Failure of insulators leads to failure of transmission system and causes heavy loss to the power sector. This has necessitated helicopter inspection on transmission line. Therefore, localizing insulators in collected aerial image is an essential step for automatic fault detection. This paper proposes a localization method of multiple insulators with different angles in complex aerial image based on Orientation Angle Detection and Binary Shape Prior Knowledge (OAD-BSPK). Detect possible orientation angles of insulators preliminarily. For each possible angle, reserve insulator by its binary shape prior knowledge. Traverse all the possible angles, and multiple insulators can be localized in aerial image finally. This paper uses a large number of real aerial captured images as experimental images. The results show that this method can localize multiple insulators with different orientation angles in complex aerial image, and has higher positioning precision, lower computational complexity and lower time consuming compared with existing methods. This method can meet the requirements of insulators’ real-time and accurate localization.

Localization of multiple insulators by orientation angle detection and binary shape prior knowledge

In recent years, a new kind of abnormal fracture phenomena of composite insulator occurred in high voltage transmission lines in several countries, which was totally different from brittle fracture and normal fracture. According to the general characteristic features of the fracture, this type of failure was named decay-like fracture of composite insulator by the author. In this paper, a decay-like fractured composite insulator was investigated and microscopic physic-chemical properties of decay-like fractured Fiber Reinforced Plastic (FRP) core rod were analyzed. Scanning Electron Microscope (SEM), Thermal Gravimetric Analysis (TGA) and Fourier Transform Infrared (FTIR) Spectroscopy methods were employed to explain the microscopic morphology characteristics and chemical component changes of decay-like fractured composite insulator, and to further explain the reasons for the name of decay-like fracture in terms of "crisp" and "decay-like". The main microscopic feature of decay-like fracture is the degradation and deterioration of the epoxy resin matrix in FRP rod. The mechanism of decay-like fracture of composite insulator could be summarized as follows. Due to the liquids penetration into the sheath-core interface, hydrolysis of silane coupling agent with bad quality leads to poor adhesion strength and interface voids, which results in distortion of electric field at the sheath-core interface. Under the combined action of damp condition and high electric field, discharge and current appear along the FRP rod surface. Epoxy resin matrix is eroded in the presence of discharge and current, and then is soften, melt, evaporated. Meanwhile, ion-exchange and hydrolysis process happen between glass fibers under the combined action of mechanical stress and nitric acid produced by discharge in the presence of moisture. Fiber-resin interface in FRP rod is separated owing to the erosion of epoxy resin. The degradation direction of the decay-like fracture is from outside to inside of FRP rod, and the interface between silicone rubber sheath and FRP rod is confirmed to be the initial deterioration area of the decay-like fracture. The criterion to distinguish the differences between the decay-like fracture, brittle fracture and normal fracture depends on whether the epoxy resin matrix is degraded and deteriorated or not.

Decay-like fracture mechanism of silicone rubber composite insulator

Outdoor insulators are often subject to corona discharges and the problem is becoming more prevalent with the increasing use of higher transmission voltage levels. For polymeric insulators, exposure to such discharges can alter the chemical structure of basic polymer and degrade surface properties. This paper investigates the effect of micro and/or nano fillers in silicone rubber composites in suppressing such damage. Four different types of samples are fabricated: pristine silicone rubber (PR), 30wt% micron–sized silica/silicone rubber (MC), 27.5wt% micron + 2.5wt% nano silica/silicone rubber (NMC), and 5wt% nano silica/silicone rubber (NC) composites. Samples are exposed to AC corona using a needle to ground-plane electrode setup. Experimental results are analyzed based on five different measurement methods: phase-resolved partial discharge (PD), hydrophobicity loss-recovery, Scanning Electron Microscopy (SEM), Surface roughness and Fourier Transform Infrared Spectroscopy (FTIR). Results indicate that NC shows a strong resistance to partial discharges and hydrophobicity loss. In the area below the needle tip, higher hydrophobicity loss and higher recovery are observed as compared to the vicinity region. Variations in surface roughness, appearance of crackles, voids, pits, surface splitting into blocky structures and damages to chemical structure of silicone rubber are appreciably retarded in NC as compared to PR, MC and NMC. Based on NMC results, it is found that addition of nano–sized silica can be an attractive approach to improve the corona resistance of micron–sized silica filled silicone rubber.

