scholarly journals Is the Dry-Band Characteristic a Function of Pollution and Insulator Design?

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3607 ◽  
Author(s):  
Maurizio Albano ◽  
A. Manu Haddad ◽  
Nathan Bungay
Keyword(s):  
Vertical Axis ◽  
Design Guidelines ◽  
Textured Surface ◽  
Band Formation ◽  
Surface Design ◽  
Pollution Levels ◽  
Voltage Ramp ◽  
Band Characteristic ◽  
Geometrical Dimensions ◽  
Dry Bands

This paper assesses the dry-band formation and location during artificial pollution tests performed on a 4-shed 11kV insulator with conventional and textured surface designs in a clean-fog chamber and with the application of a voltage ramp-shape source. The different designs present the same overall geometrical dimensions, but the textured ones are characterized by the application of a patented insulator surface design. Three pollution levels, extremely high, high and moderate, were considered. A newly developed MATLAB procedure is able to automatically recognize the perimeter of the insulator, the trunk and shed areas on infra-red recordings. In addition, using the vertical axis identification, all trunks are subdivided into zones and into left and right areas, significantly increasing the capability of abnormalities detection. Any temperature increase within these areas enables to detect the appearance and the extension of dry bands. The results of the analysis of the statistical location and extension development over time of the dry bands during these set of comparative tests show a clear distinction between designs and pollution levels. These results may offer interesting design guidelines for dry-band control.

scholarly journals Image Analysis Determination of the Influence of Surface Structure of Silicone Rubbers on Biofouling

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Sevil Atarijabarzadeh ◽  
Fritjof Nilsson ◽  
Henrik Hillborg ◽  
Sigbritt Karlsson ◽  
Emma Strömberg
Keyword(s):  
Image Analysis ◽  
Silicone Rubber ◽  
Microbial Growth ◽  
Plane Surface ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Homogeneous Distribution ◽  
Textured Surface ◽  
Textured Surfaces ◽  
Band Formation

This study focuses on how the texture of the silicone rubber material affects the distribution of microbial growth on the surface of materials used for high voltage insulation. The analysis of surface wetting properties showed that the textured surfaces provide higher receding contact angles and therefore lower contact angle hysteresis. The textured surfaces decrease the risk for dry band formation and thus preserve the electrical properties of the material due to a more homogeneous distribution of water on the surface, which, however, promotes the formation of more extensive biofilms. The samples were inoculated with fungal suspension and incubated in a microenvironment chamber simulating authentic conditions in the field. The extent and distribution of microbial growth on the textured and plane surface samples representing the different parts of the insulator housing that is shank and shed were determined by visual inspection and image analysis methods. The results showed that the microbial growth was evenly distributed on the surface of the textured samples but restricted to limited areas on the plane samples. More intensive microbial growth was determined on the textured samples representing sheds. It would therefore be preferable to use the textured surface silicone rubber for the shank of the insulator.

Effects of Airfoil’s Polar Data in the Stall Region on the Estimation of Darrieus Wind Turbine Performance

2016 ◽  
Author(s):  
David Marten ◽  
Alessandro Bianchini ◽  
Georgios Pechlivanoglou ◽  
Francesco Balduzzi ◽  
Christian Navid Nayeri ◽  
...  
Keyword(s):  
Unsteady Aerodynamics ◽  
Vertical Axis ◽  
Design Guidelines ◽  
Operating Conditions ◽  
Performance Estimation ◽  
Simulation Methods ◽  
Computationally Efficient ◽  
Urban Context ◽  
Lift And Drag ◽  
Thrust And Torque

Interest in vertical-axis wind turbines (VAWTs) is experiencing a renaissance after most major research projects came to a standstill in the mid 90’s, in favour of conventional horizontal-axis turbines (HAWTs). Nowadays, the inherent advantages of the VAWT concept, especially in the Darrieus configuration, may outweigh their disadvantages in specific applications, like the urban context or floating platforms. To enable these concepts further, efficient, accurate, and robust aerodynamic prediction tools and design guidelines are needed for VAWTs, for which low-order simulation methods have not reached yet a maturity comparable to that of the Blade Element Momentum Theory for HAWTs’ applications. The two computationally efficient methods that are presently capable of capturing the unsteady aerodynamics of Darrieus turbines are the Double Multiple Streamtubes (DMS) Theory, based on momentum balances, and the Lifting Line Theory (LLT) coupled to a free vortex wake model. Both methods make use of tabulated lift and drag coefficients to compute the blade forces. Since the incidence angles range experienced by a VAWT blade is much wider than that of a HAWT blade, the accuracy of polars in describing the stall region and the transition towards the “thin plate like” behaviour has a large effect on simulation results. This paper will demonstrate the importance of stall and post-stall data handling in the performance estimation of Darrieus VAWTs. Using validated CFD simulations as a baseline, comparisons are provided for a blade in VAWT-like motion based on a DMS and a LLT code employing three sets of post-stall data obtained from a wind tunnel campaign, XFoil predictions extrapolated with the Viterna-Corrigan model and a combination of them. The polar extrapolation influence on quasi-steady operating conditions is shown and azimuthal variations of thrust and torque are compared for exemplary tip-speed ratios (TSRs). In addition, the major relevance of a proper dynamic stall model into both simulation methods is highlighted and discussed.

