrical behavior of silicone rubber blend with different fillers. Various loadings of alumina trihydrate (ATH) and silica are added to silicone rubber and their performance are evaluated. Different types of silica such as fumed silica and precipitated (ppt) silica are studied. It was found the type of different silica filler makes difference in mechanical properties and dielectrical properties. And it was also found silane treatment of precipitated silica have great influence on the performance. The test results show that the more addition of ATH, the better the erosion resistance is achieved, but will result in declined mechanical properties.

Contamination flashover is one of the most serious problems in power delivery system. Leakage current that flows over the surface of the contaminated insulators is considered the main causation of this problem and a lot of researches have been carried out to study the characters of it. But the relationships between leakage current characters and relative humidity are still not clear. In this paper, two typical cap and pin insulators were used in the artificial pollution tests that carried out in a relative humidity (RH) controllable chamber. Leakage current waveforms on the insulating surface were recorded during the tests. The characters of leakage current waveforms under different ESDD and relative humidity in both time and frequency domain were analyzed. In the results, the relationships between frequency characters, ESDD and RH were presented. A means of flashover prediction that based on the frequency characters of leakage current was discussed at last.

Using a high-speed camera, the fundamental behaviors of arcs on the surfaces of two types of 300 kN porcelain insulators were studied under DC voltages. The test results showed that it was quite easy for the arcs on porcelain insulator surfaces to levitate from insulator surfaces in high altitude areas (1970 m). The influence of angles, used for different V-strings of insulator configurations, on DC flashover behaviors of contaminated insulators was very obvious. In this paper, the effects of the angles of V-strings on DC flashover characteristics of two types of polluted insulators (anti-fog insulator and tri-shed DC suspension insulator) were investigated.

It has been investigated that the effect of relative humidity on statistical parameters of negative corona pulses at different air pressure conditions. A rod-plane electrode configuration has been used. The range of air pressure and relative humidity is 0.06 MPa~0.10 MPa and 30%~90% respectively. The variation of average amplitude and standard deviation of negative corona pulses is illustrated. Average amplitude and standard deviation of negative corona pulses are lowered, as the air pressure or relative humidity rises. It is demonstrated by the ratios of average amplitude under different conditions that the degree of influence of air pressure (or relative humidity) on average amplitude becomes more pronounced at higher relative humidity (or air pressure). The linear relationship exists between average amplitude and the square root of the product of air pressure and relative humidity. While between standard deviation and the product of air pressure and the square root of relative humidity are the second order relationship. It means that the degree of influence of air pressure and relative humidity is the same on average amplitude, but different on standard deviation

Summary form only given. Nonthermal atmospheric plasma which can be produced by dielectric barrier discharge (DBD) has many applications in textile surface modification, which demands highly on the uniformity of the DBD. Based on the experimental setup in our laboratory, gas flow was found to be a very important factor to influence the state of the DBD and the experimental results are discussed in this paper. The results show that, in the DBD, not only can the gas flow decrease the working discharge voltage of self sustained discharge, but also it can improve and maintain the uniformity of the discharge. The optimized flow rate is advised

To prepare uniform nanofibers from poly (ethylene oxide) (PEO), a voltage of 0 to 15 kV was applied to a distance of 15 cm to 30 cm between tip and ground collector. In this study, jet current and Taylor cone were used to express the electrospinning stability. It is showed that an electric current during electrospinning affects the fiber morphology. SEM and jet current monitoring were used to study the jet stability with positive power. It is suggested that it may be concluded that there is a voltage range for spinning with these conditions. The most important one is the Taylor cone shape. When jet current is at the smaller ratio of slope and the Taylor cone still has a part out of the nozzle, the fibers are the most uniform fibers.

