Equivalent Salt Deposit Density Research Articles

Wavelet-Based Flashover Prediction Using High-Frequency Components

Abstract - In order to monitor operating performance of contaminated outdoor insulators, a wavelet-based flashover prediction method is proposed. In most cases, the low-frequency components, namely, fundamental, 3 rd , and 5 th harmonic components have been mainly used for the sake of the spectral analysis of the leakage current. However, in this paper, the detail coefficients of wavelet transform representing high-frequency components are used as important information to predict a flashover in the contaminated insulator. Experimental results verify that the proposed method has a superior capability for flashover prediction.Key Words : Flashover Prediction, Contaminated Insulator, Leakage Current, Wavelet Transform, High-Frequency Components*정 회 원 : Kyungpook National University, School of Electrical Engineering and Computer ScienceE-mail : songyc03@ee.knu.ac.kr접수일자 : 2010년 1월 27일 최종완료 : 2010년 3월 3일 1. Introduction With increasing application in wet and contaminated conditions, such as salt-fog environments, outdoor insulators are exposed to long-term humidity and severe contamination. Once the moisture on the insulator surface is condensed to form continuous wet film, leakage current will be driven by source voltage to pass through the conductive layer. Thermal energy produced by the current cause evaporation of the layer and formation of dry-band gaps. Once the electric field at these gaps reaches the breakdown strength of air, dry-band discharges will occur. Due to initiation and development of the discharges, flashover may take place and affect operating reliability of power systems. From the viewpoint of reducing costs and minimizing risk of damage to people Camcorderand property, it is urgent to develop methods for monitoring outdoor insulator performance in contaminated environments. Current methods include the equivalent salt deposit density (ESDD), optical measurements, and leakage current measurements. In particular, the leakage current can provide much useful information on the state of a contaminated insulators, thus, several approaches using the leakage current have already been introduced to monitor the contamination conditions of outdoor insulators, for example, deterioration pattern analysis, leakage current property comparison under various circumstances, spectral analyses, and stochastic analysis using a Hilbert transform and the level crossing rate [1-6]. However, in most case, the low-frequency components, namely, fundamental, 3

Study of AC Pollution Flashover Performance of Porcelain Insulators at High Altitude Sites of 2800 $\sim$ 4500 m

The external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. However, a few investigations at the high altitude sites of 3000 m and above have been conducted. This paper reports on the laboratory tests of artificially polluted cap-and-pin porcelain insulators performed at the high altitudes of 2800 m to 4500 m. The test results and analysis show that the pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.29 and the one characterizing the influence of nonsoluble deposit density is 0.09 to 0.15. The ac pollution flashover voltage <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> will decrease with the decrease of air pressure <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> and increase with the decrease of ambient temperature <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> . <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> is a power function of the ration of air pressure <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and also is a power function of the ambient temperature coefficient (1 + 0.02( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> - 20)). The average exponent characterizing the influence of air pressure is about 0.56 and the exponent characterizing the influence of ambient temperature is about 0.21 for the three types of insulators in the paper.

Adaptive-Network-Based Fuzzy Inference System Application to Estimate the Flashover Voltage on Insulator

This paper presents application of adaptive network based fuzzy inference system (ANFIS) to estimate critical flashover voltage on polluted insulators. Diameter, height, creepage distance, form factor and equivalent salt deposit density were used as input variables for ANFIS, and critical flashover voltage was estimated. In order to train the network and to test its performance, the data sets are derived from experimental results obtained from the literature and a mathematical model. Obtained results were given in both tabulated and graphical form for various cases studies, separately. Satisfactory and more accurate results obtained by using ANFIS to estimate the critical flashover voltage for the considered conditions compared with the previous works. Both test and validation stages were explained in detail and it is observed that estimated results rather close to experimental results.

Contamination level evaluation on Colombian north cost

This paper presents the contamination levels, obtained applying the Equivalent Salt Deposit Density ESDD methodology in nine distribution circuits and five substations, belonging to ELECTRICARIBE S.A. E.S.P., and located in the north area of Barranquilla, the main Colombian Atlantic Ocean port. The paper shows the different study stages such as the sampling places selection and configuration, the ESDD measurement procedures and the results evaluation applying statistical techniques.