scholarly journals Modeling of Dry Band Formation and Arcing Processes on the Polluted Composite Insulator Surface

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3905
Author(s):  
Jiahong He ◽  
Kang He ◽  
Bingtuan Gao
Keyword(s):  
Energy Balance Equation ◽  
Field Calculation ◽  
Composite Insulator ◽  
Band Formation ◽  
Insulator Surface ◽  
Thermal Fields ◽  
Flashover Voltage ◽  
Before And After ◽  
Difference Time ◽  
Dry Bands

This paper modeled the dry band formation and arcing processes on the composite insulator surface to investigate the mechanism of dry band arcing and optimize the insulator geometry. The model calculates the instantaneous electric and thermal fields before and after arc initialization by a generalized finite difference time domain (GFDTD) method. This method improves the field calculation accuracy at a high precision requirement area and reduces the computational complexity at a low precision requirement area. Heat transfer on the insulator surface is evaluated by a thermal energy balance equation to simulate a dry band formation process. Flashover experiments were conducted under contaminated conditions to verify the theoretical model. Both simulation and experiments results show that dry bands were initially formed close to high voltage (HV) and ground electrodes because the electric field and leakage current density around electrode are higher when compared to other locations along the insulator creepage distance. Three geometry factors (creepage factor, shed angle, and alternative shed ratio) were optimized when the insulator creepage distances remained the same. Fifty percent flashover voltage and average duration time from dry band generation moment to flashover were calculated to evaluate the insulator performance under contaminated conditions. This model analyzes the dry band arcing process on the insulator surface and provides detailed information for engineers in composite insulator design.

scholarly journals Some design guidelines to adapt a Darrieus vertical axis turbine for use in hydrokinetic applications

2021 ◽  
Vol 312 ◽  
pp. 08017
Author(s):  
Francesco Balduzzi ◽  
Pier Francesco Melani ◽  
Giuseppe Soraperra ◽  
Alessandra Brighenti ◽  
Lorenzo Battisti ◽  
...  
Keyword(s):  
Fluid Dynamic ◽  
Vertical Axis ◽  
High Water ◽  
Design Guidelines ◽  
Rotor Blades ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Geometrical Parameters ◽  
Technical Literature ◽  
Downstream Flow

The use of vertical-axis turbines is raising interest in the field of hydropower production from rivers or water channels, where suitable mass flows are available, without the need of high water jumps or large construction sites. Although many optimization studies on vertical-axis turbines have been carried out for wind applications, lesser examples exist in the technical literature regarding hydrokinetic turbines. In the latter case, the best trade-off between power output and low structural stress is more dependent on the fluid dynamic loadings rather than the inertial loadings, due to the higher fluid density and lower rotation speed. The present work shows the results of an industrial study case application, in which the design of a traditional three-blade Darrieus rotor has been adapted for operating in water flows via hydrokinetic technology. Some specific design rules will be discussed, showing the different concepts adopted for the machine layout in order to achieve the best efficiency and performance. Multiple geometrical parameters of the rotor configuration were involved during the analysis: the number of rotor blades, i.e. two or three blades, the rotor’s shape, i.e. traditional H-shape or unconventional L-shape, and the use of power augmentation systems. The analysis of the numerical results was focused on the following output targets: maximum power coefficient, optimal tip speed ratio (TSR), rotor thrust, blade normal force and the upstream and downstream flow field influence. The outcome of the study shows how the best configuration differs from the common solutions for wind application. Moreover, a high power enhancement can be achieved while guaranteeing a good compromise in terms of structural loads.