Electrospinning is a subjecting of a fluid jet to a high electric field process, by which polymer fibers with nano-scale diameters lower than 100 nm are formed. Significant progress has been made in this area throughout the past few years and this technology has been exploited to a wide range of applications. However, the efficiency is still very low because the repelling force could not be controlled between two needles. For the investigation, two needles were used. And 3 kinds of insulators, including polytetrafluoroethylene (PTFE) tube, polyvinyl chloride resin (PVC) tube and silicon rubber tube, were invited to overcome the repelling force. It is concluded that it is possible to provide a more controllable and easily achieved electrospinning process by using insulators.

In this paper, model of composite insulators were designed to study distortion, movement of the water droplets when discharging occurs on the shed surface of composite insulators applied with uniformity electric field. The distortion and movements of single and multiple water droplets on the surface of insulator in ac and dc electric fields were studied. The results show that the water droplets gradually increase in length in the action of electric field, and the distortion considerably increases with the increase of the electric fields. From these results, the effect of water droplets on flashover voltage is analyzed.

Publisher Summary This chapter presents the influences of annealing method on the space charge properties in low-density polyethylene (LDPE). LDPE films are prepared by three kinds of annealing methods, which are different in cooling velocity. The crystallinity of the LDPE samples are measured and compared. Surfaces of samples are observed. Higher cooling velocity results in lower crystallinity. High DC negative voltage is applied on the samples and then samples are open-circuit. Space charge formed in samples is measured during the above procedure. The space charge properties based on crystallinity and morphology are discussed.

The lightning electromagnetic environments of planned Zhongguancun Software Park near transmission lines, including electrical field, magnetic field and grounding potential rise, are assessed by numerical analysis. From this analysis, we can conclude that the lightning strike is a serious threaten to the software park, protective countermeasures should be adopted to improve the electromagnetic environments of the software park.

The electromagnetic coupling between the control cable with metal shielding sheath and metal conductor of grounding grids in the substation of a power system threatens the safe operation of an electronic system connected with the control cable. In order to simplifying the electromagnetic coupling analysis of this system, the core-sheath model of a control cable is replaced by a parallel multi-conductor model with theoretical analysis and numerical computation in this paper. From analysis of the resistance and the self-inductance of the sheath, the mutual inductance and the capacitance between the core and the sheath in both models, four nonlinear equations to solve the four unknown parameters in the parallel multi-conductors model are established. A program has also been coded to solve the equations. The results of the parallel multi-conductors model are compared with the analyzed ones of the actual control cable by the PSCAD software package. They have good agreement with each other.

The room temperature vulcanizing (RTV) silicone rubber coating on the surface of insulator may increase the flashover voltage of contaminated insulators, which is designed to replace greasing and cleaning of insulators. The RTV silicone rubber coatings have been used in China to prevent pollution flashover of insulators due to their long service life and convenience. The paper presents a review of RTV silicone rubber coatings in China. Present day coatings are the result of nearly sixteen years of development and use. In all but a few dirty environments, these coatings have lasted fifteen or more years without maintenance and where maintenance has been found to be necessary, cleaning is done at a significantly reduced schedule. The paper focuses on the important characteristics of these coatings and on the rigorous attention that is required in their application in order to ensure good performance.

The use of room temperature vulcanized (RTV) silicone rubber (SIR) coatings for improving the contamination performance of existing ceramic insulation has become popular. RTV SIR coatings work on the principle of providing a high surface resistance even in the presence of moisture and contamination, hence, limiting the leakage current to harmless levels. This paper deals with the flashover mechanism and performance of contaminated RTV SIR coated insulators under wet conditions. Four types of profiles of insulators with RTV SIR coating were evaluated. The withstanding voltage and flashover tests were performed on these insulators. The equivalent salt deposit density and the non-soluble deposit density were measured. Based on the analysis of leakage current monitored, the flashover mechanism of RTV SIR coated insulators was proposed in this paper.

