Dry Band Research Articles

브리지 특성이 트래킹에 미치는 영향에 관한 연구

본 논문은 전해액에 의해 양전극 사이에 형성되는 브리지가 트래킹에 미치는 영향을 기술하고 있다.BR IEC(International Electrotechnical Commission) 60589의 방법으로 만들어진 1, 3, 5[wt%] NaCl 용액을 이용하여 KS C IEC 60112의 전극에서 트래킹 실험을 하였다. 트래킹 진전과정 중에서 브리지가 형성되었을 때의 전압, 전류, 저항 및 열화상을 측정하여 분석하였다.BR 그 결과 전해액의 전도율이 커짐에 따라 브리지에서 발생되는 줄열도 커졌다. 하지만 전해액의 기화열로 인해 전해액의 끓는점을 넘지는 못했다. 다만, 전해액의 전도율이 커짐에 따라 건조대 형성에 소요되는 시간이 짧아졌다. 따라서 다음 적하까지 보다 긴 시간동안 건조대를 유지함으로써, 방전 기회가 증가하기 때문에 트래킹 진전이 빨라짐을 알 수 있었다.

Nanofilled silicone dielectrics prepared with surfactant for outdoor insulation applications

This paper reports on the heat erosion resistance of various silicone rubber compositions under infrared laser heating that simulates the dry band arcing phenomenon on outdoor insulation. The composites are made using a two-part addition cure silicone rubber, with various amounts of alumina, natural silica, or fumed silica, nano-or micron size, and different amounts of Tritontrade X-100 surfactant. It is shown that the surfactant greatly improves the dispersion of nanosized particles, yielding composites that are more homogeneous, with improved resistance to heat ablation. Significantly improved dispersion in the presence of surfactant is confirmed by SEM analysis for some nanofillers, while very little effect is observed for others. The surfactant is beneficial up to the point where the filler surface is saturated with the additive. Fumed silica is shown to impart greater heat ablation resistance than natural silica and alumina. Furthermore, a distinct protection mechanism appears to be operative for fumed silica and natural silica as opposed to alumina.

Effect of insulator profile on aging performance of silicone rubber insulators in salt-fog

The paper presents the results of the study on the influence of insulator profile on the aging performance of silicone rubber (SIR) insulators in salt-fog. Experiments have been conducted on various two-shed arrangements at 35 V/mm average stress and 0.25 S/m salt-fog conductivity level. The work is also extended to include commercial 15 kV class insulators with different profiles. Shed spacing, shed diameter, alternate shed design and shed shape are the parameters investigated in this study. The low frequency harmonics of the leakage current, early aging period (EAP), and equivalent salt deposit density (ESDD), are used to evaluate the aging performance of different designs. Insulator profile is shown to greatly influence the aging performance of SIR insulators. Shed shape proves to be the most important parameter to be considered in designing non-ceramic insulators profiles. Also, as the shed spacing decreases, the performance of SIR insulators improves. Simulation results using FEMLAB show that the electric field on insulators is below the corona onset at both dry and wet conditions. Dry band arcing is therefore the main electrical cause for aging in distribution class insulators and it is possible to improve the pollution performance of SIR insulators using appropriate profiles as suggested in this work

Inferring ceramic insulator pollution by an innovative approach resorting to PD detection

This paper presents a technique for outdoor ceramic insulator pollution assessment based on partial discharge detection and analysis. Laboratory tests and data coming from a monitoring activity carried out on some insulators of transmission lines are reported. They support the effectiveness of partial discharge detection and analysis as a tool to carry out condition-based maintenance of insulators of overhead lines. In particular, it can be seen that partial discharge analysis highlights the mechanisms bringing insulators to flashover (dry band arc activity) and is, therefore, well suited to predict increasing pollution and imminent flashover. As a consequence, algorithms are proposed to provide a quantitative evaluation of pollution severity

Concentrated Discharges and Dry Bands on Polluted Outdoor Insulators

This paper describes concentrated discharges on polluted insulators in the laboratory and in the field. The authors have observed the concentrated discharges at the high-voltage laboratories in Stuttgart, Zittau, and Mannheim, Germany, and Wroclaw, Poland. The concentrated discharges were also documented under natural conditions. These discharges are very dangerous especially for high-voltage apparatus, bushings, and polymer insulators. It has been shown that due to uneven voltage distribution at very low surface conductivity, the concentrated discharges can ignite even under uniformly polluted and uniformly wetted insulators

Study on hydrophobicity transfer of RTV coatings based on a modification of absorption and cohesion theory

