Existing calculations of leakage energy in the Litz wire winding region of high-frequency transformers usually ignore the influence of Litz wire stranded structures. Therefore, a new approach is established in this paper to accurately calculate Litz wire leakage energy through the segmented equivalent circuit approach and the two-dimensional finite element method. That is, a single Litz wire in a complete stranded pitch is segmented and equated to the linear structure of multiple inductance cells. First, the two-dimensional finite element method calculates the impedance of each strand of Litz wire. Then the strand current vector is solved according to the system equation. Finally, the current vector is substituted back into the 2D Litz wire transverse-sectional model to calculate the leakage magnetic field energy under the skin effect and internal proximity effect, which is combined with the analytical expression of the external leakage magnetic field to calculate the total magnetic leakage energy of the Litz wire winding. Calculation results indicate that the new approach has an average relative deviation of less than 2.154% and a maximum relative deviation of no more than 4.953%.

With the rapid development of power electronics technology, power equipment is moving towards high power density and miniaturization. Therefore, in order to solve the problems of large volume and high losses in traditional transformers, the application of power electronics technology to power transformers and the research and development of high-frequency transformers have become a hot direction in the power industry. This article constructs a 10kHz/50kW four-winding transformer with nanocrystalline core and litz wire winding. Accurately calculated the electromagnetic loss characteristics of high-frequency transformers under no-load test. And through electromagnetic temperature field coupling calculation method, Calculate the temperature distribution of high-frequency transformer under natural convection. Then analyze the hot spot temperature.

To ensure unmanned aerial vehicles (UAVs) complete the inspection task of a high-voltage transmission line safely and effectively, it is necessary to consider the interference of a complicated electromagnetic field near a high-voltage transmission line and determine a reasonable inspection distance and path of the UAV. Taking the 500kV EHV AC power line as an instance, firstly, the three-dimensional model of the 500kV ZV 1 cup-tower is built, and the finite element method (FEM) is used for computing the electric field and magnetic field of the UAV exterior. According to inspection specifications, the electromagnetic field protection threshold of the UAV is determined, and then the safety area between UAV and the split conductor is determined to be equal to 1.5 m. Combined with the UAV shooting field of view and safety distance, the spatial positions of UAV hovering shooting points are selected to ensure that UAV flies in a safe area. Finally, the path of UAV traversing hovering shooting points is optimized by the ant colony algorithm (ACO), and the optimal path distance is 109.4 m.

This paper mainly aims at the problems existing in the safety maintenance of overhead transmission lines, including the poor stability and low adaptability caused by the insufficient locking adaptability of the dwell device to different sizes of ground wires. In addition, during live working on transmission lines, there is also a lack of safety awareness among operators. The problems with these safety violations include not wearing helmets, safety belts and safety harnesses. To this end, this paper proposes a design of an overhead transmission line safety violation identification and stationing device based on a stationing drone and YOLOv5 algorithm. The scheme aims to improve the efficiency and accuracy of safety maintenance, and provide a strong guarantee for the safe operation of overhead transmission lines. Firstly, this paper designs the dwell device to improve its locking adaptability to different sizes of ground wires. After that, collect the image and video data of overhead transmission lines, and then annotate them for data preprocessing and preparation. Finally, the safety helmet, safety belt, safety harnesses and red vest detection model based on YOLOv5 algorithm is used to identify whether the operators are wearing safety helmet, safety belt and safety rope, and whether there are personnel wearing red vest at the work site. Furthermore, a safety violation behavior recognition algorithm framework based on human key point detection and attention mechanism has been proposed to effectively identify four types of safety violations, including not wearing a helmet, not wearing a seat belt, not tying a safety rope, and whether wearing a red vest. The experimental results show that the YOLOv5 algorithm based safety violation behavior recognition model has high accuracy and recall rate, effectively identifying safety violations in overhead transmission lines. This study provides a new intelligent solution for the safe maintenance of overhead transmission lines, which has certain practical application value.

Using a single heuristic algorithm to optimize the trajectory of a UAV (unmanned aerial vehicle) patrol inspection transmission tower body and accessories will result in trajectories overlapping and easily falling into the local optimal solution. As a result, this paper presents a hybrid GA (genetic algorithm)-SA (simulated annealing algorithm) optimization algorithm for UAV 3D trajectory. To optimize the trajectory of the UAV traversing the safe hovering point at high altitude, GA, SA, and hybrid GA-SA algorithms are used on the 500 kV UHV AC double-loop drum tower of UAV patrol inspection. The results show that the hybrid GA-SA algorithm has the shortest optimal trajectory distance and the shortest iterative convergence times, proving the effectiveness of the proposed method.