A single-chip Zero-IF down-converter in SiGe:C BiCMOS technology for WLAN 802.11a

This paper presents the contamination levels, obtained applying the Equivalent Salt Deposit Density ESDD methodology in nine distribution circuits and five substations, belonging to ELECTRICARIBE S.A. E.S.P., and located in the north area of Barranquilla, the main Colombian Atlantic Ocean port. The paper shows the different study stages such as the sampling places selection and configuration, the ESDD measurement procedures and the results evaluation applying statistical techniques.

Study on AC pollution flashover performance of composite insulators at high altitude sites of 2800-4500 m

The newly constructed Qinghai-Tibet Railway connecting Golumd and Lhasa is the highest railway in the world, which is located on the hinterland of Qinghai- Tibet Plateau with the average altitude of above 4000 m. Therefore, the external insulation of electric equipments will be affected by the atmospheric conditions in the high altitude regions. In contrast to many test investigations in the artificial climate chamber, there are few ones at the high altitude sites of 3000 m and above. In the paper, the AC artificial pollution tests of four types of composite insulators are carried out at three high altitude sites of 2820 m, 3575 m and 4484 m along the Qinghai-Tibet Railway. The test results show that the AC pollution flashover voltages in high altitude regions are affected not only by the pollution grades but also by the atmospheric parameters. The pollution flashover voltages will decrease with the increase of air pressure but increase with the decreases of ambient temperature. The exponent characterizing the influence of equivalent salt deposit density is 0.26 to 0.32 and the exponent characterizing the influence of non-soluble deposit density is 0.12 to 0.16, the influence of non-soluble deposit density cannot be neglected. The exponent characterizing the influence of air pressure is 0.507 to 0.587. The exponent characterizing the influence of ambient temperature is about 0.20. Considering the combined influence of the air pressure and ambient temperature, the AC flashover voltage of the polluted composite insulators will decrease by 4.0% to 6.4% for the altitude increased per 1000 m.

Artificial neural network optimisation methodology for the estimation of the critical flashover voltage on insulators

To describe an artificial neural network (ANN) methodology in order to estimate the critical flashover voltage on polluted insulators is the objective here. The methodology uses as input variables characteristics of the insulator such as diameter, height, creepage distance, form factor and equivalent salt deposit density, and it estimates the critical flashover voltage based on an ANN. For each ANN training algorithm, an optimisation process is conducted regarding the values of crucial parameters such as the number of neurons and so on using the training set. The success of each algorithm in estimating the critical flashover voltage is measured by the correlation index between the experimental and estimated values for the evaluation set, and finally the ANN with the correlation index closest to 1 is specified. For this ANN and the respective algorithm, the critical flashover voltage of the test set insulators is estimated and the respective confidence intervals are calculated through the re-sampling method.

Calculation of leakage current density of silicone rubber insulators under accelerated aging conditions

The paper presents two different methods to calculate the current density along silicone rubber (SiR) insulator surface under salt-fog testing conditions. The first method which is based on field theory approach uses the commercial software COMSOL ® to compute the current density. The conductivity of the contamination layer used in the calculations was extracted from the measured equivalent salt deposit density (ESDD) separately for different regions of the insulator surfaces. The second method is based on circuit theory approach. The insulator surface was divided into different sections for resistance calculations to account for different contamination levels. Rankings based on the calculated current densities based on segmentation of the insulator surface for ESDD measurements match with those extracted from measured leakage currents.

Prediction of equivalent salt deposit density of contaminated glass plates using artificial neural networks

