Transmission Line Insulators Research Articles

Experimental techniques to simulate naturally polluted high voltage transmission line insulators

This paper represents experimental techniques to simulate the naturally polluted high voltage insulators, under conditions that simulate the desert environment. Usually, the IEC fog method is used for testing the polluted insulators of high voltage transmission lines, but it does not simulate them under the desert pollution environments. For that reason, in this paper two other suggested techniques are added to the IEC one. The first one is to explain the performance of the polluted insulators under the dew and the second one is to explain their performance under the simultaneous fog and dew. The results of these three tests are compared with each other under different surface polluted layer conductivities. The aim of this paper is to record the leakage current and the warning voltage under different simulation weather conditions that to monitor the insulator strings before the occurrence of the flashover that of course is useful for the efficient maintenance. Also, in this paper, an attempt to simulate the flashover of the insulator in the field condition (actual outdoor condition) is presented. Where, the surface of the insulator is polluted naturally over a relatively long period, while it is permanently under high voltage.

Surface charge accumulation and decay of direct-fluorinated RTV silicone rubber

Silicone rubber (SiR), as a basic insulating material, is widely used in insulators for HVDC transmission lines. In these lines, corona discharge even occurs on well-designed hardware and insulators, which can inject charge into the insulator surface. The existence of surface charge has a marked effect on insulation degradation and plays an important role during the development of the surface flashover. Direct-fluorination is a method to change the chemical component, which could induce the corresponding changes in electrical properties of the surface layer, thus influencing the charge injection. This paper tries to study the effect of fluorination time on surface charge accumulation and decay of room temperature vulcanized (RTV) SiR. The samples were fluorinated in a laboratory vessel at 298 K (25°C) using a F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixture with 12% F2 by volume at 0.05 MPa (500 mbar) for 5, 10, 15, and 20 minutes. The sample surface chemical composition was analyzed by means of ATR-IR. The behavior of surface potential under dc voltage was recorded at room temperature with a relative humidity of ~40%. Obtained results show a dependence of the surface potential and the dissipation time upon the fluorination time, varying with the charging time. It is suggested that the direct fluorination can significantly suppress the accumulation and accelerate the decay of the surface charge.

Characteristics of Secondary AC Arc Column Motion Near Power Transmission-Line Insulator String

Power system secondary ac arcs are plasma discharges in free space with dimensions in meters. The motion of secondary arcs was investigated experimentally using high-speed video on a 1-m scale with a 3-MVA source. The measurements that were evaluated imposed forces, including wind, effects of the arc root, as well as early-stage horizontal and late-stage vertical movement. Partial short circuits of the arc column were observed. The arc column elongated with the de-ionization effect being increased. The column approached a maximum length before the arc extinction. An arc chain model was applied to establish the governing velocity equation. Based on the proposed model, simulations agreed well with the physical experiments.

Prediction of Flashover and Pollution Severity of High Voltage Transmission Line Insulators Using Wavelet Transform and Fuzzy C-Means Approach

Major problem in the high voltage power transmission line is the flashover due to polluted ceramic insulators which leads to failure of equipments, catastrophic fires and power outages. This paper deals with the development of a better diagnostic tool to predict the flashover and pollution severity of power transmission line insulators based on the wavelet transform and fuzzy c-means clustering approach. In this work, laboratory experiments were carried out on power transmission line porcelain insulators under AC voltages at different pollution conditions and corresponding leakage current patterns were measured. Discrete wavelet transform technique is employed to extract important features of leakage current signals. Variation of leakage current magnitude and distortion ratio at different pollution levels were analyzed. Fuzzy c-means algorithm is used to cluster the extracted features of the leakage current data. Test results clearly show that the flashover and pollution severity of power transmission line insulators can be effectively realized through fuzzy clustering technique and it will be useful to carry out preventive maintenance work.

