Intelligent overheating fault diagnosis for overhead transmission line using semantic segmentation

The strain clamps and leading wires are important components that connect conductors on overhead transmission lines and conduct current.During operation,poor contact between these components can cause abnormal overheating,leading to electric failures and threatening power system reliability.Recently,the use of unmanned aerial vehicles equipped with infrared thermal imagers for strain clamp and leading wire maintenance has become increasingly popular.Deep learning-based image recognition shows promising prospects for intelligent fault diagnosis of overheating faults.A pre-treatment method is proposed based on dynamic histogram equalisation to enhance the contrast of infrared images.The DeepLab v3+network,loss function,and existing networks with different backbones are compared.The DeepLab v3+network with ResNet101 and convolutional block attention module added,and the Focal Loss function achieved the highest performance with an average pixel accuracy of 0.614,an average intersection over union(AIoU)of 0.567,an F1 score of 0.644,and a frequency weighted intersection over union of 0.594 on the test set.The optimised Atrous rates has increased the AIoU by 12.91%.Moreover,an intelligent diagnosis scheme for evaluating the defect state of the strain clamps and leading wires is proposed and which achieves a diagnostic accuracy of 91.0%.

Intelligent Breakage Assessment of Composite Insulators on Overhead Transmission Lines by Ellipse Detection Based on IRHT

With the development of unmanned aerial vehicle(UAV)technology,visible images are playing an important role in the maintenance of power systems.To achieve the shed breakage evaluation of composite insulators by UAV visible images,an intelligent fault assessment method is proposed.First,the composite insulators in visible light images are identified by Faster-RCNN.After image preprocessing,the image is enhanced and the noise is removed.Then,a canny operator is used to extract the edge of the sheds.An Improved Randomized Hough Transform(IRHT)is used to detect the ellipses in the edge image.The parameters of the detected ellipse,length of major axes and minor axes,center coordinates and deflection angle of major axes,are used to realize the segmentation of the composite insulator.Finally,the number of pixel points in the ellipse and the distance between the points and the ellipse boundary are used to judge whether there are breakage or cracks on the sheds.The area ratio of the breakage to the whole shed is calculated based on the number of pixel points inside the broken area.This method can be realized without a large amount of training dataset of the specific fault type and provides a technical basis for the online fault assessment of a composite insulator on overhead transmission lines.

Self‐adaptive electrostatic discharge performance of ZnO microvaristors doped silicone rubber composites

With the increase in applied voltage and the decrease in volume,integrated electronic modules have become electrostatic sensitive.ZnO microvaristors doped silicone rubber(SiR)composite,with electric field‐dependent conductivity,shows promising prospects for solving the electrostatic problem.In this study,20 vol%to 50 vol%ZnO/SiR composite films,filled with 10–30μm ZnO microvaristors,were prepared and put into the test of electrostatic discharge.Compared with the insulating and conducting materials,ZnO/SiR composites achieve the lowest initial voltage and a short time constant of electrostatic discharge.With the increase of ZnO microvaristors volume fraction,from 20%to 50%,the initial voltage and the time constant of electrostatic discharge drop from 1.78 to 0.72 kV and 3.1 ms to 0.4μs.When the ZnO volume fraction is higher than 30%,there is no residual voltage after 0.1 s.To explore the reason behind different electrostatic discharge performances of the ZnO/SiR composites,the conductivities of the com-posites were measured.It is found that the break‐over voltage of the composite drops with the increase in the ZnO microvaristors volume fraction.When a high voltage im-pulse is applied on the ZnO/SiR film,the composite will turn to the conducting state and release the electrostatic charge adaptively so that the initial voltage can be controlled.This work supplies a novel electrostatic discharge idea for electric and electronic devices.

Technique for Order Preference by Similarity to an Ideal Solution-based comprehensive health assessment of composite insulators for overhead transmission lines

There are a lot of quantitative performance characterisation methods for composite insulators.However,how to apply the characterisation methods with different dimensions to comprehensively assess the health state of composite insulators remains a big problem for operators and researchers.A comprehensive health assessment model for composite insulators based on the Technique for Order Preference by Similarity to an Ideal Solution(TOPSIS)method is proposed in this study.Fourteen composite insulators from four regions in Yunnan Province,China,and five quantitative characterisation indicators of the insulators,namely hardness,hydrophobicity,loss of hydrophobicity,recovery of hydrophobicity,and trap charge,are selected to verify the model.The results show that the Pearson correlation coefficient of the TOPSIS-based comprehensive health score with operating time is 0.72,which is better than the other single indicator.By introducing the operating time into the TOPSIS-based model,we can also obtain the ageing resistance performance of the composite insulator.This work provides a new idea to assess the health state and ageing performance of composite insulators.