The loss of surface hydrophobicity of room temperature vulcanized (RTV) silicone rubber (SIR) due to immersion in acid, alkali and saline solutions has been studied as a function of immersion time and concentration. The loss and recovery of the hydrophobicity is correlated with the solute and the absorption of water during immersion and its subsequent desorption in air. The hydrophobicity is determined by measuring the static contact angle between the tangent to a droplet of distilled water and the horizontal RTV-SIR coating surface. The surface tensions of solutions were measured before and after the RTV-SIR coatings were immersed in solutions. The values show the effect of solution on RTV-SIR coating.

The leakage current of a polluted insulator not only depends on pollution degree and damped situation, but also depends on insulator shape, insulator string length, operation voltage etc. This paper studies the relationship between the leakage current and factors such as the pollution degree, the damped state of contamination, the shape of insulator, the operation voltage, etc. Based on the above research, a method to determine the warning value of leakage current is proposed. >

There is a large area at high altitude in China where it is necessary to build high voltage transmission lines and substations. Studying the discharge characteristics of several important types of electrical field is a very important topic in the development and building of power systems in a high altitude area. In this paper a series of tests have been done in a chamber, in which the air pressure could be changed. The tested models included sphere-sphere gap and point-plane gap. The discharges along dry clean, wet clean and wet polluted surfaces were also studied at different air pressures under both AC and DC voltages. The discharge characteristics of the above models at different pressure air were analysed and discussed. >

The usage of silicone rubber insulators in various contaminated areas has increasesd prominently and still keeps rising. In the case of China, more than 90% of the 800000 composite insulators are operating in heavy or medium pollution environments. As the exposure time in the field is prolonged, the change of hydrophobicity and the build-up of pollution layer directly affect pollution performance of the composite insulator. The paper is based on part of the work of a system investigation aiming at inspection and evaluation on pollution performance and aging of the composite insulator in service. More than 40 composite insulators, all made of HTV silicone rubber, were removed from 110 kV-220 kV HV lines. The service time changes from 1 year to 10 years. Hydrophobicity status and pollution status of these insulators are reviewed in the paper. Data from the field provide important references for the research on aging and pollution property and for the build-up of relevant test methods.

Considering various contaminated environments in the field, research on the hydrophobicity transfer properties of different pollutants is necessary for the proper selection and maintenance of polymeric insulators. In the paper, hydrophobicity of SR polluted by several kinds of pollutants such as kieselguhr, kaolin, Tonoko, metal oxides and inorganic salts were investigated. Contact angle measurement and FTIR analysis have been used to trace the hydrophobicity transfer process. It is found that the inherent chemical properties and the physical morphology of pollutants play important roles on the hydrophobicity transfer property.

Brittle fracture of composite insulators occurred in China makes it a subject concerned by many people, and it is urgently necessary to put forward a test method on the resistant of FRP core against stress corrosion. The brittle fracture caused by stress corrosion is simulated in two similar ways The fracture modes are analyzed, and the measures to improve the stress corrosion resistance are studied. As the results, a modified stress corrosion test method is suggested, and the stress corrosion resistance of FRP rod is improved greatly when E glass fiber is still adopted.

Dielectric barrier discharge in nitrogen at atmospheric pressure is studied with the spectroscopy and the fast photography of the discharge. By the introduction of a nitrogen flow into the discharge gap, the homogeneous discharge in a 2 mm gap can be maintained. Based on the waveform of the discharge current characterized by a current pulse per half cycle of the applied voltage and the 1 μs exposure discharge photograph showing a luminous layer covering the entire surface of the anode, the homogeneous discharge is identified with a Townsend discharge. The instrumental broadening of the spectrometer used in the experiment is calibrated with a helium-neon laser. The data relevant to the instrumental broadening are input into a code called Specair for calculating the spectrum profiles of 0—2 band in the second positive system of nitrogen molecules at different gas temperatures. By fitting the calculated spectrum profiles to the experimental one, the rotational temperature of the nitrogen molecules is determined. The results show that the dielectric barrier Townsend discharge in nitrogen at atmospheric pressure cannot heat the nitrogen to a high temperature (ΔTg≤50 K) and the small rising in temperature does not induce the thermal instability that leads to the transition of the Townsend discharge to a filamentary discharge. By the addition of a gas flow into the discharge gap, the nitrogen is indeed cooled down to a lower temperature. However, it is not the reason for the Townsend discharge to be maintained. By comparing the discharge spectra with and without the gas flow, it could be concluded that the gas flow much reduces the density of the impurity oxygen desorbed from the dielectric by the discharge and makes it possible for more nitrogen metastables to survive to the beginning time of the next discharge and to provide sufficient seed electrons which are necessary for Townsend discharge.