Contribution of Design Parameters of SiR Insulators to Their DC Pollution Flashover Performance

Compared to HVAC, the application experience of composite/polymer insulators in HVDC transmission lines is limited. However, the tendency to utilize them in HVDC transmission lines, where pollution flashover is a major problem, is growing due to their water-repellent feature. This trend demands understanding insulator flashover performance and recognizing key parameters in the design and dimensioning of insulators. This paper presents the measurement and analytical results for dc pollution flashover of silicon rubber insulators at extra heavy pollution conditions. Two approaches are employed to model flashover voltage gradient and quantify the contribution of salt deposit density, specific leakage distance, average diameter, shed spacing to shed depth ratio, and form factor to insulator pollution performance. Developing a nonlinear regression model, the effect of the mentioned parameters on pollution flashover is studied. Then, the artificial neural network (ANN) and randomization method are used to develop a model to interpret parameters contribution to pollution flashover, and the results are validated with those of the regression method. Finally, by applying an ANN-based randomization approach, a multi-input model is created to quantify the significance of different parameters in flashover voltage gradient. The model ranks specific leakage distance and average diameter, respectively, as the most and least important geometrical characteristics in pollution flashover performance of SiR insulators. The method and results can be a source of information to optimize the design and dimensioning of HVDC SiR insulators especially in severe pollution conditions.

Flashover Prediction of Polymeric Insulators Using PD Signal Time-Frequency Analysis and BPA Neural Network Technique

Flashover of power transmission line insulators is a major threat to the reliable operation of power system. This paper deals with the flashover prediction of polymeric insulators used in power transmission line applications using the novel condition monitoring technique developed by PD signal time-frequency map and neural network technique. Laboratory experiments on polymeric insulators were carried out as per IEC 60507 under AC voltage, at different humidity and contamination levels using NaCl as a contaminant. Partial discharge signals were acquired using advanced ultra wide band detection system. Salient features from the Time-Frequency map and PRPD pattern at different pollution levels were extracted. The flashover prediction of polymeric insulators was automated using artificial neural network (ANN) with back propagation algorithm (BPA). From the results, it can be speculated that PD signal feature extraction along with back propagation classification is a well suited technique to predict flashover of polymeric insulators.

Transmission Line Insulators Detection Based on KAZE Algorithm

Transmission Line obstacle detection technology is one of the hot spots of computer vision and transmission line inspection robot system.As the most common obstacle of inspection robot,correctly identify of insulators can help improve the reliability and accuracy of self-inspection. Low robustness of traditional detection algorithm can not meet the requirements on insulators detection when dealing with complex environment. To solve the above problem, a transmission line insulators detection method based on KAZE algorithm is given. The feature extraction is done in the nonlinear scale space, and feature vectors are formed with M-SURF algorithm, what’s more, feature vectors detecting is worked through the nearest neighbor algorithm as matching criteria and RANSC generated algorithm. Experimental results show that the effect of insulators detection algorithm based on KAZE detect faster and also make a good performance on accuracy and robustness.

Long front time switching impulse tests of long air gap in UHV projects at altitude of 2100 m

The past and recent investigations show that front time of switching overvoltage waveforms in Ultra High Voltage (UHV) system of long distance transmission are mostly in long wave front time exceeding 1000μs. The long front time of switching impulse voltage has been deviated from the critical front time. This paper is involved with breakdown characteristics and external insulation design under long front switching impulse voltage in UHV system. All the Tests were performed on an outdoor UHV test site at altitude of 2100 m, China Southern Power Grid Co. Ltd. (CSG). Breakdown characteristics of rod-plane and actual size tower-conductor in /spl l.chemo/800 kV UHV DC transmission line are obtained under wide front time switching impulse voltages from 100 to 2350 μs. From the comprehensive studies of such tests, it is proposed that U50 of front time exceeding 1000 μs increases 20% compared with the results of standard switching impulse (250/2500 μs) tests and standard deviations of U50 is 6% in UHV transmission system. Finally, an air gap insulation design procedure in conductor-tower of UHV transmission line at altitude of 0-2000 m is presented. Long front time switching impulse strength of conductor-tower gap is proposed into selection by reference in UHV transmission line insulation design.