Cold-formed steel triple-limbs built-up columns with half open sections, which are generally used in shear wall chords, corner column of exterior walls, door and window opening frame jambs, and other parts that need to be strengthened, are becoming increasingly popular. At present, no systematic research is available for such section type. Therefore, this paper reports on a comprehensive experimental investigation addressing the buckling behavior of triple-limbs built-up columns affected by pure global, distortional, and local buckling modes. In total, the results from 54 experimental tests are reported. Different screw spacings were designed for each specimen with the same cross-sectional dimension and length in order to study its effect. In addition, the isolated shear performance of the screws used in the built-up columns was investigated through single shear screwed connection tests. It was observed that the G type, D type, and L type triple-limbs built-up columns were failed by pure global, distortional, and local buckling, respectively, and the longitudinal spacing of the screws did not seem to significantly affect the occurrence of the failure mechanism, but can affect the ultimate strength of the specimen. Finally, the ultimate strengths obtained in the test were compared against the predicted strengths calculated in accordance with the current direct strength method, which is provided in AS/NZS 4600 (2018) and AISI S100 (2016). The comparisons show that the direct strength method is accurate and reliable for the design calculation of pure buckling mode of triple-limbs built-up columns.

Medium-frequency transformer (MFT) is the core component of high voltage and large capacity DC/DC converter, but high frequency and high power density will lead to intensified transformer vibration. Magnetostriction and air gap Maxwell force are the main sources of vibration and noise. In this paper, nanocrystalline alloy with high saturation magnetic density, high magnetic permeability and low high frequency loss is used as the core of MFT to study its vibration characteristics. Considering the influence of transverse isotropy of nanocrystalline alloy core mechanical properties, the transient electromagnetic field-structure field weak coupling calculation method based on ANSYS finite element method is used to calculate two MFTs with 10kVA/5kHz shell-type and core-type nanocrystalline cores under no-load sine condition. The calculated volume force is imported into the structural field to obtain the vibration acceleration and displacement changes of the core, and the simulation value is compared with the experimental measurement value. The results show that the vibration of the shell-type core is stronger than that of the core-type core under the action of Maxwell force and magnetostrictive force. And the vibration acceleration frequency is twice the excitation frequency. The research in this paper can provide a basis for the design and optimization of vibration and noise of MFT.

Long-distance, large-capacity UHV transmission lines have increasingly become a key part of the construction of my country’s UHV power grid. However, with the increase of voltage levels, the electromagnetic interference of UHV transmission line towers to neighboring radio stations has become more and more serious, resulting in It is inevitable to study the secondary radiation suppression method of UHV transmission line towers. Therefore, based on the mechanism of suppressing the maximum value of secondary radiation, this paper proposes a secondary radiation suppression method for UHV trans- mission line towers in the mid-wave frequency band, and develops a secondary radiation suppression device based on the principle of this method. The final result shows that when the secondary radiation suppression device is not installed, the electromagnetic interference received by the measurement point is 0.4dB; after the secondary radiation suppression device is installed, the electromagnetic interference received by the measure-ment point is reduced to 0.1dB.

共享铁塔将电力和通信设备集成一体,其新增的基站天线与铁塔上原有的输电线路在线监测设备近距离架设,不可避免地会对在线监测设备产生电磁干扰.根据现有在线监测设备的电磁兼容标准,分析了基站天线对在线监测设备的干扰机理,建议以射频辐射抗扰度10 V/m为抗干扰设计限值.结合天线原理,推导了基站天线场源的数学表征式,进而提出了多基站天线辐射下,电大尺寸金属散射体在空间任一点处散射场求解的数学模型.采用PO-MoM混合算法对提出的数学模型进行求解,并通过电波暗室实验对其进行验证,结果表明,数学模型的全局最大相对偏差值随频率的增加而增大,在2 600 MHz时为8.33％.以山东共享铁塔为算例,分析了铁塔塔头型式、天线功率、天线倾角3种工况下在线监测设备处电场强度变化规律,并以此为依据,建议将天线与在线监测设备之间的防护间距定为4 m.

500 kV猫头塔在中国超高压输电网系统中发挥着重要的作用,但其在覆冰舞动条件下的倒塌事故频繁发生.针对覆冰舞动条件下输电铁塔杆件内力的准确计算问题,首先引入超静定结构的概念,提出了一种基于n次超静定结构的杆塔内力求解方法;然后根据导地线参数推导出了覆冰舞动条件下挂线点的受力情况;最后基于铁塔桁架结构和载荷分布的对称性,将全塔模型简化为1/4模型进行内力计算,并对螺栓组的连接强度进行校验.以500 kV宜兴Ⅰ回线路141#为例,对新方法的计算准确性进行验证.结果表明:内力计算值与仿真值之间的偏差均小于10％;采用新方法能够实现薄弱点的准确定位,并对薄弱点周围的螺栓组采取补强措施.研究结果对今后的舞动区铁塔设计和改造具有一定的指导意义.

随着共享铁塔建设的全面开展,基站天线对同塔布置的输电线路在线监测设备的电磁干扰问题开始凸显.结合在线监测设备的电磁兼容标准,揭示了基站天线对在线监测设备的电磁干扰机理.通过建立电大尺寸金属散射体无源干扰求解模型,采用物理光学-矩量法混合算法求解基站天线在铁塔表面产生的感应电流,获得了在线监测设备处的散射电场值.以山东35 kV共享铁塔为算例,以天线工作频率、天线与在线监测设备之间的间距为变量,分析了铁塔塔头型式、天线功率、天线倾角等不同工况下的散射电场变化规律.结果 表明,铁塔塔头型式对干扰影响较小,而天线功率和倾角对干扰影响较大.以此为计算依据,建议天线与在线监测设备之间的防护间距为18 m.

