Post Insulators Research Articles

Online applicable techniques to evaluate field leakage current waveforms

Leakage current monitoring is widely employed in order to investigate electrical surface activity and overall performance of high voltage insulators. Both activity and performance are closely linked with local conditions and experienced pollution. Therefore, field measurements are necessary to acquire an exact view of experienced activity and performance. However, field noise and the size of accumulated data are issues of concern in the case of field monitoring. In this paper, 75,887 leakage current waveforms obtained through more than six years of monitoring on 18 post insulators of different material, installed at two different 150 kV substations exposed to marine and industrial pollution, are investigated in order to evaluate the noise and data size problems. Three different types of noise are identified and their impact on raw data as well as their contribution to the data size is evaluated. Three different techniques are proposed to cope with the noise and data size problems. The techniques are selected so as to be online and hardware applicable in order to be incorporated in improved leakage current monitoring systems. Each technique is evaluated individually and in combination with the others. Combined use of all three, is proposed as a prerecording stage, able of coping with both noise and data size problems.

Impact of noise related waveforms on long term field leakage current measurements

Leakage current (LC) monitoring is widely employed in order to investigate electrical surface activity on high voltage (HV) insulators. Long term field monitoring is required in order to obtain an actual view of the phenomena. Therefore any monitoring system is bound to encounter data size problems. A number of solutions have been proposed to address this problem by extracting different values from the measured waveforms as a performance indication. However, a parameter that is fully representative of the waveform is yet to be determined. Hence, measuring and storing of the actual LC waveform is still required on sites for research and monitoring purposes. In addition, field related noise can result to misinterpretation of the actual activity. In this paper, a number of 26089 waveforms, recorded in a 150 kV Substation on four different post insulators that are part of the grid, are investigated. The monitoring period exceeded six years. Different techniques are applied and evaluated on the data set, employing simple numeric criteria and more advanced techniques such as Fourier and Wavelet analysis. Results are presented towards addressing the problems of noise and data size. The study objective is the incorporation of the results in improved leakage current monitoring systems.

Automating the Classification of Field Leakage Current Waveforms

Leakage current monitoring is widely employed to investigate the performance of high voltage insulators and the development of surface activity. Field measurements offer an exact view of experienced activity and insulators’ performance, which are strongly correlated to local conditions. The required long term monitoring however, results to the accumulation of vast amounts of data. Therefore, an identification system for the classification of field leakage current waveforms rises as a necessity. In this paper, a number of 500 leakage current waveforms recorded on a composite post insulator installed at a 150 kV High Voltage Substation suffering from intense marine pollution, are investigated. The insulator was monitored for a period of 13 months. An identification system is designed based on the considered data employing Fourier analysis, wavelet multiresolution analysis and a neural network. Results show the large impact of noise in field measurements and the effectiveness of the discussed system on the considered data set.

Finite element analysis of electric field around an ice-covered semi-conducting glazed insulator using a form of Kelvin transformation

This paper describes electric field distributions around a semi-conducting glazed standard post insulator for power frequency, lightning impulse(1.2/50 μs) and switching impulse(250/2500 μs) voltages under icing conditions, which were computed numerically using finite element method. Thin glaze coating on the insulator requires a very large number of elements for finite element analysis because of an open boundary around an ice-covered insulator. To reduce number of elements and hence computation time, the region between domain of interest and infinity was modeled by a form of Kelvin transformation. Simulation results are compared with laboratory experiments and are found to be in agreement.

Development of a positive creeping discharge along an aerial insulated wire

AbstractIn high‐voltage aerial distribution systems, the insulated cables are supported by the binding wire with the post insulator at the utility pole. When a lightning strike occurs in the neighborhood of the insulated cable in an aerial power distribution system, inductive lightning surges invade the central line of the cable. Then, creeping discharges develop along the cable surface from the binding wire tip at the same time as flashover of the post insulator at a supporting point of the cable. If the cable insulator has weak points such as pinholes, a malfunction near the cable supporting point may occur, with melting of the wire due to punch‐through breakdown. To prevent such accidents, it is important to clarify the mechanism of the creeping discharge along the insulated cable caused by the lightning strike. The polarity of creeping discharges depends on the polarity of the inductive lightning surges, and the extension length and aspect of the discharge differ greatly depending on the discharge polarity. The development of these creeping discharges is attributed to complicated behavior of the positive and negative electric charges.In the present study, we examined in detail the development of a positive creeping discharge along a wire surface by using a high‐speed image converter camera. This paper describes the mechanism of development of a positive creeping discharge based on the experimental results. 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(3): 20–29, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20997

Restoration of the insulation of ice-covered post insulators

This article describes a technique used to deice and restore the external insulation of post insulators covered with ice in the process of melting. Tests were done in the large environmental chamber at Université du Québec à Chicoutimi's research pavillion on atmospheric icing. Post insulators were covered with ice and subjected to conditions close to the electrical flashover. The surface of the post insulators was cleaned with a powerful steam jet. This considerably reduced the leakage currents and, as a result, the insulation of the post insulators could be restored. The improvement of the insulation was estimated based on a simple model where the arc is propagated on a polluted surface.