Types of Size Disparity and the Perception of Surface Slant

Perception ◽  
1997 ◽  
Vol 26 (12) ◽  
pp. 1503-1517 ◽  
Author(s):  
Byron J Pierce ◽  
Ian P Howard
Keyword(s):  
Vertical Axis ◽  
Textured Surface ◽  
Curved Boundary ◽  
Surface Slant ◽  
Size Disparity ◽  
Horizontal Size ◽  
Depth Contrast ◽  
Depth Enhancement ◽  
Vertical Size

We examined (i) perceived slant of a textured surface about a vertical axis as a function of disparity magnitude for horizontal-size disparity, vertical-size disparity, and overall-size disparity; and (ii) interactions between patterns with various types and magnitudes of size disparity and superimposed or adjacent zero-disparity stimuli. Horizontal-size disparity produced slant which increased with increasing disparity, was enhanced by superimposed zero-disparity stimuli, and induced contrasting slant in superimposed or adjacent zero-disparity stimuli. Vertical-size disparity produced opposite slant (induced effect) which was reduced to near zero by a superimposed zero-disparity pattern and both patterns appeared as one surface. Adjacent vertical-size-disparity and zero-disparity patterns appeared as separate surfaces with a wide curved boundary. Overall-size disparity produced slant which was enhanced by a superimposed zero-disparity pattern and less so by a zero-disparity line, and induced more slant in a zero-disparity line than in a zero-disparity pattern. The results are discussed in terms of depth underestimation of isolated surfaces, depth enhancement, depth contrast, and the processing of deformation disparity.

scholarly journals Monitoring of Dry Bands and Discharge Activities at the Surface of Textured Insulators with AC Clean Fog Test Conditions

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2914
Author(s):  
Mohammed El Amine Slama ◽  
Maurizio Albano ◽  
Abderrahmane Manu Haddad ◽  
Ronald T. Waters ◽  
Oliver Cwikowski ◽  
...  
Keyword(s):  
Silicone Rubber ◽  
In Situ Monitoring ◽  
Pollution Level ◽  
Polluted Environment ◽  
Thermal Monitoring ◽  
Pollution Levels ◽  
Test Conditions ◽  
Preliminary Study ◽  
Dry Bands

The aim of this study is the presentation of the results of an in-lab comparative study of electrical and thermal monitoring of artificially polluted, HTV-textured silicone rubber insulators, with different pollution levels. This work is a preliminary study of an in-situ monitoring of 400 kV SiR textured in a polluted environment. The results showed that the rms leakage current magnitude and pulses, and the average dissipated power depended on the pollution levels and the dry-bands formation. The discharge activity and their nature are governed by the pollution level and the voltage. A differentiation and a quantification between dry-band discharge onset and dry-band arc inception is highlighted.

scholarly journals A Review of Some Recent Studies on Buoyancy Driven Flows in an Urban Environment

2014 ◽  
Vol 2014 ◽  
pp. 1-15 ◽  
Author(s):  
Bodhisatta Hajra
Keyword(s):  
Natural Convection ◽  
Water Channel ◽  
Field Measurements ◽  
Design Guidelines ◽  
Future Research ◽  
Channel Measurements ◽  
Cfd Modelling ◽  
Pollution Levels ◽  
Buoyancy Driven Flows ◽  
Building Walls

This paper reviews some recent studies (after 2000) pertaining to buoyancy driven flows in nature and thier use in reducing air pollution levels in a city (city ventilation). Natural convection flows occur due to the heating and cooling of various urban surfaces (e.g., mountain slopes), leading to upslope and downslope flows. Such flows can have a significant effect on city ventilation which has been the subject of study in the recent times due to increased pollution levels in a city. A major portion of the research reviewed here consists of natural convection flows occurring along mountain slopes, with a few studies devoted to flows along building walls. The studies discussed here primarily include field measurements and computational fluid dynamics (CFD) models. This review shows that for densely populated cities with high pollution levels, natural convection flows (mountain slope or building walls) can significantly aid the dispersion of pollutants. Additional studies in this area using CFD and water channel measurements can explain the physical processes involved in such flows and help improve CFD modelling. Future research should focus on a complete understanding of the mechanisms of buoyancy flows in nature and developing design guidelines for better planning of cities.

scholarly journals Friction Behavior of a Textured Surface against Several Materials under Dry and Lubricated Conditions

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5228
Author(s):  
Linqing Bai ◽  
Jianxin Sun ◽  
Pengcheng Zhang ◽  
Zulfiqar Ahmad Khan
Keyword(s):  
Friction And Wear ◽  
Friction Pair ◽  
Design Guidelines ◽  
Operating Conditions ◽  
Textured Surface ◽  
Friction Behavior ◽  
Positive Role ◽  
Wear Performance ◽  
Frictional Behavior ◽  
Texture Parameters