Contaminants are deposited on the outdoor insulator surface due to environmental conditions. Conductivity or Equivalent Salt Deposit Density (ESDD) normally expresses this contamination on the insulator surface. In the laboratory, NaCl, tap water and distilled water are used for measuring conductivity and ESDD. In addition, different sizes of glass plates are used as an insulating medium. A conductivity-measuring instrument (Cond 300i) is used to measure the conductivity of the salt-solution. Based on the experimental data, the relationship between the different variables (temperature, salinity, salt, type of water, plate size and sigma) and the ESDD are modeled using artificial neural networks. The developed model showed a good predictive success with R 2 value above 0.98. This value indicates high accuracy for both model development and the model generalization capability. The meteorological variables (temperature, salinity, salt, type of water, plate size, etc.) with the greatest influence on ESDD are also identified using the weight partitioning method. It is found that glass plate size is the variable that has the greatest effect on the prediction of the ESDD since it has a contribution of 47%. The volume conductivity at different degrees had a contribution between 12.38% and 12.87%, while the type of water, the salt quantity, the salinity, and the temperature used had a contribution percentage of 7.92, 7.92, 7.43, and 4.46, respectively. The investigation indicated that the ANN models are well-suited for predicting the contamination level to prevent flashover on the insulator surface and for analyzing the contribution of the different factors affecting this contamination level that are represented either by the ESDD or the conductivity. Additionally, the ANN models can be extended for other applications in which nonlinear relationships are observed.

Study on AC Artificial-Contaminated Flashover Performance of Various Types of Insulators

Artificial pollution tests have been carried out to study AC flashover performances of various types of porcelain, glass, and polymeric insulators in this paper. The experimental results show that the polluted flashover voltage Uf is affected by equivalent salt deposit density rhoESDD and nonsoluble deposit density rhoNSDD, the influences of which are independent of each other. Based on the analyses of the flashover voltages, the correction formulas of the flashover voltages Uf of various insulators at various rhoESDD and rhoNSDD levels are pointed out. The experimental results also show that there is a distinct difference among the flashover voltages of various types of polluted insulators. At the same pollution degree, the antipollution performance of the fog-type glass insulator is better than those of the outer-rib porcelain insulators. In terms of the effectiveness of creepage distance of insulators, the antipollution performance of polymeric insulators is superior to those of porcelain and glass insulators.

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

Design of an artificial neural network for the estimation of the flashover voltage on insulators

This work attempts to apply an artificial neural network in order to estimate the critical flashover voltage on polluted insulators. The artificial neural network uses as input variables the following characteristics of the insulator: diameter, height, creepage distance, form factor and equivalent salt deposit density, and estimates the critical flashover voltage. The data used to train the network and test its performance is derived from experimental measurements and a mathematical model. Various cases have been studied and their results presented separately. Training and testing sets have been modified for each case.

Determination of equivalent salt deposit density using wind velocity for a contaminated insulator

This paper illustrates a new analytical model for determining equivalent salt deposit density (ESDD) on contaminated insulators using wind velocity. The analytical model is derived using the dimensional analysis technique. The values of ESDD from the analytical model are calculated using different values of wind velocity. These results are compared with the experimental results obtained from sites. The analytical results are also compared with the polynomial model output obtained via least-squares analysis of experimental data. It is found that the results obtained by the analytical model are quite consistent with the experimental results for different range of wind velocity.

Correlation among ESDD, NSDD and leakage current in distribution insulators

The maintenance of distribution networks is more effective if the insulation contamination levels are known. The selection of measuring methods of pollution levels is then crucial. The relationship between several evaluation methods of pollution levels and the operating behaviour of several insulator profiles in a polluted zone is described. Laboratory tests were carried out to reproduce pollution levels found in the field. The quantity of non-soluble materials deposited over the insulators' surface affect the magnitude of the leakage current generated over a contaminated insulator. The relationship that defines leakage current with respect to the equivalent salt deposit density (ESDD) level for a specific non-soluble material level is almost linear, from which it is possible to develop a relationship between them for each insulator.

Influence of shed parameters on the aging performance of silicone rubber insulators in salt-fog

The paper presents the results of a study on the effect of shed design on the aging performance of silicone rubber (SIR) insulators in salt-fog. The experiments on a single shed design at 35 V/mm average stress and 0.25 S/m salt-fog conductivity level are reported. Shed diameter, location and inclination angle are the parameters investigated in the study. The low frequency harmonics of the leakage current, early aging period, equivalent salt deposit density (ESDD), and physical damage are used to evaluate the aging performance of various designs. Insulators having sheds with 100 mm diameter show a better performance than those having 80, 60 and 40 mm diameter sheds. The inclination angle of the sheds is shown to have a significant effect in reducing the leakage current to a very low value but simulation results using FEMLAB/sup /spl reg// show that a steep inclination angle results in field enhancement beneath the shed that may lead to corona damage of the shed. A cup shaped design for the shed is shown to have a low leakage current level and a low field enhancement beneath the shed.