Performance of silicone rubber composites with SiO 2 micro/nano-filler under AC corona discharge

Direct replication of micro-nanostructures in the fabrication of superhydrophobic silicone rubber surfaces by compression molding

https://iopscience.iop.org/article/10.1088/2053-1591/ab3f0d/pdf

Aging of silicone rubber-based composite insulators under multi-stressed conditions: an overview

In this paper, the permeation properties of three types of liquids into HTV silicone rubber with different Alumina Tri-hydrate (ATH) contents had been investigated by weight gain experiments. The influence of differing exposure conditions on the diffusion into silicone rubber, in particular the effect of solution type, solution concentration, and test temperature were explored. Experimental results indicated that the liquids permeation into silicone rubber obeyed anomalous diffusion ways instead of the Fick diffusion model. Moreover, higher temperature would accelerate the permeation process, and silicone rubber with higher ATH content absorbed more liquids than that with lower ATH content. Furthermore, the material properties of silicone rubber before and after liquid permeation were examined using Fourier infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively. The permeation mechanisms and process were discussed in depth by combining the weight gain experiment results and the material properties analyses.

Investigation on permeation properties of liquids into HTV silicone rubber materials

In recent years, a new type of composite insulator mechanical failure appeared in high voltage transmission lines, which is a type of severe accident for power system, but only few studies on it have been reported all over the world. In this paper, this type of failure was named Decay-like Fracture by summarizing and analyzing the general features, and the decay-like fracture of composite insulator was treated and studied as a new type of composite insulator mechanical failure. By analyzing some field failed composite insulators in China, main features of decay-like fracture were then summarized. The fracture spot of decay-like fractured insulator became crisp and looked like decayed wood. The mechanisms of the normal fracture and brittle fracture of composite insulator cannot explain decay-like fracture, and boron-free Fiber Reinforced Plastic (FRP) core which has been widely used to prevent brittle fracture could not prevent decay-like fracture. Decay-like fracture is not a pure mechanical failure. The discharging and surface micro current on the core surface would finally lead to mechanical fracture of composite insulator. But the process and mechanism of decay-like fracture still need further researches.

Failure analysis of decay-like fracture of composite insulator

This study utilized a multi-needle corona electrode system to investigate the influence of AC and DC coronas on the surface properties of high temperature vulcanized (HTV) silicone rubber. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) analysis were performed to characterize the chemical structure and hydrophobicity changes in state of the silicone rubber surface after corona exposure. The results indicated that the effects of AC corona were greater than that of DC corona, and the effects of negative DC corona were slightly greater than that of positive DC corona. XPS results showed that the C elemental content on the silicone rubber surface decreased, whereas the O elemental content increased. High-resolution scan on Si 2p XPS spectra proved that surface oxidation occurred during corona exposure and caused the high binding energies of Si atoms and silica-like layer. High-resolution C 1s XPS spectra showed that corona exposure destroyed the Si-CH3 groups on the surface. Some C-O and C=O bonds appeared following the corona exposure. High-resolution O 1s XPS spectra confirmed the formation of Si-OH groups and chemically absorbed water, which was ignored in the past research. Chemically absorbed water was detected as one of the essential factors that caused the loss of hydrophobicity of silicone rubber after corona exposure, together with Si-OH groups and silica-like layer.

Effects of AC and DC corona on the surface properties of silicone rubber: Characterization by contact angle measurements and XPS high resolution scan

In this first part of a review on high voltage composite suspension insulators, the fracture morphology characteristics of all known fracture modes including normal fracture, brittle fracture, and decay-like fracture are discussed.

Comparative Investigation on Fracture of Suspension High Voltage Composite Insulators: A Review—Part I: Fracture Morphology Characteristics

Previous studies on brittle fracture of composite insulator were concluded, and unanswered questions were analyzed. Almost all the previous studies focus on the source of corrosion medium (the acid) and the mechanical load in brittle fracture, but the stress concentration of stress corrosion fracture was neglected. Sand paper polishing in the manufacturing process of composite insulator may lead to surface micro-cracks with the depth deeper than 30 ?m-40 ?m on the fiber reinforced plastic (FRP) rod surface. Stress concentration caused by surface micro-crack in FRP rod and its influence on brittle fracture was noticed in experimental study. The importance of the surface micro-crack in FRP rod was verified by a series of experimental studies. An explanation of the randomness of brittle fracture in composite insulator was put forward. Finally, the actions that should be taken to prevent brittle fracture of composite insulator were emphasized.

Jiafu Wang

Papers

Investigation on permeation properties of liquids into HTV silicone rubber materials

Failure analysis of decay-like fracture of composite insulator

Effects of AC and DC corona on the surface properties of silicone rubber: Characterization by contact angle measurements and XPS high resolution scan

Comparative Investigation on Fracture of Suspension High Voltage Composite Insulators: A Review—Part I: Fracture Morphology Characteristics

Surface micro-crack initiated brittle fracture in fiber reinforced plastic rod of composite insulator