Monitoring leakage current of ice-covered station post insulators using artificial neural networks

This paper presents the analysis of leakage current evolution of an ice-covered station post insulator during a melting period using artificial neural network (ANN) models. The tests, carried out under wet-grown ice regime for different experimental conditions, showed that the permanent establishment of white arcs, identified as ?permanent regime? led to flashover in the large majority of the cases,. Based on these observations, the development of a monitoring methodology aimed at forewarning the approach of the leading white arc during melting periods is proposed. The monitoring methodology uses different ANNs in order to predict the appearance of the white arc based on the identification, classification and analysis of the occurrence frequency of electric discharges. The results show that the ANN monitoring model developed is able to predict the onset of permanent regime under various experimental conditions. Hence, it was found that the delay between the permanent regime onset prediction delivered by the ANN model and its realization is 9 minutes on average. These results confirm that the proposed ANN model could be used as part of a monitoring system for post insulators during icing events for protection against potential flashover hazards.

Leakage Currents on Naturally Contaminated Porcelain and Silicone Insulators

The leakage current measurements on standard post insulators and on rod insulators without sheds were carried out. The porcelain and silicone rubber insulators were tested at the Glogow station under the voltage of 75 kV. It was shown that the currents on porcelain insulators are sometimes greater than the currents on silicone insulators. However, the currents on both insulator types are often similar. Silicone rubber insulators are more contaminated than porcelain insulators. The current analysis has been made by using the static theory of pollution flashover.

Acoustic investigations of long-rod insulators and their material properties

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

Development of a Novel Live-Line Inspection Robot System for Post Insulators at 220-kV Substations

Based on investigating existing on-line detection methods for energized ceramic post insulators, this paper proposes a new live-line work robot involving ultrasonic detection for flaws in porcelain post insulators at 220-kV high-voltage (HV) substations. Owing to the HV, strong electromagnetic field and space conditions, the robot would be a special one. Thus, on the basis of studying correlative technologies — mechanism design, visual alignment and location, HV insulation, electromagnetic compatibility, automatic control, and wireless communication — each part of the robot system is designed and analyzed. The experiment and trial operation results show that the designed robot can work normally in 220-kV substations, and cracks in porcelain post insulators can be detected effectively, safely and conveniently by the robot.

Development of Arc-Guided Protection Devices Against Lightning Breakage of Covered Conductors on Distribution Lines

The breakage of overhead covered conductors on distribution lines resulting from the short-circuit arcs caused by lightning flash becomes a challenge as the application of covered conductors increases on distribution lines. Based on various methodologies and devices developed to avoid the covered conductor breakage in the world, novel arc-guided devices, including arcing protection hardware with barbs, clamping post composite insulator, and barb electrode clamping post porcelain/composite insulator are presented in this paper. Experimental results are also presented to validate these new developed devices. Devices based on the developed technologies have been widely applied on the power grids in China successfully.

Leakage Current and Discharge Phenomenon of Outdoor Insulators

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.

Designing a New Post Insulator Using 3-D Electric-Field Analysis

Insulators are very important elements of electric power systems. This paper introduces an analysis of electrical conditions in the area between the conductor and the insulator's upperfitting. The designing of new a composite post insulator is presented with the upperfitting made of insulating material. Previous composite post insulators have had upperfittings made of conducting material metal. 3D analysis of electric-field strength in the insulator and its surroundings are also given. The computation was carried out by using the OPERA Vector Fields program tool. The results of this analysis are presented for both-new and old versions of a composite post insulator. 3D analysis shows that the new version has up to five times lower magnitudes of electric-field strength.

Evaluating station post insulator performance from electric field calculations

This paper illustrates the use of electric field calculations for evaluating the performance of porcelain post insulators in stations for AC system voltages up to 1200 kV. The electric field was calculated using a 3-dimensional commercially available computer package that is based on the Boundary Element Analysis method. A comparison has been made of the effectiveness of several commonly used methods for improving contamination performance, namely, adding leakage distance (taller posts, ribbed sheds and creepage extenders) and coating the insulator with hydrophobic materials. It is shown that for station post insulators used in EHV and UHV systems (greater than 240 kV), coating the insulators with hydrophobic materials or replacing them with composite insulators offers superior protection to flashovers initiated under wet and contaminated conditions than provided by methods that simply increase the leakage distance. For lower voltages (less than 240 kV), all methods considered are effective.

