The ultra-high frequency (UHF) method has been widely used in a gas-insulated system (GIS) for partial-discharge detection, and many achievements have been realised. In addition, many studies based ...on artificial defects have been made to confirm its validity. Therefore, the UHF method is generally believed to be sufficiently effective for GIS monitoring. However, in practical application, the authors find that for some micro-crack discharge in GIS insulator, the UHF method has low sensitivity. To fully study the characteristics of the micro-crack discharge in the GIS insulator, an experiment is conducted in this study using an actual post insulator with a micro-crack defect. The current signal based on IEC 60270 standard and the radio-frequency electromagnetic signal is simultaneously measured for thorough analysis. The results show that some submillimetre crack defects may occur in the GIS insulator. Its discharge is mainly presented as glow discharge, and the discharge signal frequency usually cannot reach the UHF band; thus, it cannot be effectively detected by the UHF method. This study provides complementary information to the applicability of the UHF method and inspires further study of the GIS insulator and its monitoring technology.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In order to study the effect of glaze erosion on the performance of porcelain post insulator, an inclined plane (IP) test similar to IEC 60587 standard was conducted on a cylindrical insulator sample ...under laboratory conditions for ac voltage, and a new test method, called graphite-layer-based glaze erosion test was proposed in this paper and performed on the sheds of a 40.5 kV post insulator. The experimental details of the graphite-layer-based glaze erosion test was introduced, the technical points of which are coating a graphite layer on the surface of the shed using a brush mold which contains multiple hollowed-out rhombic grids, and arranging high voltage electrode at shed root and grounded electrode at shed edge respectively at both ends of the graphite layer, so as to form continuous and stable surface arcing under ac voltage and therefore achieve desired glaze electrical erosion effect. The graphite layer is a uniform viscous mixture made up with flake graphite and liquid glue according to a quality ratio of 1:1.2. The arcing process, arc current characteristics, surface temperature, and glaze erosion appearance were analyzed. Leakage current under power frequency voltage and flashover voltage of the eroded cylindrical insulator by IP test were measured, while porosity test and scanning electron microscopy (SEM) tests were conducted on samples taken from the sheds after graphite-layer-based glaze erosion test. The results indicate that glaze erosion will decrease both electrical and mechanical performance of the porcelain post insulator. The new test method proposed in this paper has been proved to be effective for glaze erosion test and consumes much less time compared with IP test, which provides a new idea for accelerated tracking and erosion test of glaze and porcelain materials so as to study the aging characteristics of porcelain insulators.
Algae are found grow on the surface of room temperature vulcanized (RTV) silicone rubber coated insulators installed in warm and humid region such as Sichuan, which brings potential operating risk to ...power transmission and transformation equipment. In this research, two different types of 110kV RTV coated post insulators with algae growth were obtained from Sichuan. Firstly, the algae coverage rate of upper and lower surfaces of top, middle and bottom shed of insulators were calculated through the image processing method respectively. Then, the wet impulse puncture voltage and fog flashover voltage were tested on the algae-grow insulators as well as clean ones. Lastly, the equivalent salt deposit density (ESDD) and no soluble deposit density (NSDD) of insulators were measured. The results show that the algae on the lower surface of insulators are significantly less than the upper surface. Algae have no effect on impulse puncture voltage of insulators. However, the algae decrease the flashover voltage of insulators under the condition of steam fog by 25.2%∼44.0% compared to the clean ones.
This book is a collection of recent publications from researchers all over the globe in the broad area of high-voltage engineering. The presented research papers cover both experimental and ...simulation studies, with a focus on topics related to insulation monitoring using state-of-the-art sensors and advanced machine learning algorithms. Special attention was given in the Special Issue to partial discharge monitoring as one of the most important techniques in insulation condition assessment. Moreover, this Special Issue contains several articles which focus on different modeling techniques that help researchers to better evaluate the condition of insulation systems. Different power system assets are addressed in this book, including transformers, outdoor insulators, underground cables, and gas-insulated substations.
Thermal stress caused by different expansion coefficients of porcelain, cement and cast iron is one of the reasons that lead to fracture accidents of high voltage porcelain post insulators. In order ...to study the thermal stress distribution of post insulator, finite element model is established for numerical simulation calculation under different environmental temperatures contains steady state analysis and transient analysis. The results indicate that temperature variation cause stress concentration at the flange interface of post insulator, while the adverse effect caused by low temperature environment below zero degree centigrade is severer than high temperature.
To study the mechanical properties of porcelain post insulators, the finite element model was established by ANSYS to calculate stress and strain distribution under bending or torsion moments. ...Mechanical tests based on resistance strain measurement technology were carried out on the actual porcelain post insulators to measure their strain distribution. The results show that sheds will cause strain concentration at the roots of porcelain column whether the post insulator is bearing bending or torsion load. The stress and strain of shed roots gradually increase from top to bottom along the post insulator when bearing bending moment, while they are relatively uniform under torsion moment. It should be taken full account of the stress concentration caused by sheds during the selection or maintenance of porcelain post insulators.
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.
The main objective of this paper is to study numerically the influence of addition of 6 booster sheds (BS) to 2 units of EHV porcelain post insulator on their electrical performance under severe ...wet-grown ice accumulation based on experimental results. The numerical investigations have been carried out during melting period in order to determine the potential and electric field distributions and the voltage drop along the different air gaps resulting from the addition of BS. Numerical simulations were done using the finite element method (FEM). Adding BS helps to created artificially air gaps which length depends on their position along the ice-covered insulator. Numerical simulations have helped to demonstrate that voltage drop repartition along the different air gap is not uniform. In particularly, it was shown that more that 53% of the applied voltage is concentrated along the first air gap closed to the HV electrode, which also the longest. Also, it was demonstrated that numerical simulations can be useful and an interesting alternative to experimental test in order to improve and optimize the use of BS for improving electrical performance of post insulator under severe icing conditions.
Abstract-The moist air inside the HV switchgear can cause partial discharge (PD) on the surface of the post insulator, damaging the insulation performance. This paper explores the impact of humidity ...on the PD of post-insulators, analyzing the PD spectra and related parameters under varying humidity. The results show that when relative humidity is 40 %, the average discharge increases with voltage, yet the PD spectra remain similar under different voltages. When relative humidity reaches 60 % or 80 %, the spectra display diverse PD sources related to the distribution and movement of drops on the post insulator's surface at different voltages.
The main purpose of this work was to investigate the development trends of high voltage porcelain post insulators over the last decades. It also shows an analysis of the performance of a contemporary ...design of a shorter nonstandard layout and its agreement with the IEC standards. Despite of high demanding requirements on Ceramic Solid Core Post Insulators, the economical aspect becomes more and more important. Therefore the objective of insulator design is to develop a technically and economically optimized HV component, with a high grade of reliability over decades. If some parameters can be optimized like, arcing distance and length of the insulator, maximizing the mechanical strength and stiffness, minimizing the core diameter, maximizing the form factor and finding an optimal shed profile, material can be saved and therefore weight can be reduced also and costs. Due to a more sophisticated manufacturing process of high voltage insulator, they can be produced in a bigger length in one piece and thinner sheds than 40 years ago. The result of these measures are a longer arcing and creepage distance, less weight and most of all less electrically conducting parts. 40 years ago, the column design for an 800kV AC post insulator was a stack of 6 insulators, compared to two insulators nowadays. This work reflects the different developments of design between the past and in these days, because the question was raised: do post insulators need to have the same total height than 40 years ago despite of an improvement of manufacturing them.
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