Homogenous discharges were produced in a 2-mm air gap at atmospheric pressure by using 325# fine wire mesh as electrodes covered with 0.1 mm PET films and 50Hz line power source paralleled with a discharge-stabilizing capacitor. For obtaining such a homogeneous discharge it is important to attach tightly the wire mesh together with the PET film on the surface of a Rogowski electrode. The experiments show that the commonly used method to distinguish a homogenous discharge from a non-homogeneous one by the waveforms of discharge current and transferred charge is not always reliable since the waveforms could tell only the discharge simultaneity rather than the discharge homogeneity. A fast image of discharge with an exposure time not longer than 100ns should be used instead to judge the discharge homogeneity. It is the first time in the experiments of atmospheric pressure discharge using wire mesh electrode covered by PET film such fast images were obtained, which indicates that the homogeneous discharge is a Townsend discharge rather than a glow discharge.

In this paper, the pollution regularity versus time and various weather conditions and the distribution of contamination on the surface of a porcelain insulator is discussed in detail using a partial surface conductivity method. The results illustrate that the self-cleaning ability of rain has a notable influence on the contamination of each kind of insulator. Compared with the conventional equivalent salty deposit density method, the partial surface conductivity method is an effective measurement and also a practical one to inspect the contamination density and research into the pollution regularity of the insulator.

The 750 kV alternating voltage of transmission lines plan to be built in the northwest of China, where the altitude is from 1800 m to 2800 m, and the climate is very serious. In the design of the lines, we contrast the ability against the pollution flashover of the post insulators. For three types of typical high intensity, big diameter post insulators, the artificial contamination tests are carried out in four pressure cases corresponding to the altitude from 0 m to 3000 m and in two typical kinds of equivalent salt deposit density (ESDD). The test results show that the flashover voltage of polluted insulators at high altitudes regularly decreases with the dropping of the air pressure. And there is certain relationship between voltage and the shed shape. Also, with a normal post insulator with RTV coating, the artificial contamination tests are carried out in the four pressure cases. The test shows, in the same ESDD and the same pressure condition, the ability to prevent the pollution flashover of the post insulator with RTV coating is much too stronger than that without RTV coating. And the rule that the flashover voltage decreases with the dropping of the air pressure is almost the same.

The conductor-conductor gap is a practical operation parameter in transmission lines. In the past, the insulation distance between conductors was determined only by a simple impulse voltage. But for compact lines, a more precise model of sparkover characteristics should be studied in detail. In this paper, the influence of a pre-stressing AC and floating electrode on the U/sub 50%/ composite sparkover voltage for a conductor-conductor gap is discussed.

Room temperature vulcanized (RTV) silicone rubber (SIR) coatings are used increasingly on outdoor HV porcelain and glass insulators and bushings when subjected to heavy pollution. An important property of the RTV-SIR coating is its ability to restore the hydrophobicity of the surface after a layer of contamination has built up on it, and thus continues to suppress the development of leakage current, dry band arcing and flashover. As hydrophobicity is the key to the superior contamination performance outdoor insulation, the present study was undertaken to better understand this phenomena. In this paper, the hydrophobic migrations of RTV SIR coating with the pollution of kieselgur and kaolin were measured. The virgin kieselgur and kaolin and them with hydrophobicity were analyzed using Scanning Electron Microscope. The theory of absorption and cohesion is introduced and applied to explain the mechanisms of hydrophobic transfer.