An ultrasonic on-line test method for detecting remotely and automatically energised porcelain post insulators in high-voltage substations

The fracture of ceramic post insulators in substations is a very important factor which disturbs the normal working of high-voltage (HV) substations. Every year there are some serious grid accidents caused by the fracture of ceramic post insulators in some countries. The fracture is usually caused by the propagation of the crack. Therefore, in this paper, an ultrasonic on-line test method for inspecting automatically the internal crack of the energised porcelain post insulator at 220 kV substations is introduced to prevent the fracture. The correlative ultrasonic detection technology of the energised ceramic post insulators is investigated. Furthermore, an inspection mechanism and robotised inspection system with good insulation safety property and electromagnetic compatibility (EMC) performance are designed. The experimental results show that, even in the high-voltage and strong magnetic field circumstance in substations, the live-line remote inspection of energised porcelain post insulators can be accomplished safely, conveniently, steadily, reliably and effectively with this method.

Effect of core diameter of cylindrical polymer insulators on contamination flashover voltage—part I

AbstractThis paper presents the investigation results of the effect of the core diameter on the flashover voltage of cylindrical polymer insulators under contaminated and heavy fog conditions. The specimens had the same or very similar shed profiles but different core diameters. The results confirmed a large reduction in flashover voltage when the core diameter was increased from 26 mm for transmission line insulators to 73 mm for post insulators; however, change is not so significant from post insulators to bushing shells having larger core diameters. Higher flashover voltages of line insulators are attributable to the large difference in the leakage current density between the trunk and shed portions so that the wetting conditions are very different between these portions. This causes the applied voltage to the whole insulator to be divided and allotted to almost all the dried trunks, preventing the concentration of the applied voltage to only a few portions, resulting in higher flashover voltages. The quantitative assessment of contamination flashover voltage characteristics of hydrophobic polymer insulators presented in this paper will be helpful in the selection and design of polymer insulators for contamination areas. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Adaptation of the 1 MV bushing to the SINGAP concept for the ITER NB injector test bed

The 1 MV bushing of the ITER NB injector is probably one of the most challenging components of the whole accelerator, since such a high voltage (HV) in a contaminated and radiated environment requires the development of non-standard technologies. This paper intends to provide a guideline for the design of 1 MV bushing for the ITER neutral beam injector test bed. Although mainly focused on the SINGAP alternative concept of the injector, the reported general criteria can be useful for the design of other HV components, such as post insulators of the acceleration grids. For every different kind of required insulation, basic physical models describing breakdown phenomena are reported together with the main technological implications and the practical recommendations necessary to improve insulation performance. The results of the finite element analyses of 1 MV bushing, operating at CEA—Cadarache laboratories, are used to validate general criteria in a typical geometry. The effects of radiation, such as neutrons and gamma rays, on solid insulators and gases have also been taken into account, describing the most important phenomena and the related implications in terms of voltage hold-off capabilities. Finally the design of the bushing in the SINGAP option and the solutions adopted are described.

Use of an optimization algorithm in designing medium-voltage switchgear insulation elements

Modern design of medium-voltage switchgear insulation elements is based upon the use of optimization methods. This paper presents an algorithm for the design of such elements using numerical calculations on the basis of the finite elements method in connection with evolution optimization methods. The use of differential evolution and evolution strategy algorithms is presented in the case of modeling a medium-voltage post insulator, the secondary function of which is voltage indication. A comparison between these two algorithms is also presented. The task of both optimization algorithms is to find an adequate capacitance of the voltage divider and the optimal distribution of electric field strength. All other requirements and constraints that have to be taken into consideration in the design of insulation elements are also included in the algorithm

Insulating safety analysis of the hot-line sweeping robot

This paper presents a method of calculating the insulating safety distances for hot-line working robots at high voltage when dielectric is adulterated with conducts. Also, finite element method is adopted to calculate the electric field strength to find whether it is beyond the critical. The above methods have been applied to analyze the insulating safety of the robot for hot-line sweeping post insulators in a 220 KV substation. They have also been testified by experimentations.

Potential and electric-field distributions around an ice-covered post-type insulator

To facilitate the study of phenomena preceding the flashover of an ice-covered station post insulator during a melting period, the potential and electric-field distributions along the insulator have been numerically calculated. Commercial software based on the boundary element method was used for this purpose, and a simplified three-dimensional model of the ice-covered insulator was developed and validated experimentally. Then, a station post insulator covered with wet-grown ice under a melting regime was numerically simulated on the basis of experimental results. The presence of a conducting water film at the ice surface, the shedding of ice deposits, and the presence of a partial electric arc along an air gap were taken into account in the simulations. The results obtained have made it possible to show that the water film, the number of intervals of air, and the presence of partial arcs have a considerable effect on the distribution of the potential and the electric field along the insulator. In the same way, the appearance of a partial arc as well as the occurrence of ice shedding lead to a redistribution of the potential along the ice deposit, either supporting or inhibiting the flashover process. The results obtained will help to improve insulator geometry for cold climate regions.