Room temperature vulcanized (RTV) silicone rubber coatings are used increasingly on outdoor high voltage (HV) insulators subjected to heavy pollution. An important property of the RTV coatings is the ability to restore the surface hydrophobicity after a pollutant layer has built up on the surface, which can suppress the development of leakage currents, dry band arcing and flashover. The present study analyzes the hydrophobicity and the hydrophobicity transfer of RTV coatings and the factors that affected the hydrophobicity. A modification of absorption and cohesion theory was used to analyze the hydrophobicity transfer mechanisms and the influences of temperature, polydimethylsiloxane (PDMS) molecular weight, degree of cross-linking, extent of soluble and non-soluble components, and the pollutant properties. The hydrophobicity transfer of RTV coatings was also investigated with various conditions of contaminations and various factors, which affect the hydrophobicity transfer, including the composition of RTV coatings and the outside conditions. Results show that the hydrophobicity transfer of RTV coatings is not only dependent on compositions but also on factors of circumstance. The analysis also explains the obvious difference between the hydrophobicity transfer of RTV coatings to kieselguhr and kaolin based on a particle and surface analysis using the Brunauer, Emmett and Teller (BET) method, which explains the relationship between a BET surface area and the hydrophobicity transfer of the RTV coatings

Leakage Current Waveforms of Outdoor Polymeric Insulators and Possibility of Application for Diagnostics of Insulator Conditions

This paper reports the investigation results on the leakage currents (LC) on polymeric outdoor insulators. The samples used were EPDM (ethylene prophylene diene monomer) insulators used at 20 kV distribution lines. AC voltage was applied and the LC waveforms were measured under various environmental conditions (humidity and pollution). Digital data of the LC was transferred from a digital storage oscilloscope to a computer for further analysis. The LC waveform parameters such as magnitude and harmonic content (as indicated by the total harmonic distortion (THD)) were analyzed. The experimental results showed that 3rd, 5th and 7th harmonics and higher odd harmonics were observed for symmetrical-distorted LC waveforms while for unsymmetrical-distorted LC waveforms, odd and even harmonics were observed. The LC analysis indicated that there are 5 stages of insulator conditions from normal condition up to flashover correlated with different kind of LC waveforms. The results also showed that in general the magnitude of LC was good enough to show the condition of the insulators. However, under discharge condition (for example as a result of dry band arching) the LC magnitude should be combined by the THD to show a better correlation with the insulator condition. The product between THD and LC magnitude may be used as a diagnostic parameter.

Experimental Verification of the Proposed IEEE Performance and Testing Standard for ADSS Fiber Optic Cable for Use on Electric Utility Power Lines

All Dielectric Self Supporting (ADSS) fiber-optic cable jackets are subject to dry band arcing associated with wet, conductive pollution, quantified electrically by ohms per meter, in conjunction with the location of the ADSS in relation to conductor placement on high-voltage transmission structures. In order to determine the suitability of a particular ADSS jacket material to resist dry band arc damage in various levels of pollution as well as for incipient voltage levels, an electrical test, employing equivalency to the dry band environment, has been proposed. A set of desirable hypothetical results are briefly discussed. The tests results described herein, for common polyethylene jacketed ADSS, support the nature of the hypothetical data. It is noted that this is not "pass-fail" but a test that establishes performance criteria. It has been submitted to the fiber optics standards working group.

Potential and electric-field calculation along an ice-covered composite insulator with finite-element method

A two-dimensional finite-element model for potential and electrical-field calculation along an ice-covered composite insulator is presented. To find the influence of the ice on the potential and electrical-field distribution, various thicknesses of the ice and various lengths of the icicles are simulated in the condition of dry ice and wet ice, respectively. In addition, the present study investigates the influence of the discrete water film and the dry band on the potential and electrical-field distribution of the iced composite insulator. Finally, a comparison between the electric-field distribution along the ice-covered composite insulator and that of ice-covered ceramic insulator string is presented.

Silicone rubber dielectrics modified by inorganic fillers for outdoor high voltage insulation applications

The paper discusses the mechanisms by which inorganic fillers in silicone rubber dielectrics enhance the properties of thermal conductivity, relative permittivity, and electrical conductivity making them useful in outdoor high voltage insulation applications. The addition of alumina trihydrate or silica fillers to silicone elastomers, forming binary composites with enhanced thermal conductivity, is discussed in relation to filler type, particle size, shape, and concentration, and its use as a housing material for non-ceramic insulators to minimize material erosion at dry band arcing sites by lowering hot spot temperature. Also discussed is the enhanced relative permittivity of silicone dielectrics that is obtained through the addition of barium titanate powder which can be further increased with the addition of aluminium powder forming a tertiary composite, resulting in a significant grading of the surface electric field when applied as a housing material to high voltage bushings. Controlled electrical conductivity of silicone dielectrics is discussed through the use of antimony-doped tin oxide filler binary composites and when applied as a housing material to outdoor bushings, the pollution performance is greatly enhanced.