Pollution performance of HVDC SiR insulators at extra heavy pollution conditions

As an integral part of transmission lines, insulators play a major role in the reliability of power systems and their failure exposes the performance of the whole system into risk. Compared to AC systems, DC static field and corresponding arc without zero crossing makes DC flashover performance more problematic. Although the utilization of composite insulators in HVDC transmission lines continues to grow, there is still a lack of investigation on DC pollution flashover performance of SiR insulators especially at extra heavy pollution conditions. This paper presents the measurement and analytical results for DC flashover of SiR insulators in terms of different polarities of voltage, hydrophobicity levels and geometrical characteristics of SiR insulator at extra heavy pollution conditions. According to the results flashover strength in positive voltage is 4% higher than that in negative voltage. In addition, different profiles of SiR insulators did not show the same pollution flashover sensitivity on hydrophobicity. The empirical modeling of pollution flashover performance of insulators in terms of specific leakage distance, average diameter, form factor and the ratio of shed spacing to shed depth, revealed that specific leakage has the highest impact on pollution-flashover voltage gradient. This is of importance especially for designing and dimensioning of SiR insulators to be used under HVDC voltage.

Laboratory simulation of naturally polluted high‐voltage transmission line insulators

This study represents experimental techniques for testing the high-voltage polluted insulators under conditions simulating the natural environment. International Electrotechnical Commission (IEC) fog method is used for testing the insulators of type π-ϕ-E4.5, but it does not simulate the desert pollution environments. For that reason, other two suggested techniques are added to explain the performance of the polluted insulators under dew and under simultaneous fog and dew, respectively. The leakage current bursts are recorded in each test type. Also the effect of the wetting method of the insulators under testing on the flashover voltage is investigated. The results of the three types of tests are compared with each other, under different surface layer conductivities. It is concluded that the analysis of leakage current bursts can be used to monitor the severity of pollution on the electrical network.

Potential and Electric Field Distribution of 220kV Insulator String with a Faulty Insulator under Windage Yaw Condition

Faulty insulators could appear in the HV transmission line insulator string under the comprehensive effect of electrical, mechanical and environmental factors and they can be detected according to the space potential and electric field distribution variation characteristics around the insulator string. Finite Element Method (FEM) was used to study the potential and electric field distributions of a 220kV suspension insulator string contained a zero-value insulator in windage condition, comparing with a fine insulator string. The results show that the variation of the space potential and electric field distributions of insulator string is the same as that under no windage condition. The curve of synthetic electric field along the central axis around the good insulator string is U-shape. The 10th and 11th insulators from the high-voltage end are the sensitive insulators where the distortion ratio of synthetic field strength is higher than 3%, when a faulty insulator is in the string. This result can provide preferences for the online detection of faulty insulators.

Comparison on ac icing flashover performance of porcelain, glass, and composite insulators

The electrical performance of insulators under the comprehensive conditions of low air pressure, pollution and icing, is an important basis for the selection of external insulation of transmission lines and substations in icing regions. However, little research has been dedicated to the comparison on ac icing flashover performance of composite, porcelain and glass insulators in this environment. Based on the investigations carried out in the artificial climate chamber on three types of iced insulators, the ac flashover performances of insulators were researched in this paper. In addition, the paper analyzed and compared the effects of various factors, including ice thickness, pollution and air pressure on the flashover performance of three types of iced insulators. The experimental results show that the flashover voltage of three types of insulators decreased with the increase of ice thickness, pollution, and the altitude. The characteristic exponent characterizing the influence of the ice thickness, pollution and atmospheric pressure on the flashover voltage were related with the insulator types. The effect of ice thickness and atmospheric pressure on icing flashover voltage was more apparent for composite insulator than porcelain and glass insulator. The characteristic exponent characterizing the influence of pollution on the flashover voltage was small for composite insulators. Under the same condition, the flashover voltage gradients of ice-covered composite insulators are slightly greater than porcelain and glass insulators.

