To address the challenge of accurately determining the saturation state induced by transformer DC bias, we propose a combined method for analyzing the DC bias of the transformer using vibration signals. This method employs the complementary ensemble empirical mode decomposition (CEEMD) to preprocess the vibration signals and fuzzy entropy (FuzzyEn) to assess the degree of DC bias. The optimal measurement point of the transformer is determined through transformer mechanical analysis. Subsequently, a vibration test. experimental platform is established to capture vibration signals at five distinct points on the transformer shell and core. These signals are then subjected to CEEMD for reconstruction, enabling the determination of the degree of DC bias. This assessment is based on fuzzy entropy values and difference curve analysis. The results demonstrate that the FuzzyEn value, serving as an indicator of the iron core's saturation due to DC bias, effectively detects the level of DC bias. Upon reaching its maximum value, the FuzzyEn of the vibration signal signifies the core's entry into the saturation zone. Specifically, the maximum FuzzyEn value is approximately 1.5 A on both sides of the core, about 1 A on the left and right sides of the shell, and 2 A in the middle of the shell. These findings confirm the efficacy of the combined CEEMD and FuzzyEn method.

Thermal and insulation performance of the High Voltage Cable Terminal (HVCT) could effectively improve the reliability and economy of power energy transmission. In this paper, a numerical model of the electromagnetic heat flow field was proposed to analyze the heat transfer and temperature characteristics of HVCT under oil leakage defects. This model was the first validated using operation data from the actual equipment and the relative error was less than 1.51%. The effects of oil leakage fault on the global and local temperature distribution of the HVCT were then investigated under different load currents. In addition, the local temperature rise effect of different ambient temperatures on the HVCT oil leakage defect was also considered. Finally, combined with reference indicators such as oil level, temperature, and temperature gradient, a qualitative and quantitative evaluation of the oil leakage fault of HVCT was performed. The results showed that the temperature of the core, surface, and their maximum temperature gradient were linearly related to the ambient temperature. However, the temperature of the core at the oil leak exceeded the normal temperature by up to 7.2 °C with 1000A load current, and the temperature gradient change reaches 681.3 °C/m, which indicated that the convection heat dissipation effect of the oil-deficient part was poor, and the heat accumulates near the cable core. Therefore, the numerical model and analytical results presented in this paper provided an important method for online temperature monitoring and fault analysis of HVCTs.

The icing of overhead high-voltage transmission lines not only caused accidents such as line dance down pole and flashover, but also lead to abnormal field strength on the line surface and distortion of electric field distribution, which threatens the normal operation of the power system. On 500KV transmission lines, a numerical model of the ice cover conductor considering the dielectric properties of the ice layer was established, considering the influence of the spacer strip. The local spatial electric field distribution inside and on the surface of the ice sheet under different ice cover severity was studied. The numerical calculation results showed that the electric field variation inside the ice sheet was amplified, and the electric field distortion rate in the ice cover case was larger than that in the ice-free case at the spacer strip, and both are larger than 150%. In the crescent-shaped transit ice, the aberration rate at the spacer bar inside the crescent-shaped ice decreases with the extension of the crescent-shaped ice, and the electric field aberration rate at the surface of the icicle in the overhanging transit ice was about 20%. The study showed that ice with different characteristics had a significant effect on the electric field around transmission lines, and the study of high-voltage transmission lines over ice could introduce changes in the electric field.

The ocean contains rich and clean renewable blue energy such as wave energy, tidal energy and temperature difference energy. Wave energy, as one of the cleanest renewable energy sources, has the advantages of wide distribution area, long utilization time and huge energy reserves, etc. If the waves in the vast ocean can be used rationally, it can greatly satisfy human energy demand and reduce CO2 emission, and bring profound changes to the world energy pattern and affect all aspects of economy and society. In this paper, we report an Orbital-Train Triboelectric Nanogenerator (OT-TENG) that can collect wave energy in all directions, which consists of a "rail" and a "train". The waves give a push to the train, and the train runs in the track in constant contact with the friction layer on the inside of the track to obtain electrical energy. With a 30° wave push, the OT-TENG can reach a stable voltage output of 100V, a current output of 2.3μA, and a maximum power output of 57.6μW. It can provide electrical power to electronics by charging capacitors. The wave energy on the ocean surface is abundant, and the OT-TENG can operate for a long time to generate electricity. This study shows that the OT-TENG can collect wave energy in all directions, which breaks the directional limitation of existing TENGs and provides a clear direction for the subsequent blue energy harvesting TENGs.

