Iced Transmission Lines Research Articles

Two Simplified Methods for Galloping of Iced Transmission Lines

For the galloping of iced transmission lines, the influences of two simplified methods of dynamic tension on the galloping characteristics of transmission lines are investigated. Based on the variational principle for Hamiltonian, the partial differential equation of galloping of iced transmission lines is derived, then it is transformed into ordinary differential equation by Galerkin method. Two different simplified methods are used to convert the partial differential equation into ordinary differential equation. One is to average the dynamic tension over the span length, then Galerkin method is used. The other is that Galerkin method is used to convert the partial differential equation into ordinary differential equation directly. Firstly, the influences of two simplified methods on coefficients of ordinary differential galloping equation are studied. Second, the influences of the bending stiffness on the first-order frequency have been researched. In addition, the average method of two degrees of freedom (DOFs) is proposed and the galloping characteristics of iced transmission lines are studied by using multiscale method and average method, then the results are compared with that obtained by using numerical method. The parameters analysis shows that the two simplified methods of dynamic tension have significant influences on the coefficients of the two DOFs ordinary differential equation. By comparing the coefficients of galloping equation obtained by the two simplified methods of dynamic tension, it can find that with the increasing of tension and span length, the influences of bending stiffness on in-plane and out-of-plane natural frequency becomes smaller and smaller. The results of multiscale method and average method both show that the two simplified methods of dynamic tension have certain influences on the frequency, phase and amplitude of galloping of iced transmission lines. The conclusions obtained by this paper would promote the perfection of theoretical modeling about iced transmission lines, and could also give some references to practical engineering.

Galloping Suppression of Iced Transmission Lines by Viscoelastic-Damping Interphase Spacers

AbstractGalloping of iced conductors is a kind of self-excited aeroelastic vibration at low frequency and large amplitude causing various damage to transmission tower-line systems. This paper propo...

Galloping Stability and Aerodynamic Characteristic of Iced Transmission Line Based on 3-DOF

A new calculation method of critical wind speed based on three degrees of freedom (3-DOF) is proposed for galloping problem of iced transmission line. Based on the quasistatic theory, the aerodynamic load of iced transmission line is obtained, which considers the influence of transverse and torsional motion on the relative wind angle of attack. Finally, the equivalent galloping model of 3-DOF iced transmission line is established. At the initial angle of attack, the aerodynamic load is expanded by Taylor, and the unsymmetrical linear aerodynamic coefficient matrix is obtained. The Routh–Hurwitz criterion is used to judge the stability of iced transmission line system, and then the critical wind speed is calculated. The in-plane and out-plane frequencies corresponding to the first-order mode of the transmission line are solved by the analytical method and numerical simulation method. The results obtained by the two methods are compared and verified. The influence of dimensionless transmission line parameterλon the in-plane and out-of-plane frequencies is discussed. The aerodynamic coefficients of the iced transmission line are measured by wind tunnel test and the aerodynamic characteristics are analyzed. According to the theoretical formula, the critical wind speed is calculated by MATLAB. The critical wind speed determined in this paper is compared with the critical wind speed determined by Den Hartog and Nigol theory. The influences of torsional vibration frequency, ice thickness, and ice shape on critical wind speed are analyzed. The research results of this paper have important theoretical significance for the stability judgment of iced transmission lines.

Prediction method for galloping features of transmission lines based on FEM and machine learning

Parameter study on galloping of iced transmission lines with different structural, ice and wind parameters is carried out by means of the finite element method (FEM), and a dataset is then created based on the numerical results. The random forests algorithm is used to set up a classification model to predict the galloping mode and vertical vibration mode. Using the span length, initial conductor tension, ice thickness, initial wind attack angle, wind velocity and the galloping mode as well as the vertical vibration mode obtained by the classification model as the input variables, a back-propagation (BP) neural network model is created to predict the galloping features including the frequencies, vibration amplitudes and the maximum conductor tension. The dataset created based on the parameter study is divided into two sub-datasets for training and testing of the two machine learning models respectively. The effects of the input variables on the output variables are quantified with a feature importance analysis for the classification model and a global sensitivity analysis for the feature prediction model respectively. The two models are finally integrated into one to predict galloping features efficiently and quickly. Making use of the proposed method, an early warning system for galloping of transmission lines may be able to be set up in the future.

LIMIT CYCLE BIFURCATIONS IN THE IN-PLANE GALLOPING OF ICED TRANSMISSION LINE*

In this paper, we establish a mathematical model to describe in-plane galloping of iced transmission line with geometrical and aerodynamical nonlinearities using Hamilton principle. After Galerkin Discretization, we get a two-dimensional ordinary differential equations system, further, a near Hamiltonian system is obtained by rescaling. By calculating the coefficients of the first order Melnikov function or the Abelian integral of the near-Hamiltonian system, the number of limit cycles and their locations are obtained. We demonstrate that this model can have at least 3 limit cycles in some wind velocity. Moreover, some numerical simulations are conducted to verify the theoretical results.

