Composite insulators are considered mature products and a broad range of insulator types is nowadays available, including line insulators, hollow-core insulators and apparatus insulators, for applications ranging from distribution voltages to the highest transmission voltages. This development has created a need to elaborate diagnostic methods and tools for determining the quality of composite insulators. A review on recognized insulator faults and methods for their detection is provided.

Diagnostic Methods for Outdoor Polymeric Insulators

We present a simple method for fabricating the superhydrophobic coatings on composite silicone rubber used for electrical outdoor applications. The coating is characterized by contact angles as high as 170° and is mechanically durable in contact with the aqueous phase. We discuss the impact of mechanical durability of the surface texture on the anti-icing performance of the coating on the basis of the experimental data on freezing delay of sessile aqueous droplets. A set of complementary data obtained in laboratory and outdoor experiments on freezing delay time, variation of wettability and practical work of adhesion for supercooled aqueous sessile droplets, impacting behavior of droplets at low negative temperatures, as well as the results of snow and ice accumulation in outdoor experiments indicate the very prospective icephobic properties of the developed coating.

Reinforced Superhydrophobic Coating on Silicone Rubber for Longstanding Anti-Icing Performance in Severe Conditions.

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

Capacitors in electrical and electronic systems composed of thin film dielectrics operate under extremely high electric fields. Dynamics of charge transport and relaxation are closely correlated to the energy storage properties and electrical degradation of thin film dielectrics for capacitive applications. In this paper, the dielectric relaxation properties of poly (vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer films are investigated over a broad frequency range from 10 mHz to 10 MHz and temperature range from −130 °C to 130 °C. The dielectric responses correlated to bulk and interfacial processes are clarified by varying the thickness and interfacial contact status of P(VDF-HFP) films. A low frequency process originating from the quasi-DC (QDC) process and a dielectric dispersion process correlated to the interfacial polarization are identified based on the Dissado-Hill dielectric response model and the equivalent circuit analysis. The high permittivity and high operation electric field of P(VDF-HFP) for capacitive energy storage give rise to improved blocking capacitance associated with the interface, suggesting the enhanced interfacial polarization. This work provides insights into the bulk and interface charge dynamics of polymer thin film dielectrics.

Interfacial and Bulk Polarization of P(VDF-HFP) Investigated by Dielectric Spectroscopy

The invention discloses a general type runner flange testing device used for a composite insulator. The general type runner flange testing device comprises a support device, a transmission shaft, a driving device, four first flange plates, four insulators, a high-voltage electrode and a water tank, wherein the support device comprises a front support and a rear support which are spaced along the back-and-forth direction; the transmission shaft is respectively connected with the front support and the rear support in a pivoting mode so as to pivot relative to the front support and the rear support; each flange plate is connected with the peripheral wall of the transmission shaft through a connecting column, and the four first flange plates are distributed at equal intervals and are distributed on the same circle; the four insulators correspond to the first flange plates in a one-to-one correspondence mode. According to the general type runner flange testing device used for the composite insulator disclosed by the invention, the insulators are connected the composite insulator by utilizing a first flange plate, the general type runner flange testing device can be suitable for runner flange tests of the composite insulator to be detected with various diameters, and test support is provided for intensively studying the tracking and erosion resistance of the composite insulator.

General type runner flange testing device used for composite insulator

Temperature dependence and correlation of polarization processes in P(VDF-HFP) films

As the material for shed and sheath of composite insulators, HTV silicone rubber faces multiple stresses in the serving environment, in which water permeation may lead to degradation and harm the cores. This research studied in the dielectric response of HTV silicone rubber samples which have been immersed into deionized water, and analyzed the test results with Dissado-Hill loss peak model and QDC model. Both real and imaginary parts of the dielectric response increased after immersed for 400h. The fitting results showed that the QDC phenomenon was more obvious after long time immersion. Water promoted the number of charges which participated in the hopping process, and offered path for the hopping process in QDC. Meanwhile, water invading made the interfaces loose and led to disorder of the structure. These results prove that water permeation is highly likely to be the reason of chalking on the shed and sheath of composite insulators.

Impact of Water Permeation on the Dielectric Response of HTV Silicone Rubber

Insulators, especially silicone rubber (SR) based composite insulators, are of great significance for overhead transmission lines. SR composite insulators show great advantage on light weight, convenience of maintenance and excellent hydrophobicity. Besides, the ability of hydrophobic transfer makes it the best choice for anti-pollution flashover, and thus make it promising to develop SR super-hydrophobicity (SH) material. Meanwhile, charges will accumulate on the insulator surface under DC high voltage, which would bring about more contamination, distort the electric field distribution and affect the hydrophobicity of material. In this paper, SH samples of SR with different micro-structures were prepared. An electrode system was designed to inject charges to the sample surfaces. Then DC voltages of different polarities and amplitudes were applied to investigate the dissipation characteristics of surface charge on SH surfaces. Also, the influence of charge accumulation on hydrophobicity was investigated by the measurement of surface potential and contact angle. The correlation between surface charge dynamics and material properties was revealed according to the results, including resistivity and the treating process of SH surfaces.

Xidong Liang

Papers

Interfacial and Bulk Polarization of P(VDF-HFP) Investigated by Dielectric Spectroscopy

General type runner flange testing device used for composite insulator

Temperature dependence and correlation of polarization processes in P(VDF-HFP) films

Impact of Water Permeation on the Dielectric Response of HTV Silicone Rubber

Characteristics of Charge Dissipation on Super-Hydrophobic Surface of Silicone Rubber and Its Influence on Hydrophobicity