High voltage cable terminals (HVCT) usually work outdoors with water-ingression defect which affects the normal operation of the power system. This paper presents the study of the influence of different water-ingression depth on the temperature distribution of HVCT. Firstly, the model of EM-thermal-fluid coupling field of HVCT was established using finite element method in line with the structural parameters of YJZWC4 HVCT. Subsequently, the effectiveness of the model is verified by comparing the operation of the model under the actual HVCT. Then, the electromagnetic characteristics and temperature characteristics of HVCT are calculated, reacted and detected by the model. The analysis results of temperature show that the surface temperature of HVCT at inlet part is significantly higher than that of the insulating oil part. And the influent depth is positively correlated with surface temperature and temperature gradient. The distortion of the electric field will be more serious due to the deepening of the depth of the inlet water. The research results accurately reflect the electromagnetic thermal characteristics of the HVCT under the influent state. It provides a mathematical fitting expression for the cable terminal model, and provides a technical means for the state prediction and fault diagnosis of cable terminals.

This paper proposes a medium frequency magnetothermal treatment method, which can be used for a certain depth of thermal hyperthermia of tumor tissue in vivo. Firstly, a magnetothermal treatment program using a vortex coil is designed with a medium frequency alternating magnetic field, which can better realize the external implementation. Next, the electromagnetic field of the vortex coil is simulated by finite element method, and the electromagnetic field distribution characteristics of the system are obtained for treatment reference. Then, the preparation and composition design of the gel suitable for the magnetothermal effect are studied, and the temperature rise experiment is carried out to verify the reliability of the temperature rise of the magnetothermal gel. Finally, the human thoracic cavity tissue model is established to calculate the magnetothermal effect of the gel on the lung tumor tissue. And the thermal effect and temperature distribution of different physical parameters on the tissue are obtained. The results show that the magnetothermal therapy can penetrate non-magnetic barriers and effectively generate a temperature rise on the magnetothermal gel injected into the body, so that the tumor tissue in a certain space is inhibited by the temperature rise in a short time. Therefore, the research results in this article provide important theoretical and clinical value for non-invasive hyperthermia of tumors in vivo.

As an important part of livable life, the efficiency and accuracy of landscape data management and scene design of urban footpath have become the new requirements of urban renewal. In this paper, a landscape element segmentation method which can be used in street view images is proposed. This method is based on the PSPnet semantic segmentation model. Firstly, through the cascades of different dimension features, it preserves more details of Street view image on the basis of enhanced scene parsing. And then, a lightweight semantic segmentation model is constructed using the depth separable convolution module to make it more efficient. Finally, through experimental comparison, the average pixel accuracy and average intersection ratio of the proposed method for the sample segmentation of mountain city walk street scene are 82.49% and 77.87%, respectively, which are 10.14% and 13.42% higher than before the improvement. Furthermore, the segmentation results are better than other models commonly used. This method can effectively divide the landscape elements of urban footpaths, which is of great significance for the improvement of urban streetscape data and the promotion of municipal management.

This paper presents an ultra-wideband metal-mountable antenna used in the ultra-high-frequency (UHF) partial discharge (PD) detection. The designed antenna combines a coplanar waveguide antenna and multilayer substrates to effectively broaden its bandwidth when mounted on a conductive surface. These substrates consist of two layers of FR-4 dielectric substrates and two layers of the absorbing gasket, which is adapted to absorb the reflected electromagnetic signals. The parametric study is conducted to optimize antenna performance. A prototype is fabricated to confirm the design, and the measurement results show good agreement with the simulation. When mounted on the metal plate, the proposed antenna covers the UHF bandwidth of 400 MHz–3 GHz for $S_{11} < -10$ dB with a compact size (282 mm $\times242$ mm $\times8.75$ mm). As the thickness of the antenna is only 8.75 mm, the safety distance of electric insulation in electrical equipment will not be affected. A PD experiment has been carried out, and a reference antenna is used in the experiment for comparison. Compared with the conventional antenna, the proposed antenna has a better performance when mounted on the metal plate. It is shown that the designed antenna is a very good candidate for UHF PD detection inside of high-voltage equipment.

In underground cable water tree is the main defect, of which discharge plays an important role in the aging process of insulating materials. To investigate the microscopic mechanism of water-tree discharge in underground cable, a numerical plasma-chemical model is developed. The dynamic characteristics of water-tree discharge are analyzed, including voltage waveform, current waveform, the electron density, electron temperature, ion density, electric field and electron capacitance power deposition. Our results reveal that these waveforms of current and voltage show periodic behaviors. As the increase of the formation of pulse current, the spatiotemporal distributions of electron density and ion density significantly increase, which change the electric field polarity in water tree. Meanwhile the distorted electric field becomes the energy source of electron avalanche and electron temperature. In addition, it was found that capacitive power dissipation gathered on dielectric surface, which aggravates the aging process of the insulation material.