Silicone insulators of power transmission lines with a variable inorganic load concentration: Electrical and physiochemical analyses

Polymeric insulation is an increasing tendency in projects and maintenance of electrical networks for power distribution and transmission. Electrical power devices (e.g., insulators and surge arresters) developed by using polymeric insulation presents many advantages compared to the prior power components using ceramic insulation, such as: a better performance under high pollution environment; high hydrophobicity; high resistance to mechanical, electrical and chemical stresses. The practice with silicone insulators in polluted environments has shown that the ideal performance is directly related to insulator design and polymer formulation. One of the most common misunderstandings in the design of silicone compounds for insulators is the amount of inorganic load used in their formulation. This paper attempts to clarify how the variation of the inorganic load amount affects physicochemical characteristics of different silicone compounds. The physicochemical evaluation is performed from several measurements, such as: density, hardness, elongation, tensile strength. In addition, the evaluation of the physicochemical structure is carried out using infrared test and scanning electronic microscopy (SEM). The electrical analysis is performed from the electric tracking wheel and erosion test, in agreement with the recommendation of the International Electrotechnical Commission (IEC).

Artificial Neural Network Assisted Digital Image Processing to Determine the Hydrophobicity of Polymeric Materials

Hydrophobicity of polymeric insulators of high power transmission line is an important property because it is a good monitor of aging of polymeric outdoor insulator. An employee on the high-voltage transmission line makes this procedure during operation, which can lead to injuries and incorrect estimation of the insulator integrity. In this way, digital image processing is a promising and objective tool to analyze the polymer surface. In this study, two thousand pictures were taken from the wetted insulator surface and analyzed by artificial neural network assisted digital image processing. The neural network used is based on back-propagation method, and Haralicks descriptors were used to quantify the hydrophobic aspect of various polymeric aged surfaces.

电网舞动区域分布图自动绘制方法与应用研究

本研究以国家电网《舞动区域分级标准与舞动分布图绘制规则》为依据，将舞动区域分布图的绘制算法和流程采用计算建模来自动实现，并分析了舞动区域分布图在指导输电线路绝缘子选型和差异化防舞设计与改造中的具体应用，为输电线路绝缘子的选型提供参考依据，对实现差异化的防舞设计与改造具有重要的指导作用。 In this study, based on the State Grid Galloping Regional Grading Standards and Dancing Plotting Rule, the galloping regional distribution map algorithm and the process are automatically implemented using calculate model, and the regional distribution of the specific application of anti-galloping design and renovation of dance in the guidance of transmission line insulator selection and differentiation are analyzed, providing the reference for the selection of transmission line insulator and playing an important role in guiding the anti-galloping design and transformation to realize differentiation.

Comparative study on field collected samples of aged silicon rubber composite coatings for high voltage insulators

Abstract : Pollution of high voltage (HV) insulators is a phenomenon with a considerable impact to the performance of transmission and distribution electrical networks. The use of composite materials and especially Silicone Rubber proved to be an efficient improvement, capable of suppressing the problem and diminishing the flashover probability. As a result ceramic insulators in transmission lines are replaced by insulators with composite housing, either HTV Silicone Rubber or LSR. In the case of HV substations however, the replacement of insulators is rather difficult, due to the complexity of the equipment and the corresponding financial cost. In this case the application of RTV Silicone Rubber is an equivalent alternative. The ceramic insulators are covered with a 0.5 mm RTV SIR coating which provides the advantages of composite insulators on a ceramic substrate. After installation the possible material lifetime, which is determined by the service conditions and the material formulation, is of primary concern. In Crete, a large scale application exists and coatings that exceed a service period of 10 years are still in operation. The present study focuses on the structural and morphological characterization of field collected composite insulators of various ages so that the degradation degree can be correlated with their service.