Measurements of equivalent salt deposit density (ESDD) on a suspension insulator

Equivalent salt deposit density (ESDD) is widely used to describe the state of contaminated insulators. In this paper, a new method of ESDD on-site measurement is studied. Two types of sensors are designed, which can not only carry enough water for the contamination on the insulator surface to dissolve and cover the insulator surface with conducting solution, but also measure the conductance of the solution. The design of the sensors and the determination of the desired parameter are introduced in detail. Experiments prove that the conductance of the contamination solution is linear with the square root of ESDD of the insulator. This relationship can also be deduced by Debye-Huckel-Onsager theory. According to this relationship, the conductance measured by the sensor can be converted to ESDD. Therefore, Measuring ESDD on-site can be realized.

Surface Resistance Measurements on Nonceramic Insulators

The results and analysis of surface resistance measurements performed on nonceramic insulators (NCI) are presented in this paper. The goal of this study was to determine if the surface resistance measurement procedure can be formalized to ensure repeatable and reproducible results. The NCIs evaluated had housing materials made from one type of silicone rubber and one type of ethylene propylene diene terpolymers (EPDM) rubber. A porcelain post insulator was used as a reference. The Task Force concluded that it is possible to establish a standard for surface resistance measurement in the laboratory. Such a standard is valuable since surface resistance provides: (1) an indication of aging on NCI housing material, and (2) a more sensitive indicator of true contamination severity on insulators than provided by conventional equivalent salt deposit density (ESDD) measurements. As a first step in this direction, guidelines for measurement have been provided in this paper. Suggestions for future work needed for standardization are also included in the paper.

Surface resistance measurements on nonceramic insulators

The results and analysis of surface resistance measurements performed on nonceramic insulators (NCI) are presented in this paper. The goal of this study was to determine if the surface resistance measurement procedure can be formalized to ensure repeatable and reproducible results. The NCIs evaluated had housing materials made from one type of silicone rubber and one type of ethylene propylene diene terpolymers (EPDM) rubber. A porcelain post insulator was used as a reference. The Task Force concluded that it is possible to establish a standard for surface resistance measurement in the laboratory. Such a standard is valuable since surface resistance provides: (1) an indication of aging on NCI housing material, and (2) a more sensitive indicator of true contamination severity on insulators than provided by conventional ESDD (equivalent salt deposit density) measurements. As a first step in this direction, guidelines for measurement have been provided in this paper. Suggestions for future work needed for standardization are also included in the paper.

Derivation of creepage distance in terms of ESDD and diameter of the contaminated insulator

In designing EHV transmission systems, specific knowledge about the creepage distance of the insulator, which is subjected to adverse environmental contamination, is important. Various system components' configurations can be properly coordinated through the appropriate application of the relationship between insulator creepage distance, the equivalent salt deposit density (ESDD), and the insulator diameter. In this paper, a general relationship between the creepage distance, ESDD, and diameter of the insulator has been proposed using the dimensional analysis technique.

Relation between leakage impedance and equivalent salt deposit density on an insulator under a saltwater spray

The degree of pollution of an insulator polluted rapidly under a saltwater spray is observed by measurement of the leakage current, which flows between electrodes fixed on the surface of the insulator, under 30 V ac voltage. Long rod insulators were used as samples. The relation between the leakage impedance and the equivalent salt deposit density (ESDD) of the insulators was obtained under several experimental conditions. As a result, the following was found (1) the effect of the wind velocity on the insulator is small, and is especially small when the distance between the electrodes is short, (2) the effect of the distribution of the saltwater drops on the insulator is small, and (3) the leakage impedance does not depend on initial dryness of the insulator surface (and the conductance is low) before the saltwater spray. It is important that the ESDD be above a certain value, and that the distance between the electrodes be short. Furthermore, it was shown that ESDD can be estimated fairly exactly from the leakage impedance.