With the development and construction of (high voltage direct current) HVDC system, more and more DC bias problems caused by monopole operation of HVDC are appeared in grid which leads to efficiency droop or potential risk of transformer. This paper proposes a new non-electrical method, Ground-state energy ratio (GER), based on Hilbert-Huangtransform (HHT) characteristics of vibration signals which can reflect the DC bias accurately. Firstly, the transformer DC bias experiment platform is set up and the transformer vibration signals are measured. Meanwhile, the displacement signals are obtained by the quadratic integral. Secondly, the time-frequency spectra of the DC bias vibration signals are obtained by HHT analysis. According to the energy change of each mode in HHT, the GER method is proposed to quantify the DC bias of signal at each point. Lastly, Comparing the GER values of different parts of transformer, such as core, shell and winding, the vibration signals that can accurately reflect the degree of DC bias are confirmed. Results show that the HHT-GER values of vibration signals which on axial vibration of the iron core column and at the top of the transformer shell increase with the increase of DC bias. Therefore, the HHT-GER is an effective method to analyze the DC bias condition of transformer and diagnose the abnormal vibration of transformer core.

The corrosion diagnosis of grounding grid can locate the corroded branches and provide guidance for the maintenance and repair of the grounding grid. This paper proposed the electrical impedance tomography (EIT) method on the corrosion diagnosis of grounding grid and described how it works. Firstly, the inverse problem model of the electrical impedance tomography on grounding grid is developed. Secondly, in order to weaken the ill-posedness of the inverse problem, a Newton iterative algorithm with Tikhonov regularization is proposed to solve the problem. Then, due to the high resistivity contrast between the soli and steel and the large size of imaging region, this paper presents the method of soil-separation and block-diagnosis to accomplish these problems. Finally, field experiments were carried out to verify the effectiveness of the proposed method and the results show that the location and degree of the corrosion in the grounding grid can be easily judged from the imaging results.

Transformer is an important equipment for power energy transmission. The vibration and noise of transformer have always been a serious issue of people concern. Transformer body vibration and noise are mainly caused by the global magnetization of limbs and yokes and magnetic forces of transformer core. However, the process of vibration transfer from core to body is a key factor for monitoring the transformer condition. In this paper, a transformer model for vibration transmission is presented based on motion transmission and it can be used to analyze the vibration relation between core and shell of transformer. Considering strain of silicon steel as the vibration source, the motion equations whichexpress the relations of transformer core and shell are derived. And then, the test system is built to analyze the vibrations of a 5 kVA three phase transformer. A 3D real model simulation used COMSOL finite element software is performed for analyzing the deformation characteristic of transformer. The locations of test points which reflect the vibration more efficiently are determined through the deformation simulation results. Lastly, the vibration signals of two directions have been measured considering DC magnetic bias or not. The experimental results reveal that vibration relations between core and shell are satisfied with the theoretical derivation. Therefore, the Vibration Transmission is significant and it can provide valid method for the DC magnetic bias analysis and core diagnosis of transformer.

Ultra-high frequency (UHF) electromagnetic (EM) signals generated by the partial discharge (PD) process of high-voltage equipment are now widely used in PD detection. The computation of EM propagation generated by a local discharge source using a uniformly hardwiring source can hardly reveal the discharge characteristics. In this paper, a method of near-field to far-field transformation is proposed to realize the study of the propagation characteristics of the PD signal. A short gap discharge model is established to get the near-field electromagnetics and the proposed method is validated by comparing the directly calculated results with the results of the near-field source. In the end, a model of switchgear is employed to study the propagation characteristics of the EM signal based on the proposed method. Via numerical calculation, the influence of the equipment in the switchgear on the propagation of the discharge EM is studied. It is found that the direction of the discharge source has a significant effect on the distribution of the electric field, which indicates that the discharge source cannot be simplified to a uniformly hardwiring source. In addition, it is also obtained that the amplitude of the electric field shows the same trend with the growth of the discharge channel, which gives a method for evaluating the development of the PD. Particularly, the near-field to far-field transformation can provide an effective method for studying the propagation of discharge EM waves in large-scale equipment.

In order to detect the current flowing through concealed conductor, this paper proposes a new method based on derivative method. Firstly, this paper analyzes the main peak characteristic of the derivative function of magnetic field generated by a current-carrying conductor, and a relationship between the current flowing through the conductor and the main peak of the derivative function is obtained and applied to calculate the current. Then, the method is applied to detect the conductor current flowing through grounding grids of substations. Finally, the numerical experimental and field experiment verified the feasibility and accuracy of the method, and the computing results show that the method can effectively measure the conductor current of grounding grids with low error, and the error is within 5 %.

