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The accumulation of insulator surface contamination is closely related to the distribution of flow field around the insulator. In order to study the unevenness of the insulator surface contamination, a three-unit lxy-160 insulator is selected. Based on the principle of fluid mechanics, the fluid movement state on the insulator surface is determined by the calculation of Reynolds number and boundary layer, then the flow field distribution around the insulator is obtained. On this basis, the artificial contamination test and numerical simulation are carried out to study the characteristics of contamination uneven distribution on the insulator surface. The results show that when the wind speed is 3–7 m/s and the particle diameter is 1–60 µm, there is obvious boundary layer separation phenomenon, and the flow state before the separation point is laminar, while the flow state behind the separation point is turbulent. From top to bottom, the degree of accumulation on each insulator is different, and the contamination on the windward and leeward sides are unevenly distributed in a fan shape. The increment of wind speed as well as particle diameter will aggravate the unevenness of the contamination.

Icicles generated on the insulator sheds will constantly shorten the insulating gap distance between adjacent sheds as growth, thereby inducing significant decrease in electrical insulation of the insulators, icicle bridging even threatening the operating security of power systems. In order to evaluate whether the ice-covered insulator needs to deicing or the icicles bring in potential dangers, a study on detection and condition assessment of icicle bridging for ice-covered suspension glass insulator by image analysis is proposed in this article. First, the initial icicles regions are obtained by the local variation threshold segmentation algorithm based on the optimized texture energy image. Second, the insulator sheds are segmented and extracted based on the normalized color difference operator, and then the complete icicles regions are obtained through the image difference and postprocessing. Finally, the icicle length is calculated by finding its smallest axis-parallel enclosing rectangle, and two adjacent insulator sheds spacing which is calculated by ellipse fitting is used as bridging threshold, so the condition of icicle bridging can be defined as the safe, observation, and danger. The results demonstrate that the icicles can be effectively enhanced and accurately segmented by the presented method in this article, and the icicle bridging condition of ice-covered insulator can be assessed with average detection accuracy of 92.2% and average time consumption of 3.910 s, by which the safe operation of ice-covered insulator can be monitored and guaranteed.

The series of physical processes contained in the corona layer is the source of space ions formed by the corona discharge of the high-voltage AC line. However, since these physical processes are difficult to calculate accurately and the corona layer thickness is usually small, the corona layer is ignored in the published literature on the corona discharge of the AC line, and the ions are considered to be emitted directly from the conductor surface. In this paper, the distribution area of the charged particles is divided into the corona plasma region and the unipolar drift region. A mathematical physical model of the photoionization and photoemission, which sustain self-sustaining discharge in the positive and negative half-cycle of corona plasma region of the AC conductor in dry air, are established. The influence of the ions generated in the previous cycle is also considered in the numerical simulation process. Finally, a complete microscopic physical model describing the corona discharge of the AC conductor under dry air is established. The validity of the physical model proposed in this paper is demonstrated by comparison with experimental results reported in the literature. Through the numerical simulation of the ion flow field of positive and negative half-cycle and the corona current, the physical process of the corona discharge around the AC line is better understood and analysed. Further positive and negative half-cycle charged particle motion and corona plasma regions were compared and analyzed. This work provides a brand new mathematical physics method for understanding and applying AC corona discharge.

Icicle will cause serious distortion of insulator electric field, weaken its voltage strength, and easily cause insulator flashover. Previous studies have shown that the longer the length of icicles on insulator, the greater the possibility of electric flashover. Then, it is of great theoretical significance and practical value to study the image identification technology of icicle length of iced insulators. Firstly, the growth mechanism and structural characteristics of insulator icicles are discussed in this paper, and the image acquisition method of iced insulator is discussed. Secondly, the methods of saliency detection and color feature analysis are used to extract the region of icicle and insulator sheds respectively, then, the icicle structure on insulator is obtained by the difference calculation of above two images. Meanwhile, the pixel curve of the iced insulator image is processed by Fourier transform, and the reference size of insulators icicle is obtained by calculating the length of the shed spacing. Finally, a practical case about iced insulators in substations is analyzed in detail, which proves the effectiveness of the method proposed in this paper.

The thermal de-icing by Joule effect is a mostly valid way to prevent transmission-lines from the severe ice storm. A model was put forward to simulate the critical ice-melting current on iced conductor. Based on this model, the value of critical ice-melting current was calculated with various parameters, some of which were ignored in the earlier literatures, such as ice-layer heat conductivity, wind attack angle, and icing section shape. The results of the experiment and simulation show that the critical ice-melting current increase with wind speed, wind attack angle, and ice-layer heat conductivity, but decrease rapidly with ambient temperature and liquid water content. Moreover, the maximum difference between the results of simulation and experiment is about 9%, thus this model can be employed to estimate the engineering parameters in practical thermal de-icing projects.

