Under the action of extreme wind load, the overhead transmission line will generate a wind deflection flashover phenomenon, which seriously affects the normal operation of the transmission system and causes significant losses. Y‐type insulator string (hereinafter referred to as Y‐string) is an optimized structural form to reduce the wind deflection flashover in windy areas, and the dynamic mechanical characteristics of Y‐string under the action of pulsating wind is an important factor that influences the design of the overhead transmission line. The calculation method of pulsating wind load and the static calculation method of wind deflection displacement of Y‐string are obtained through theoretical derivation. The mathematical software is used to simulate the time course of pulsating wind speed and convert it into the time course of wind load, establish the finite element model of insulator string, simulate and analyze the wind deflection process of Y‐string under the action of pulsating wind by using the finite element method, and calculate the horizontal displacement of Y‐string under the excitation of pulsating wind and make a comparative analysis with the results of the static calculations. The results show that the wind deflection displacement of the Y‐string under pulsating wind is 1.12–1.28 times that under steady‐state wind, which reveals the reason for the wind deflection flashover phenomenon and provides theoretical references for the design and improvement of overhead transmission lines.

Transmission tower connection joint is an important connection component of the tower leg member and diagonal member. Its axial stiffness directly affects the stable bearing capacity of a transmission tower. The axial stiffness of the joint is mainly related to the connection form of joint. This paper takes the double-limb double-plate connection joint as the research object. Through the comparative study with the single-limb single-plate connection joint, the influence law of single-limb single-plate and double-limb double-plate joint on stable bearing capacity of quadrilateral transmission tower is studied from three aspects of model test, theoretical analysis and numerical simulation. Through the scale model test, it is found that the elastic stiffness of the double-limb double-plate joint is 3.12 times that of the single-limb single-plate joint, which can increase the bearing capacity of the joint by 26.1%. Through the energy method, the theoretical calculation expression of the stable bearing capacity of the quadrilateral tower considering the influence of the axial stiffness of the joint is derived. Compared with the effect of the single-limb single-plate connection joint, the double-limb double-plate joint can improve the stable bearing capacity of the quadrilateral tower by 15.6%. Considering the influence of geometric nonlinearity of tower and connecting joint, it is found that the double-limb double-plate connecting joint can improve the nonlinear stability bearing capacity of a transmission tower by 14.9%. The results show that the double-limb double-plate connection joint can not only improve the bearing capacity of the joint, but also greatly improve the stable bearing capacity of the tower. The research results can provide reference for the engineering application and design of double-limb double-plate connection joints.

The axial stiffness of the connection joints in a transmission tower will affect the stability bearing capacity of the tower. The axial stiffness of different forms of connection joints has different effects on the stability bearing capacities of triangular and quadrilateral lattice towers. This paper takes triangular and quadrilateral lattice towers as the comparative research objects and considers the influence of the stiffness of the single-limb, single-plate joint (SLSPJ) and double-limb, double-plate joint (DLDPJ) of the tower. Under vertical load, the vertical stability bearing capacities of triangular and quadrilateral transmission towers are studied from hte three aspects of theoretical analysis, numerical simulation and test result analysis. The influence rules of the SLSPJ and DLDPJ on the vertical stability bearing capacities of triangular and quadrilateral transmission towers are clarified. Through the energy method, considering the influence of the axial stiffness of connection joints, the calculation expressions of the vertical stability bearing capacities of triangular and quadrilateral lattice towers are derived. Through quantitative analysis, it is found that the axial stiffness of the connection joints has a more significant influence on the vertical stability bearing capacities of triangular lattice towers. The finite element models of the triangular and quadrilateral lattice towers including the SLSPJ and DLDPJ are further established. Through nonlinear finite element analysis, it is found that the DLDPJ can improve the vertical stability bearing capacity of the triangular lattice tower by 22.7% and the quadrilateral lattice tower by 14.9%. Through theoretical calculation, the expressions of the vertical stability bearing capacities of the triangular and quadrilateral lattice towers including the SLSPJ and DLDPJ are obtained. Combined with the test results of the SLSPJ and DLDPJ, it is found that the DLDPJ can improve the vertical stability bearing capacity of the triangular lattice tower by 23.4% and the quadrilateral lattice tower by 15.6%. The research results show that the DLDPJ can improve the vertical stability bearing capacities of triangular and quadrilateral lattice towers. The improvement effect of the vertical stability bearing capacity of the triangular lattice tower is 1.50∼1.52 times that of the quadrilateral lattice tower. The research results can provide a reference for the engineering popularization, application, and design of the DLDPJ in transmission towers.

In this paper, the elastic constitutive relation of polycrystals contains the effect of the mesostucture coefficients. We consider a general case and derive the average elastic constitutive relation pertaining to polycrystals of cubic crystals with any symmetry of crystalline orientation in their statistical distribution. Following Budiansky and Wu, we used self-consistent estimates of eigenstrain to obtain the effective elastic constitutive relation of polycrystals in an explicit form. For the Voigt assumption and the Reuss assumption, the effective elastic constitutive relation of polycrystals on cubic crystals contains the the mesostructure coefficients up to linear terms. In general, the linear term expression works well for materials such as aluminum, the single crystal of which has weak anisotropy. However the same expression (which allows the anisotropic part of the effective elastic constitutive relation to depend only linearly on the mesostructure coefficients) does not suffice for materials such as copper, in which the single crystal is strongly anisotropic. Per the Taylor theorem, we expand the expression based on the self-consistent estimates with respect to the mesostructure coefficients up to quadratic terms for anisotropic polycrystals of cubic crystals. While our numerical data are very close to those of Morris, our expression is much simpler.

Under the action of extreme wind load, the overhead transmission line will lead to the fracture of the traditional V‐type insulator string, which greatly affects the safety of the power system. Compared with the V‐type insulator string, the Y‐type insulator string has better stability under the wind load. Therefore, the overhead lines in the mountainous areas of Anhui Province are taken as the research object, considering the combined effect of wind load and conductor dead weight, and through theoretical derivation, the calculation formula of insulator string wind deflection angle is obtained. Using numerical simulation software, the nonlinear mechanical analysis of Y‐type insulator strings is conducted, and under the action of different wind speeds, the windage yaw angle and unloading angle of the Y‐type insulator string are obtained. Compared with the calculation results of the V‐type insulator string, the stability of the Y‐type insulator string in the structure is better than that of the V‐type insulator string, and the Y‐type insulator string can make full use of the distance between layers and the gap margin of the tower head, reduce the length of the cross arm, and reduce the weight of the tower, which has obvious advantages. Combined with the results of theoretical analysis and numerical simulation, the optimal design method of the Y‐type insulator string is given. Under the condition of ensuring the safety and stability of insulators, the distance of the cross arm is shortened as much as possible and the weight of the transmission line tower is reduced. The research results will provide a theoretical reference for engineering design and improvement.