In this paper, a novel resistance network node potential measurement technique based on 16-channel cycle method is presented, and a grounding grids corrosion diagnosis measurement system with 16 channels is built from this method. Through this measurement system, 1680 valid potential data and 1560 effective branch voltage data can be collected in one measurement by only 16 risers on the grounding grid. The stability error of the excitation current source is less than 0.15%, and the error of the applicable acquisition data is about 1% according to system data tests. Built on the measurements, an underdetermined sensitivity equation for solving the increasing multiple of branch resistance is put in place to determine the corrosion status of grounding grids. The experimental results show that the plenty of data is necessary when solving the underdetermined equation and also show that the system is under a high stability, high accuracy, and can comply with the requirements of corrosion diagnosis for grounding grids.

The topology of grounding grid is important for diagnosing its status, which plays a critical role in the safety of personnel and stable operation of power system. The electromagnetic field method and derivative of surface magnetic flux density on the line has been used to measure the branch position in case the grid is parallel to the plane of earth surface that in practice is unknown while the node points and connections were not discussed. This paper introduces a method that uses derivative of surface flux density on circles and lines in a systematic order to find the position of the grid in the plane of the earth surface and connecting the nodes to measure the full topology. This method even identifies any angled branch present in the mesh of a grid. Software simulations and experimental tests verify that the method is feasible and can be applied to identify the topology of a grounding grid.

The laminated joint model is proposed to solve the losses and hot-spot temperature problems of a transformer core, which are mainly caused by the abnormal magnetic field of joints in the laminated core. The different structures and sizes of the joints are considered when designing the proposed model. An equivalent method of joint building factor (JBF) is presented to compute and clearly reflect the relation between losses and structures. Next, a 3D model of transformer for electromagnetic-thermal coupling is designed, and the heat sources of joints and temperature distribution are calculated by using the equivalent iteration of the JBF. Results show that the heat losses and hot-spot temperature of the joints are higher than those of other regions and increase rapidly with the increasing magnetic flux. Finally, a test system using an infrared thermometer is proposed to analyze the hot-spot temperature of joints and clamps. Results indicate that the hot-spots on the joints have the most abnormal temperatures because of the laminated layers. Furthermore, a relative error of less than 2.59% indicates that the theoretical value agrees well with practical values. Therefore, the validity of this calculating method is demonstrated, along with its significance for monitoring temperature and designing transformers. (C) 2016 Elsevier Ltd. All rights reserved.

Monopole operation model of Ultra High Voltage Direct Current (UHVDC) system, DC bias has great influence on the safety and stability of the system, especially for transformers, including temperature rising and increased in vibration. However, there is less research have done on increased vibration of transformer due to influence of DC bias on HVDC system. This study explored transformer vibration caused by DC bias, including the principle of transformer DC magnetic bias and the related calculation method. The mathematical model of the electromagnetic force coupling of the transformer core was also studied and after that its core magnetic field and force field were analyzed. The displacement change of the transformer core which included core clamps and fixed structures were analyzed and discussed. Results revealed that the leakage flux of the clamps increases with DC bias and odd harmonics appeared in each displacement component. Specifically, the direction of the y displacement component changed, and the maximum displacement occurred with the 90-degree phase shift. Then, vibration experiment was done to analyze the DC bias characteristic of core, which also valid the effectiveness of the built simulation mode. Results indicate that amplitude and harmonics of the core limb vibration increase greatly under DC bias condition. The research of paper will also serve as references for addressing the vibration problems of transformers under DC bias conditions.

This paper presents the modeling and simulation of a new rectangular ferrite-loaded waveguide based on left-handed metamaterial (LHM) unit cells at K-u-band. The structure has an 8x8 unit cell configuration, whose negative permittivity and negative permeability are achieved by metallic wires array and ferrite medium, respectively. The equivalent circuit model and transmission parameter matrix for the unit cell are presented based on microwave two-port network theory. The operating frequency is in the TE10 single mode range at 12.97-15.90 GHz where magnetic and electric resonances are coupled simultaneously. The finite-element method (FEM) based simulation software HFSS has been used to set original model and optimized model with vacuum layers for decoupling. Analysis of 3D electromagnetic waves propagation and scattering parameters demonstrate the backward wave property of the optimized waveguide. Negative propagation constant and negative index of refraction are calculated based on a method for extracting effective parameters of LHM. The proposed structure has scalability, double negative, and broad-band operation characteristics in the electromagnetic paradigm.