This paper reports research on the frictional behavior of a textured surface against several materials under dry and lubricated conditions, and this is aimed to provide design guidelines on the surface texturing for wide-ranging industrial applications. Experiments were performed on a tribo-tester with the facility of simulating A ball-on-plate model in reciprocating motion under dry, oil-lubricated, and water-lubricated conditions. To study the frictional behavior of textured SiC against various materials, three types of ball-bearing –elements, 52100 steel, silicon nitride (Si3N4), and polytetrafluoroethylene (PTFE), were used. Friction and wear performance of an un-textured surface and two types of widely used micro-scale texture surfaces, grooves and circular dimples, were examined and compared. The results demonstrated that the effect of surface textures on friction and wear performance is influenced by texture parameters and the materials of friction pairs. The circular-dimple texture and the groove texture, with certain texture parameters, played a positive role in improving friction and wear performance under specific operating conditions used in this research for SiC–steel and SiC–Si3N4 friction pairs; however, there was no friction and wear improvement for the textured SiC–PTFE friction pair. The results of this study offer an understanding and a knowledge base to enhance the performance of bearing elements in complex interacting systems.

Effects of Airfoil's Polar Data in the Stall Region on the Estimation of Darrieus Wind Turbine Performance

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
David Marten ◽  
Alessandro Bianchini ◽  
Georgios Pechlivanoglou ◽  
Francesco Balduzzi ◽  
Christian Navid Nayeri ◽  
...  
Keyword(s):  
Unsteady Aerodynamics ◽  
Vertical Axis ◽  
Design Guidelines ◽  
Operating Conditions ◽  
Performance Estimation ◽  
Simulation Methods ◽  
Computationally Efficient ◽  
Urban Context ◽  
Lift And Drag ◽  
Thrust And Torque

Interest in vertical-axis wind turbines (VAWTs) is experiencing a renaissance after most major research projects came to a standstill in the mid 1990s, in favor of conventional horizontal-axis turbines (HAWTs). Nowadays, the inherent advantages of the VAWT concept, especially in the Darrieus configuration, may outweigh their disadvantages in specific applications, like the urban context or floating platforms. To enable these concepts further, efficient, accurate, and robust aerodynamic prediction tools and design guidelines are needed for VAWTs, for which low-order simulation methods have not reached yet a maturity comparable to that of the blade element momentum theory for HAWTs' applications. The two computationally efficient methods that are presently capable of capturing the unsteady aerodynamics of Darrieus turbines are the double multiple streamtubes (DMS) theory, based on momentum balances, and the lifting line theory (LLT) coupled to a free vortex wake model. Both methods make use of tabulated lift and drag coefficients to compute the blade forces. Since the incidence angles range experienced by a VAWT blade is much wider than that of a HAWT blade, the accuracy of polars in describing the stall region and the transition toward the “thin plate like” behavior has a large effect on simulation results. This paper will demonstrate the importance of stall and poststall data handling in the performance estimation of Darrieus VAWTs. Using validated CFD simulations as a baseline, comparisons are provided for a blade in VAWT-like motion based on a DMS and a LLT code employing three sets of poststall data obtained from a wind tunnel campaign, XFoil predictions extrapolated with the Viterna–Corrigan model and a combination of them. The polar extrapolation influence on quasi-steady operating conditions is shown and azimuthal variations of thrust and torque are compared for exemplary tip-speed ratios (TSRs). In addition, the major relevance of a proper dynamic stall model into both the simulation methods is highlighted and discussed.

Spatial Representations as an Emergent Feature of Perceptual Processing

2010 ◽  
Vol 24 (3) ◽  
pp. 161-172 ◽  
Author(s):  
Edmund Wascher ◽  
C. Beste
Keyword(s):  
Common Ground ◽  
Event Related Potentials ◽  
Vertical Axis ◽  
Relevant Information ◽  
Sources Of Information ◽  
Integrated Network ◽  
Perceptual Maps ◽  
Emergent Feature ◽  
Related Potentials ◽  
Selection Of

Spatial selection of relevant information has been proposed to reflect an emergent feature of stimulus processing within an integrated network of perceptual areas. Stimulus-based and intention-based sources of information might converge in a common stage when spatial maps are generated. This approach appears to be inconsistent with the assumption of distinct mechanisms for stimulus-driven and top-down controlled attention. In two experiments, the common ground of stimulus-driven and intention-based attention was tested by means of event-related potentials (ERPs) in the human EEG. In both experiments, the processing of a single transient was compared to the selection of a physically comparable stimulus among distractors. While single transients evoked a spatially sensitive N1, the extraction of relevant information out of a more complex display was reflected in an N2pc. The high similarity of the spatial portion of these two components (Experiment 1), and the replication of this finding for the vertical axis (Experiment 2) indicate that these two ERP components might both reflect the spatial representation of relevant information as derived from the organization of perceptual maps, just at different points in time.

Sign in / Sign up

Export Citation Format

Share Document