为得到航空无线电导航台站的防护间距,建立基站天线激励条件下的共享铁塔电磁散射求解模型,采用矩量法和物理光学法对电场积分进行混合求解,并针对兆赫兹频段带来的阻抗矩阵求解资源量过大的问题,提出引用多层快速多极子算法(multi level fast multipole method,MLFMM)以降低计算复杂度,实现测距台站处的干扰场强求解.以共享铁塔的安装方式、铁塔塔型、铁塔基数为变量,分别求解了3种因子条件下干扰场强的变化规律,并以干扰防护率为阈值,建议航空无线电导航台站信号覆盖范围内的共享铁塔与航空无线电导航台站测距信标台之间的防护间距为11.1 km.

IEEE对中波频段输电线路无源干扰谐振机理及其影响因子进行了较为深入的研究,但相关结论无法解释短波频段无源干扰仍存在的谐振现象.为得到短波频段输电线路无源干扰谐振的决定性影响因子,考虑各种可能对干扰造成影响的因素,如线路档距、铁塔数量、导线、地线等单一宏观结构,研究输电线路与天线组成的电磁开放系统中场域的无源干扰水平.引入灰色系统理论及相关性分析,计算各种影响因子对干扰变化的灵敏度,得到各种宏观结构与干扰的关联程度.分析结果表明,线路档距是短波频段无源干扰谐振的决定性影响因子,线路设计阶段可采取调整档距的方法规避干扰极值频点.

Audible noise prediction is a hot research area in power transmission engineering in recent years, especially come down to AC transmission lines. The conventional prediction models at present have got some problems such as big errors. In this paper, a prediction model is established based on BP network, in which the input variables are the four factors in the international common expression of power line audible noise and the noise value is the output. Take multiple measured power lines as an example, a train is made by the BP network and then the prediction model is set up in the hidden layer of the network. Using the trained model, the audible noise values are predicted. The final results show that the average absolute error in absolute terms of the values by the audible noise prediction model based on BP neural network is 1.6414 less than that predicted by the GE formula.

The progression of power transformer core is usually determined by the core diameter and the width and thickness of the silicon-steel sheet is determined by the graphing method. Therefore, coil section can’t be fully utilized. To analyze the manufacturing characteristics of power transformer core columns from the performance and material savings and the nonlinear integer regression programming model is established. Taking the circumscribed circle diameter is 800mm, progression equal to 17 as an example. The optimized design of column section is solved by using the MATLAB. The results show that the optimized design can increase the cross-section fill factor by 3.8% and the diameter of the core columns larger, the optimization results better.

Reducing tower ground’s impulse grounding resistance can prevent the power lines from lightning effectively. The concept of impulse grounding resistance is described. Calculation formula of the impulse grounding resistance for ground electrode in different Conformations is derived with impulse coefficient method. The conformation of the ground electrode is improved according to the theory of impulse grounding resistance is decreased when the effective area of the electrode is reduced, using ETAP for simulation of the improved ground electrode. The results show that the impulse grounding resistance of the improved ground electrode can be reduced to 41.1% of the original, and safety margin is larger in practical engineering.

The accurate algorithm, which is used in the calculation of tower grounding resistance of power line in vertical layered soil, is difficult for normal engineering personnel to handle. Based on Green function, the resistance of typical tower grounding device is calculated. Therefore, the fitting function, which represents the relationship between resistivity of vertical layered soil and resistance values of grounding device, is deduced with the hyperbolic function as a fitting function using the least squares curve fitting methods. At last, the fitting formula of tower grounding resistance with the vertical layered soil model is acquired. According to the precision analysis, it is found that the accuracy of proposed formula is related with the initial value, but its maximum error does not exceed 10%.

In the construction of UHVDC power line in China, the national standard of reradiation interference protecting distance between UHVDC power line and receiving station of AM broadcasting needs to be renewed. In this paper, the wire-surface simulation model is used to calculate the interference. In the model, steel tower is represented as surface model, ground wire is represented as wire model, and the whole model is excitated by vertical polarization plane wave. For the deficiency of traditional solution method of protecting distance calculation, a new method is proposed. It is recommended that the whole work frequency band of receiving station should be calculated to determine the space interval which has actual protecting distance. Then the interval is gradually narrowed with dichotomy method until the interval size is within allowable value. With the first-grade receiving station of AM broadcasting as example, the reradiation interference protecting distance from UHVDC power line and station is calculated.

There is the resonance phenomenon in the reradiation interference on wireless station from power lines. The wire-surface simulation model, in which steel tower is represented as surface model and ground wire is represented as wire model, is excitated by vertical polarization plane wave. Based on the method of moments (MoM), the base function of wire-surface model junction point and the computation method are discussed. With various frequencies, the interference values are calculated. The possible impact factors of interference resonance, such as ground wire, conductor, number of towers and tower spans, are studied. The results show that the decisive impact factor on reradiation interference is tower spans. It is concluded that interference is mainly decided by electromagnetic scatter from power towers in short wave and above.