Novel technique to evaluate the erosion resistance of silicone rubber composites for high voltage outdoor insulation using infrared laser erosion

The standard methods available to test tracking and erosion resistance of filled silicone rubber do not allow to delineate the fundamentals of the thermal degradation, although the heat from the dry band arcing is the main degradation factor. In this work a thermal imaging camera is used to investigate the performance of filled silicone rubber in an inclined plane test, and a scheme is established to relate the temperature and the electrical discharge energy. Further, an infrared laser technique, based on constant energy approach, is developed to study the material performance under laser heating. The technique consists of applying a certain amount of infrared laser energy during a set time period, in order to produce erosion in the silicone rubber samples. Through correlation studies the applicability of the proposed laser technique to rank silicone rubber samples with various fillers has been validated. The laser tests show identical ranking of samples when compared to samples ranked using inclined plane tests, yet offering significant advantages of being faster, simpler, and reproducible.

Suppression effect of ATH filler on the erosion of filled silicone rubber exposed to dry band arc discharge

This paper describes the results of experiments made to examine the suppression effect of alumina trihydrate (ATH) filler on the erosion of filled silicone rubber(SR) exposed to dry band arc discharge. In this study, one simulated electrolyte electrode system was used to generate the dry band arc discharge and the eroded mass of SR filled with 0–50 wt% ATH was measured. Thermogravimetric differential thermal analysis (TG-DTA) was applied to study the thermal characteristics of filled SR and clarify the suppression mechanism of ATH on the heat erosion. In addition, physicochemical analyses on the degraded specimens were carried out by using the techniques of Fourier transformed infra-red (FT-IR) spectroscopy and scanning electron microscopy (SEM) after the heat treatment caused by arc discharge. It is demonstrated that the erosion of filled SR due to dry band arc discharge can be well suppressed through the dehydration of ATH filler and the depression effect of ATH filler on erosion can be improved with increase of filler content.

Study on development of dry band on ADSS fiber optic cable

All dielectric self supporting (ADSS) fiber optic cables are suffering from damage caused by dry-band arcing. This paper investigates the formation of the dry band, which is crucial to the arcing. The formation of the dry band is the result of evaporation of water deposit some point on the cable surface. When the dry band is formed the current is interrupted. Then high voltage is applied to the small gap separated by the dry band, and may cause arcing. This paper discusses the drying process of the wet layer on the surface of the cable in detail. The differential equation of the drying rate is formulated and numerical simulation is performed. With this equation, the time-to-arcing and variation of the layer resistance can be estimated. For verification of the results, the time-to-arcing and layer resistance are measured in the laboratory. The numerical results provide guidance for design of an automatic dry-band arcing aging test system. The onset of arcing is investigated based on the results.

Mechanism for change in leakage current waveform on a wet silicone rubber surface-a study using a dynamic 3-D model

This paper describes the results of experiments and simulations made to examine the waveform of leakage current flowing through the surface of HTV (high temperature vulcanized) silicone rubber specimen exposed to clean fog. Water droplets were placed on the surface of specimen energized with AC voltage and investigations of the surface state were done by a high-speed video camera in a wet condition produced by sprayed clean fog. Simultaneously, according to the experimental condition, a dynamic 3-D model was built to calculate the electric field and current density distribution on the specimen surface by a finite element software. A conducting water layer is formed due to the deformation of droplets and the development of dry band arcing. This caused large distortion and nonlinearly which increased the odd harmonic components in the leakage current waveform. This is in good agreement with the simulating calculation. The information from the leakage current frequency characteristic was extracted and correlated with the insulation surface condition. It can be considered as a diagnostic index for electrical characteristics and insulation state of polymer insulators in the wet condition.