Hydrophobicity of the composite insulators is a parameter which is closely related to the insulation properties. In order to determine whether the insulator in the transmission line needs to be withdrawn, it is necessary to objectively and accurately determine the hydrophobicity grade of the composite insulator. The study on hydrophobicity detection of composite insulators of transmission lines by image analysis is proposed in this paper, by which the hydrophobicity of composite insulators can be measured timely. The grayscale, median filtering, and histogram equalization of the hydrophobic images are fulfilled sequentially, and the water drops (or water marks) region is segmented by binary large object analysis and four parameters related to water repellency are extracted. In addition, the improved support vector machine algorithm is adopted to calculate the hydrophobicity of composite insulators. The results show that seven typical hydrophobic levels of insulators can be recognized by the proposed hydrophobicity detection method whose accuracy is more than 91%.

Gas Insulated Switchgear (GIS) is a complete set of switchgear, such as circuit breaker, disconnector, bus bar, which enclosed in a metal shell filled with SF 6 gas grounding. The presence of internal metal particles will cause partial discharge of GIS, leading to insulation breakdown. The main purpose of this paper is to study the particle movement rules of different shapes and sizes based on different types of voltage, so as to determine a kind of fault map. The fault map is used to estimate the shape and size of the metal particles that cause GIS partial discharge. Based on this purpose, the movement of metal particles under the action of high voltage AC, DC and pulse signals are simulated by electric field simulation and mechanical analysis. The results show that there is no regularity in the movement of particles under AC and DC, but there is regularity in the movement of particles under pulse voltage. Different types and sizes of particles have different trajectories. The movement height of particles is directly proportional to the length of particles, the applied voltage and inversely proportional to the half diameter of particles.

To evaluate the aging state of composite insulating materials quickly and accurately, this paper proposes a method based on polarization/depolarization current method. High polymer epoxy is selected as the research object. The UV aging test is performed on epoxy materials, and the polarization/depolarization current method is used to detect the aging state of the materials. Through the analysis of the polarization and depolarization current curve, the initial value, stable value and turning time of polarization and depolarization current are extracted as the characteristics of the aging state of the epoxy material. Comparing the polarization/depolarization current curves and their characteristic values of materials with different aging degrees, it can be found that the initial value, stable value and turning time of polarization and depolarization current are closely related to the aging degree of materials in the polarization and depolarization stages. The results show the more serious the aging of epoxy materials, the greater the polarization and depolarization current. The results show that the polarization / depolarization current method can effectively evaluate the aging characteristics of composite insulator.

Designing an outdoor insulation-appropriate material architecture with superior surface weatherability, hydrophobicity transfer, and electrical and mechanical properties would play an essential role in enhancing the security operations of power systems. In this work, a cycloaliphatic epoxy resin (CEP) was modified with organofluorine and organosilicon to introduce functional groups to improve its surface properties. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectral analysis showed that these functional groups were successfully introduced into the modified CEP. The characteristics of the modified CEP were assessed in terms of weather resistance, mechanical properties and hydrophobicity. The results show that the modified CEP composite surface integrates the complementary characteristics of multiple components, thereby greatly improving the surface impact toughness, hydrophobicity and weatherability. The hydrophobicity migration of the new composite was tested. The results show that a large number of hydrophobic groups (Si−CH3) migrate to the sample surface, causing self-healing of hydrophobicity, which helps prevent pollution flashover. In addition, electric insulation tests were conducted on modified CEPs with different contents of micro-nanometre fillers without affecting the mechanical properties of the composite system. The test results revealed the best combination of inorganic fillers to improve the insulation performance. The micromorphology and mechanism of interaction between the CEP-based composite and nanoparticles were analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermally stimulated depolarization current (TSDC) and broadband dielectric spectroscopy. This work provides an invaluable guideline for the design of outdoor insulation composite materials.

The capacitive method is considered to be a suitable icing-detection technology, but the lack of fundamental parameters restricts the development of icing-detection sensors. In this paper, an artificial icing laboratory, a capacitive sensor, and some simulation conductors have been designed for obtaining the artificial icing samples. Subsequently, the same characteristic values of artificial icing have been measured by an LCR device, under a selected frequency. This research found that the value of the icing dielectric constant closely correlated with its density, internal sublayer, and the test temperature. Finally, a fitting formula has been presented for calculating the relative dielectric constant, which may provide some important reference value for the design of icing-detection sensors.