Lightning Impulse Corona Characteristic of 1000-kV UHV Transmission Lines and Its Influences on Lightning Overvoltage Analysis Results

The lightning overvoltage is one of key issues in designing the insulation of transmission line and power apparatus. Usually the influence of the impulse corona is ignored in numerical analysis of electromagnetic transients in power systems due to the lack of experimental data. But the relationship between the overvoltage and the insulation size of 1000-kV ac ultra-high voltage (UHV) power systems enters the nonlinear region, and a small decrease in overvoltage will lead to a high reduction in insulation size and bring huge economical benefits. So fully understanding the corona characteristics of the 1000-kV UHV transmission line is helpful to understand the actual wave process and realize a suitable insulation design of the 1000-kV UHV system. Experiments on the lightning impulse corona characteristic of bundle conductors for 1000-kV transmission lines are carried out in the China UHV ac test base and the impulse corona Q-V curves of different bundle conductors are obtained. The results show that the impulse corona leads the increment of the capacitance of the conductor. Analysis on the Q-V curves shows that the occurrence of the positive impulse corona has a time delay after the lightning impulse voltage exceeds the corona inception voltage and the delay time is a tenth of a microsecond. At the end of this paper, a simulation model for corona based on the empirical formulas of Q-V curves fitted from the test results is proposed, and is applied to the overvoltage analysis of 1000- kV transmission line and substation. The analysis results show the lightning impulse corona has a large influence on the lightning overvoltage of the transmission line and substation.

Comparison of External Insulation Level between AC and DC Overhead Transmission Lines

It is important to choose suitable insulator strings that matching the voltage level when trying to change an AC transmission line into a DC one. Historically based, most published works discuss the way of determining the number or the length of insulators for overhead transmission lines, which mainly consider about voltage levels, pollution classes, insulator types and their pollution performances. It calls for too much work for a line restructuring project. In order to simplify the work, a comparison of the choosing of insulator strings between AC and DC overhead transmission line is made in this paper. Two main results are obtained. One is that the ratio, which defined as α, of the number of insulator on DC transmission line and that on AC transmission line ranges from 1 to 2.5 with the decreasing of voltage level under the same pollution class, the other is that the value α remains substantially constant under the same voltage level, and it will decrease slightly as the pollution class increases. The results provide theoretical basis for the choosing of insulator strings in line restructuring projects.

Effect of sputtering gas on structural, optical and hydrophobic properties of DC-sputtered hafnium oxide thin films

The outdoor ceramic insulators of power transmission lines and transformers are suffering from the problem of contamination due to which surface flashover phenomenon is frequent. The main objective of this work was to prepare hydrophobic hafnium oxide (HfO2) thin films to mitigate contamination problem. The hafnium oxide coatings were deposited on glass substrates by DC reactive magnetron sputtering from a pure hafnium target. The depositions of HfO2 films were carried out in O2+Ar and O2+He atmosphere. The structural, optical and hydrophobic properties were examined by varying O2/Inert gas ratio. The prepared samples were characterized by X-ray diffraction, EDS, AFM, UV–vis-NIR spectrophotometer and contact angle goniometer. The coatings were found to be crystalline, transparent and hydrophobic for all samples. The deposition rate, hydrophobicity, transparency, band gap and particle size are better for the films deposited in argon atmosphere in comparison to helium. The hydrophobicity was found to be dependent on roughness of the film. The roughness (5.06nm) and the water contact angle (102.25°) were found maximum for the film deposited at O2/Ar ratio equals to 0.5. The transmittance was also found ~90% at this particular ratio. The band gap of the film deposited at above mentioned ratio was found to be 5.41eV ensuring insulating nature of the film.

RTV silicone rubber pre-coated ceramic insulators for transmission lines

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.