Porcelain Post Insulator Research Articles

Flashover characteristics of contaminated post insulators covered with snow

The conductivity of contaminated insulator surface increases during snow melting, which is easy to lead to pollution flashover. In this paper, the effects of equal salt deposit density (ESDD) and snow height on the surface flashover voltage of porcelain post insulators are studied, and the snow flashover process is simulated by glass plate. The test results show that the flashover voltage of snow-covered insulator decreases with the increase of ESDD. The relationship between the flashover voltage and the ESDD is a negative power exponential function. When the conductivity of cooling water used for snow making is very low, the thicker the snow on the insulator, the higher the minimum flashover voltage during snow melting. The reason may be that the uneven snow melting leads to the longer flashover path and the large loss of NaCl in the pollution layer with the melting of snow. The simulated snow covering test using the glass plate shows that the arc develops along the glass surface inside the snow layer, and the arc path almost coincides with the melting area of the snow layer.

Finite element modeling and assessment of seismic response of electrical substations porcelain post insulators

The study presented in this paper focused on developing accurate computational finite element (FE) model of electrical substations ceramic (porcelain) post insulators. The objective is to investigate the structural behavior and seismic response of these critical equipment through detailed numerical simulations that can replace or minimize experimental qualification tests and optimize future design of electrical equipment. Detailed three-dimensional solid FE modeling was used to capture the complex geometry of post insulators and the brittle nature of ceramics. Dedicated material characterization tests were utilized to define the porcelain nonlinear material model parameters. The developed model was verified using previously conducted experiments and used to perform linear and nonlinear static and dynamic analyses. A sensitivity parametric study was conducted first to calibrate the model and rank the sources of uncertainties in porcelain insulator modeling using the so-called tornado diagram analysis. The calibrated model was further utilized to carry out nonlinear time history analysis under earthquake excitation and capture the dynamic mode of failure, which is not always feasible to achieve using experimental tests. The study concluded with identification of which modeling parameters significantly affect the simulated structural behavior of post insulators, and compared the inelastic response at failure under static and dynamic loading.

Analysis of the Research and Development Status and Future Development of Porcelain Insulator Fault Detection Equipment Based on a Portable Insulator Detection Device

Fault detection of porcelain post insulators has always been the research direction of power industry. At present, the insulator testing equipment still has some defects, such as high cost, complex operation and poor effect. For the design and development of fault detection equipment for porcelain insulators, this paper will introduce the design principle and basic structure of an insulator detection equipment based on a portable insulator fault detection equipment. In this paper, combined with modern science and technology, artificial intelligence and UAV technology are combined with insulator detection work to make innovation and prospect for the future development of insulator detection equipment.

Application of Acoustic Spectrum Analysis in Detection of Porcelain Post Insulators Based on a portable insulator detection equipment

Fault detection of porcelain post insulators has always been the research direction of power industry. At present, the related equipment for flaw detection of porcelain insulators still has some defects, such as high equipment cost, complex operation and poor detection effect. For the fault detection of porcelain post insulators, this paper will put forward a complete set of fault detection methods based on the application of acoustic spectrum analysis in the fault detection of porcelain post insulators. The equipment used is a portable insulator testing equipment independently designed by the research team based on the basic principle. Based on this method, a large number of comparative experiments and testing applications have been carried out, which verifies the effectiveness and reliability of the vibroacoustic testing method in the detection of porcelain post insulators.

Improvement of the polyurethane spring isolation device for HV post insulators and its evaluation by fragility curves

A novel seismic base isolation system has been developed for high-voltage (HV) porcelain post insulators. The seismic isolation device consists of two steel plates, four polyurethane springs, and a steel rod, which are low-cost components compared to the post insulators. Two alternative designs of the device are experimentally and numerically assessed in this article. A simple and robust numerical model consisting of linear line elements and nonlinear springs was generated, and subsequently validated using the experimental results. Incremental dynamic analyses (IDAs) were then performed to obtain fragility curves. Ten historical earthquake profiles, scaled to intensities between 0.1 and 2.0 g, were then applied to the numerical models. The fragility curves, generated according to the latest version of IEEE-693, demonstrate that the seismic isolation devices are highly effective in diminishing the base moment of the porcelain insulator. It should be noted that relatively large displacements at the top of the pole must be accounted for by ensuring adequate slackness in the flexible conductors.