The traditional HTV silicone rubber composite insulators are widely used in power transmission lines at home and abroad due to their excellent hydrophobicity and hydrophobicity. However, with the development of UHV, more and more transmission lines need to cross strong ultraviolet radiation, strong wind sand and bird pecking regions. In this kind of bad climate regions, it is very easy to cause the decline of the external insulation performance of traditional HTV silicone rubber insulators and the damage of materials. Aiming at this situation and combining with the ultraviolet radiation characteristics of high altitude area, UCV is used as ultraviolet light source, and the high polymer composite insulators with strong resistance to ultraviolet, climate and stable mechanical properties provided by the global energy economic institute are selected as the research object. The purpose is to study the aging characteristics of new composite insulators in the high ultraviolet radiation area of the Northwest Plateau. The results show that under the continuous irradiation of UCV short wave ultraviolet light, the tensile strength and hardness of the epoxy material are much higher than that of the silicone rubber. It has better toughness and has reached the purpose of bird proof and tread resistance. However, hydrophobicity is slightly less than silicone rubber material, but compared with traditional epoxy materials, it has made considerable progress to meet outdoor operation requirements.

Transmission lines are affected by Aeolian vibration, which causes strands to break and eventually causes an entire line to break. In this paper, a method for monitoring strand breaking based on modal identification is proposed. First, the natural frequency variation of a conductor caused by strand breakage is analyzed, and a modal experiment of the LGJ-95/15 conductor is conducted. The measurement results show that the natural frequencies of the conductor decrease with an increasing number of broken strands. Next, a monitoring system incorporating a fiber Bragg grating (FBG)-based accelerometer is designed in detail. The FBG sensor is mounted on the conductor to measure the vibration signal. A wind speed sensor is used to measure the wind speed signal and is installed on the tower. An analyzer is also installed on the tower to calculate the natural frequencies, and the data are sent to the monitoring center via 3G. Finally, a monitoring system is tested on a 110 kV experimental transmission line, and the short-time Fourier transform (STFT) method and stochastic subspace identification (SSI) method are used to identify the natural frequencies of the conductor vibration. The experimental results show that SSI analysis provides a higher precision than does STFT and can extract the natural frequency under various wind speeds as an effective basis for discriminating between broken strands.

Composite insulator has been widely used in high-voltage power system; besides, its service life is getting longer and longer. Accordingly, the aging of the composite insulator has been paid more and more attention by the people, and how to comprehensive evaluate the aging state of composite insulator in service is great important to ensure the reliability of the transmission line. In this paper, the nodal discontinuous Galerkin method is for the first time used to analyze the electric field distribution on the surface of composite insulator, and the deformation of composite insulator is analyzed by the finite element method. Based on the numerical analysis for the surface electric field distribution and deformation of the composite insulator, the operation state of which is evaluated, and then it will help establishing a new method for evaluating the operation state of composite insulators and high-voltage tower, and a collective evaluating model for completing the aging properties of composite insulators. Finally, an on-line monitoring method is designed to monitor the deformation of the insulator by the strain gauge embedded in the composite insulator surface, thus monitoring the running state of insulator strings in real time.

In view of the problems of electromagnetic interference, power supply instability and short service life of existing transmission line condition monitoring devices, this paper develops an integrated condition monitoring system of transmission lines based on fiber bragg grating sensors. This system uses fiber bragg grating strain sensor, tension sensor, temperature sensor and vibration sensor to measure the tower strain, wire tension, wire temperature and Aeolian vibration, and sends the optical signals to the fiber bragg grating demodulator of the substation through OPGW. This system can realize the passive measurement of the running condition of the wire, and there will be no power supply problems. In addition, combining with the characteristics of anti-electromagnetic interference and high precision of the fiber bragg grating sensors, the stability and reliability of the system are improved.

The WC-Co composite nano-coatings bonded strongly with steel substrate has been made by vacuum fusion sintering (VFS). Diffusion plays a crucial role in VFS processes, of which the atoms diffusion nearby interface is a vital variable which influences the interfacial bond strength. The atoms diffusion during the vacuum fusion sintering (VFS) process was firstly studied by molecular dynamics and by Fick second law of diffusion. The three-dimensional MD model was built, by which the atoms diffusion, atoms migration contrail and the VFS process were simulated. The concentration distribution of some components were measured by the electrical probe, and the microstructure and morphology of VFS nano-coatings were observed and analyzed by SEM, X-ray diffraction meter and micro-hardness instrument. Combined with the experimental results, diffusion coefficient of every element was calculated in diffusion dynamics.