Infrasonic tonal resonances of tropical hurricanes

In news pictures saturating the media last summer there is contained subtle but compelling evidence that tropical hurricanes emit intense and extremely low-frequency tones, originating in the eye. The excellent symmetry of a well-formed eye predisposes the central cavity of a hurricane to resonate in the normal modes of a low-Q nearly cylindrical chamber, due to the slight mismatch in sound speed at the eye wall. Second order perturbation analysis of interaction between eye-modes and steady wind corkscrewing up through the eye has confirmed that positive feedback is generated, the condition for self-excited oscillation. Dimensions and speed of typical hurricanes require that the tones have frequencies on the order of 1/100 of 1 Hz, which is doubtless the reason why they have escaped previous detection. Visual evidence appears in multiple alternating rain and dry bands that originate around the inner circumference of the eye wall, observable in aerial photos by NOAA. These are most easily explained as due to intense acoustically-driven temperature oscillations about the dew point, inside the eye. For a given hurricane, the actual tonal frequencies can be deduced from the spacing of these startups.

계면활성제가 첨가된 염수용액에 따른 폴리머 애자의 트래킹 성능 평가

Recently, polymer insulators that are used for high voltage applications have some advantages such as light weight, small size, vandalism resistance, hydrophobicity and easy making process. During outdoor service of polymer insulators, the surface of the insulating material is frequently subjected to moisture and contamination that lead to dry band arcing. Their tracking resistance, erosion resistance, end sealing and shed design are very important because dry band arcing causes degradation of polymer surface. Aging test to estimate life property of polymer insulator is executed through several international standard such as IEC 61109 and CEA tracking wheel test, but is not getting clear conclusion yet. There are two methods in the diagnosis method of polymer insulator such as off-line and on-line. The diagnosis methods in off-line are external condition analysis by the eye, contaminant analysis on surface, surface analysis, pollution withstand voltage test, power frequency flashover voltage test, lightning impulse flashover test, tensile fracture load test and flexural load test. Polymer material is also investigated it`s tracking resistance by adding surface active agent in IEC 587. In this paper, the tracking performance of polymer insulator with salt solution which is added surface active agent. The diagnosis of insulator sample has been analyzed by leakage current and visual examination, STRI guide and thermal image camera.

A model for high voltage polluted insulators suffering arcs and partial discharges

In this paper, we propose a simulation model for contaminated insulators. The theoretical analysis of the proposed model is provided, together with the mathematical analysis of the related equivalent circuit and a mathematical function that simulates the behaviour of the dry band resistance as a function of time, even in cases where arcs or partial discharges occur. To specify the model’s parameters and the dry band resistance function, a series of measurements of the applied voltage and leakage current of 20 kV porcelain insulators was performed. After determining the required parameters, a test was performed to evaluate the accuracy of the behaviour of the model compared with that of the active insulator. In practice, the proposed model seems to satisfactorily simulate the behaviour of the contaminated insulators.

Experimental Studies of the Characteristics of Dry Band Arcing on ADSS Fiber Optic Cables

A series of simulated arcing experiments are conducted in a laboratory setting to investigate the characteristics of dry band arcs on ADSS fiber optic cables. The measurement of resistance, power, and energy of dry band arcs is described. The impact of voltage and current on arc resistance is presented. The power and energy of dry band arcing is measured under different short-circuit current and open-circuit voltage. An equation which relates arc power to open-circuit voltage and short-circuit current is proposed. Experiments show that arc power has a threshold to cause the damage of cable jackets. The study of arc power and energy can be used to predict a potential damage of ADSS cables.

A Study on Erosion Resistant Characteristics of ATH-filled Silicone Rubber Exposed to Dry Band Arc Discharge

A Study on Erosion Resistant Characteristics of ATH-filled Silicone Rubber Exposed to Dry Band Arc Discharge

Thermal conductivity of filled silicone rubber and its relationship to erosion resistance in the inclined plane test

Silicone rubber samples having various concentrations and mean particle sizes of either alumina tri-hydrate or silica filters, prepared by room temperature and heat cured under pressure (hot pressed), are tested for erosion resistance in the ASTM D2303 inclined plane tracking and erosion test. Their corresponding thermal conductivities are determined using a transient temperature technique in which an infrared laser is employed as the heat source and a thermal imaging camera as a temperature detection device. Scanning electron microscope observations show greater filler bonding to the silicone matrix in the hot pressed samples than in the room temperature vulcanized samples leading higher thermal conductivity and increased resistance to erosion, for both ATH and silica filled samples. The correlation study shows a strong relationship between the erosion resistance and the thermal conductivity of the tested samples, highlighting the importance of an outdoor insulating material to have high thermal conductivity in order to withstand dry band arcing. The results can be used to provide guidance on filler selection for silicone rubber compounding for outdoor insulation applications.