Infrared Detection and Thermoelectric Coupling Simulation Analysis of 220 kV Insulator Abnormal Heating

Heat and pollution flash caused by surface contamination are one of the common defects of insulators. If not discovered and eliminated in time, it will cause the deterioration of the insulator and seriously affect the service life of the insulator. If we can grasp the temperature distribution characteristics of the insulator in the state of contamination, the infrared temperature measurement can be used to quickly find and eliminate defects in a timely manner. This paper introduces a large area heating defect of porcelain post insulator and composite suspension insulator in 220kV equipment area, whose temperature distribution showed the rule of overheating at the high-voltage end and the temperature gradually decreasing toward the low-pressure end. Based on the field infrared temperature measurement and thermal image characteristics, it preliminarily analyzed that the heating was caused by insulator contamination and damp. Then, combined with pollution sampling, three-dimensional model establishment and thermoelectric coupling simulation calculation, the correctness of the above conclusions was verified, and preventive measures and suggestions were put forward.

Improving reliability of porcelain post insulators at electric power Substations

At electric power substations, post insulators are designed for isolation and fastening of conductive parts of electrical installations. Insulators are installed on outdoor switchgear of substations as part of the main switching equipment. During operation, they are exposed to external atmospheric effects, mechanical and dynamic loads. Timely replacement of post insulators increases significantly the reliability of the main substation equipment at power substations. The question of improving reliability at transformer and traction substations is considered, external and internal factors associated with destruction of porcelain post insulators (PPI) are presented. It is established that the main cause of damage to PPI are sharp changes in ambient temperature, especially the transition of temperature values through 0°C. A model of a porcelain post insulator with an insulating body of elliptic shape is proposed. Operation of the proposed device is described. Analysis is presented of the ratio of the lengths of the axes of a circle and ellipse (major-to-minor) as related to spatial positioning in power loads. It has been determined by calculation that a post insulator should be installed in such a way that the major axis of the ellipse be aligned in the direction of the temperature gradient — sunlight, to reduce the impact of heating on the minor axis of the insulator.

Detecting Defects in Porcelain Postinsulator Coated With Room Temperature Vulcanized Silicone Rubber by Pulsed Thermography

Nondestructive testing is of great significance for preventing fracture accidents of porcelain postinsulators, especially coated with room temperature vulcanized (RTV) silicone rubber. In this paper, the feasibility of pulsed thermography for defects detection of porcelain postinsulators was investigated. 110-kV porcelain postinsulators with crack defects were tested by utilizing the investigated approach. The results show that crack defect as small as 0.4 mm under the RTV silicone rubber coating with the thickness of 1 mm can be accurately identified. Homomorphic filtering method with Fourier transform was applied to correct the nonuniform heating and improve the defect contrast in the thermal images. With the advantages of simple operation, contactless measurement, full-field imaging, and quantitative defect estimation capability, the pulsed thermography would have promising applications in live detection of porcelain postinsulators.