Review on the Characteristics,Heating Sources and Evolutionary Processes of the Operating Composite Insulators with Abnormal Temperature Rise

This paper reviews the research progress on abnormal temperature rise(ATR)of composite insulators.The ATR of composite insulators can be divided into two types,point-form temperature rise(PFTR)and bar-form temperature rise(BFTR).The composite insulators with PFTR only show significant temperature rise at high relative humidity(RH)(>70%),and the temperature rise is located in the area that is 20 cm above the metal end-fitting.In a low humidity environment(<30%),there is little temperature rise(<1.0 K).The polarization loss on the surface of the silicone rubber housing under an AC electric field after moisture absorption is the main heating source.Corona discharge in high RH causes surface degradation of the silicone rubber.The composite insulators with BFTR shows significant temperature rise at both high(>70%)and low(<30%)RH.The temperature rise could reach more than 10◦C and the temperature rise area is wider,extending from the high-voltage end to several shed units at the lowvoltage side.And the glass fiber reinforced plastic(GRP)core in the composite insulator is found to be corroded.The heating energy is supplied by both conductance loss and polarization loss of the corroded GRP core.The decay-like degradation of the GRP core is caused by the combination of damp conditions,high electric field,discharge,mechanical load,et al.and may evolve into a decay-like fracture of the composite insulator.The preventive methods concerning quality control,structure optimization,material modification and operational strategy are presented.It is suggested that when PFTR is detected on the composite insulator,the inspection period of the insulator should be properly shortened.The composite insulator should be replaced as soon as the BFTR was detected.

Non‐linearly conductive ZnO microvaristors/epoxy resin composite prepared by wet winding with polyester fibre cloth

ZnO microvaristors/epoxy resin composite has drawn great attention from academia and industry for its adjustable non‐linear conductivity,high mechanical strength,and good ageing resistance.However,the sedimentation of ZnO microvaristors in epoxy resin during preparation is the key problem,which limits its application in engineering.In this study,a novel method of wet winding with polyester fibre cloth is proposed to prepare the ZnO microvaristors/epoxy resin composite.The anti‐settling effect of ZnO micro-varistors in the composite is verified by scanning electron microscopy(SEM)and thermal gravimetric analysis(TGA).The microstructure shows that ZnO microvaristors distribute uniformly in the composite,and the content difference of ZnO microvaristors at the top and bottom part is only 0.4%.The composite shows typical non‐linear conductivity,and the threshold electric field and the non‐linear coefficient decrease with the content of ZnO microvaristors,while the conductivity in the insulating state shows an increasing trend.To verify the field grading effect of the composite with non‐linear conductivity(CNC),a finite element model of a needle‐plate electrode,simulating the condition of a conductive tip in a solid insulated system,is set up.CNC can adaptively grade the electric field,which reduces the surface electric field of the needle tip by 86.6%and the highest electric field in the system by 82.1%.This wet winding method solidifies the industrial application of CNC in high‐voltage power equipment.

Environment-friendly Insulating Gases for HVDC Gas-insulated Transmission Lines

Environment-friendly gas insulating mediums adapted to a DC gas-insulated transmission line(GIL)electric field condition is the key to the next generation of Environment-friendly HVDC GILs.In this paper,we review the literature on sulfur hexafluoride(SF6)alternatives including the scientific understanding,control,and implementation of gas-solid systems in this type of power transmission.First,the structure-activity relationship between the molecular structure and physico-chemical properties of Environment-friendly insulating gases is presented.Then,the search and prediction of important physicochemical properties of gases are summarized.Subsequently,in view of the potential of environmental friendly insulating gases,the swarm parameters of gas discharge and breakdown properties in a quasi-uniform field,inhomogeneous field,and at the gas-solid interface,that need to be taken into account with industrialized DC GILs are discussed.The latest research progress on insulation characteristics,especially the polarity effect in DC gas-solid insulation systems,the sensitivity to the electrode surface state,and the non-uniformity of the electric field,and the influence of metal particles and their variation with air pressure,is highlighted.In addition,the heat transfer characteristics of insulating gases,related to DC GIL transmission with a large current-carrying capacity and the influence of alternative gases on the heat transfer characteristics are described.Finally,aiming at solving the contradiction of low environmental impact,high dielectric strength and low liquefaction temperatures in the selection of alternative gases,an coordinated regulation model for Environment-friendly gases in DC GILs is established.Considerations for future work on this topic are also presented.

Design of adaptive bushing based on field grading materials

Electrical bushings,as important power system components,are critical to the reliability of power systems.The capacitance-graded bushing is a type of high voltage bushing that is most commonly used in current power systems.However,the limitations of and problems with capacitance-graded bushings are exposed when the operating voltage level increases.A new direct current wall bushing with adaptive field grading materials is proposed,based on the core features of the problem that the bushing is intended to solve.The main insulation structure of the proposed DC wall bushing with adaptive field grading materials comprises three parts:a field grading layer,a current limiting layer and an electrode extension layer.The proposed bushing has characteristics that include a simple structure,small size and environmental friendliness,and it also meets the re-quirements of existing power systems.The proposed bushing also conforms to the intended development direction for future power equipment and will aid in the devel-opment of power systems for operation at higher voltages.

高压下新型超硬富硼氮化物

富硼化合物通常为潜在的超硬材料,尽管之前的研究提出了不同晶型的BN超硬材料,但尚未发现超硬的富硼氮化物.本文采用基于粒子群优化算法的结构预测方法,结合第一性原理计算,对富硼氮化物在压力下的稳定成分及结构进行系统研究.结果表明,在B4N、B6N和B8N中,硼原子都能够形成B12二十面体.在0–20 GPa压力范围内,B6N是热力学稳定的,而B4N和B8N是亚稳的.电子性质计算表明,预测的Cmca B6N和Immm B6N为半导体,其他均为金属.声子和弹性常数计算表明,所有预测结构都具有动力学稳定性和机械稳定性.值得关注的是,B4N和B6N的维氏硬度分别为45和42 GPa,表明其为潜在的超硬材料.此研究丰富了B-N体系相图,并为实验上探索超硬材料提供了丰富的理论指导.