Ceramic and hybrid support insulators for UHVDC systems

The requirements for UHVDC installations in terms of length, mechanical strength, permissible deflection, creepage distance, shed profiles and pollution resistance are still a challenge for all existing technologies and solutions. Based on the positive long time experience with solid core porcelain post insulators and the pollution experience of insulators with silicone housings the fundamental concept of both were used to develop a new type post insulator with inside ceramic core and housing of silicone. The challenge was to provide a reliable and economical solution, which combines the advantages of both technologies. Realising the needs for high strength, low deflection under load for many applications PPC Insulators Austria began the development of hybrid post insulators. The ceramic solid core design provides superior advantages in terms of bending strength, also for torsion load and compression load. The silicone rubber housing allows thinner sheds and greater creepage distances, provides improved long term pollution flashover performance and protects the core from short circuit arc damage. As design for DC hybrid post insulators was chosen upright tapered, uniform and underhung tapered insulators columns stacked of single hybrid insulator sections. The single sections could be varied in core diameter, length, creepage distance, fittings and holepattern. The shed profile used for DC applications was defined according the recommendations given by CIGRE. Selected design tests, electrical and mechanical type tests were conducted according to the relevant parts of IEC standards for composite and ceramic insulators. Also a long term test installation was performed to establish a confidence in this product. The long term test installation has been energized at 725 kV DC and later the voltage was increased to 761 kV DC. The tests have served well in providing final qualification. Beside these voltage tests measurements of ESDD/NSDD, hydrophobicity and also visual inspections were carried out. The mechanical properties were driven from the seismic requirements and have been calculated by finite element modelling of the reactor and its support structure. For post insulators with silicone rubber sheds and with solid core porcelain may be the most stable solution and this type has been adopted in different 800 kV projects. One of the new insulator was chosen for smoothing reactor support for 800 kV DC system in India.

Investigation of DC discharge behavior of polluted porcelain post insulator in artificial rain

The surface discharge of natural polluted post insulators in rain is an important factor which affects the external insulation of HVDC converter stations. With the artificial contamination flashover tests in rain for porcelain post insulators, this paper has obtained the flashover process and discharge characteristics of the test samples under artificial rain condition. It has been observed that the discharge of water droplet on the shed edge plays a very important role in the whole process of pollution flashover in rain. When a water droplet hangs on the shed edge, the maximum electric field strength appears in the vicinity of vertices, rather than the lateral area of the water droplet. Thus, the streamer propagates only in the direction of the air gap between sheds. Moreover, the influence of raining conditions including intensity and conductivity on the flashover voltage has been investigated. Test phenomena also indicate that due to the different damp and dry band conditions, surface discharge characteristics of post insulator in rain are different with that in fog, which lead to different flashover voltages. This study provides a new understanding for the HVDC insulator pollution flashover in wet environment.

Study on glaze electrical erosion characteristics of porcelain post insulator by using inclined plane and graphite-layer-based method

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-layerbased 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.

Study on Bending and Twisting Mechanical Properties of High Voltage Porcelain Post Insulator

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.

Thermal Stress Analysis of High Voltage Porcelain Post Insulator

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.

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.

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.

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.

The AC-behavior of a hydrophilic and hydrophobic post insulator during rain

The AC-behavior of a hydrophilic and a hydrophobic porcelain post insulator is studied during four different rain conditions by measuring the electric field distribution, resistive and capacitive leakage currents and UV-photography of the discharge activity. The results are in agreement with each other and show resistive field distributions along the hydrophilic insulator at the normal operating voltage level. Electric field measurements reveal the deterioration in time of the surface hydrophobicity. Leakage current measurements are difficult to relate to electric field distributions, while electric field measurements and UV-photography are powerful tools to determine the condition of the insulator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Water-cooled generator connections

The increase in rating of generating plant in the past two decades has greatly increased the problems of conducting the power away to the distribution system. The conventional arrangement of naturally aircooled busbars has reached such a size that accommodation within the machine foundations is becoming increasingly difficult, and the use of forced cooling is an obvious solution. Forced-air cooling has been used, but the experience obtained with water cooling of stator windings has led to the application of this method to the generator connections. Two systems of generator connections using internal water cooling of the conductor have been developed, and are described in the paper. The first proceeded in two stages: the double-angle conductor of a nonsegregated busbar was replaced by a water-cooled tube supported on porcelain-post type insulators, and a water-cooled phase-isolated system using epoxy-resin insulators was developed. The second system involved the use of water-cooled cables. Design aspects of the two systems are discussed, prototype tests detailed and various installations described. This application of water cooling has been satisfactory, and various problems encountered during the development have been overcome. The experience gained indicates that designs can be produced for very much larger current ratings than those of the present installations without substantial increase in space requirements, and satisfactory connections of this type can be provided for the largest generators being designed or envisaged.