Numerical simulation of unsteady galloping of two-dimensional iced transmission line with comparison to conventional quasi-steady analysis

Most of the previous works on numerical analysis of galloping of transmission lines are generally based on the quasi-steady theory. However, some wind tunnel tests of the rectangular section or hangers of suspension bridges have shown that the galloping phenomenon has a strong unsteady characteristic and the test results are quite different from the quasi-steady calculation results. Therefore, it is necessary to check the applicability of the quasi-static theory in galloping analysis of the ice-covered transmission line. Although some limited unsteady simulation researches have been conducted on the variation of parameters such as aerodynamic damping, aerodynamic coefficients with wind speed or wind attack angle, there is a need to investigate the numerical simulation of unsteady galloping of two-dimensional iced transmission line with comparison to wind tunnel test results. In this paper, it is proposed to conduct a two dimensional (2-D) unsteady numerical analysis of ice-covered transmission line galloping. First, wind tunnel tests of a typical crescent-shapes iced conductor are conducted firstly to check the subsequent quasi-steady and unsteady numerical analysis results. Then, a numerical simulation model consistent with the aeroelastic model in the wind tunnel test is established. The weak coupling methodology is used to consider the fluid-structure interaction in investigating a two-dimension numerical simulation of unsteady galloping of the iced conductor. First, the flow field is simulated to obtain the pressure and velocity distribution of the flow field. The fluid action on the iced conduct at the coupling interface is treated as an external load to the conductor. Then, the movement of the conduct is analyzed separately. The software ANSYS FLUENT is employed and redeveloped to numerically analyze the model responses based on fluid-structure interaction theory. The numerical simulation results of unsteady galloping of the iced conduct are compared with the measured responses of wind tunnel tests and the numerical results by the conventional quasi-steady theory, respectively.

PR-KELM: Icing level prediction for transmission lines in smart grid

As a hot spot, the diffusion of the smart city has been more and more popular and widespread all over the world. The concept of smart city has supported a higher quality of urban spaces and a better offering of public services. Smart grid is an important component and the energy supply of smart city. The health of the smart grid will directly affect the health of the smart city. Efficient and accurate prediction about icing level of transmission lines provides a reliable basis for anti-icing and deicing of power grids. The prediction can not only significantly enhance the reliability, safety and stability of transmission networks, but also timely provide the state monitoring of ice on wires to the workers to make proper decisions and to prevent freezing disasters so as to effectively protect people’s safety and build a stable and friendly society. To reduce catastrophic damages caused by the iced transmission lines of the grid, this paper proposed a novel hybrid model called PR-KELM, an integration of Principal Component Analysis, ReliefF and Kernel based ELM (Extreme Learning Machine) method to predict the icing level of transmission lines. This hybrid model covered two stages including: 1) structured and unstructured data feature extraction by local binary patterns, principal component analysis and ReliefF; 2) radial basis function Kernel based ELM predicting the processed data. The experimental data adopted in this paper were from the online monitoring system of South China State Grid Online Monitoring System by terminal CC0289 between December 1, 2011 and March 1, 2016. Experimental results indicated: compared with Elman neural network model, random forest model, support vector machine model and Bayesian networks model, PR-KELM approach demonstrated high accuracy and lower prediction error in terms of RMSE (Root Mean Square Error), MAE (Mean Absolute Error), MAPE (Mean Absolute Percentage Error), and R (Coefficient of Correlation) while applied to predicting in real datasets.

Thermodynamic model of critical ice-melting current on iced transmission lines

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.

Wind tunnel test of the influence of an interphase spacer on the galloping control of iced eight-bundled conductors

To study the anti-galloping effect of interphase spacers with different kinds of arrangements on an iced transmission line, wind tunnel experiments using a full aeroelastic model are carried out in this work. Using similarity theory, the similarity criteria between the aeroelastic model and the prototype have been deduced. A triangular arrangement of three phases is considered, and the arrangements of iced eight-bundled conductors with and without the spacers are divided into six cases. In the experiments, laser sensors at different positions along the span of each phase are used to measure the variation of dynamic displacements with wind speed. Furthermore, galloping characteristics, such as the responses, frequencies, vibration modes, amplitudes and distance between two phases, are obtained for different wind speeds and arrangements. The obtained results show that interphase spacers have a certain inhibitory effect on the first symmetric mode and the first anti-symmetric mode galloping, but not all of the arrangements have a positive effect. The regularity of the variation with wind speed of the anti-galloping effect with interphase spacers is summarized. The galloping amplitude curves indicate that the amplitude is likely to be larger when a modal transformation occurs, in contrast to the results obtained without interphase spacers. The motion of the phase C located close to the diffusion section is different from those of the other two phases. Moreover, due to interphase spacers, the distance between the two phases is increased. The obtained conclusions can be used to predict the positions of interphase spacers and provide a fundamental tool for anti-galloping of eight-bundled conductors.

Research on the Test of Transmission Line Galloping

The load of iced transmission line and the load generated by galloping after the conductor are covered by ice all may cause severe circuit faults, such as tripping, conductor breaking, armor clamp damage and even tower collapse, thus severely threatening running safety of power system. The generation and development processes of galloping of power transmission line is very complicated, and numerous factors may influence the galloping excitation, such as environmental factors, terrain factors and structural parameters of power transmission line; in which, the ice covering of conductor is one of necessary factors causing galloping. Therefore, researches on ice covering increasing test of different types of conductors under different meteorological conditions have been conducted in large-sized multi-functional phytotron, thus obtaining the relation curve of ice covering increasing of conductor along with time under different conditions, and analyzing factors influencing increasing of ice covering. The research result shows that under the same ice covering conditions, the increasing of ice covering of conductor with small diameter is relatively rapid; both environmental temperature and wind speed have obvious influence on increasing of ice covering of conductor, and the environmental temperature will decide the type of ice covering of conductor surface. Meanwhile, after wind tunnel tests targeting conductors with different ice covering shapes, pneumatic stability loss characteristics of conductors with different ice shapes have been obtained. Research results have important scientific reference value for revealing the mechanism of galloping of iced power transmission line, and have relatively high engineering practicability value for promoting realization of early warning system for galloping of iced power transmission line.

An Improved Algebraic Method for Finding the Jump Height of Iced Transmission Lines

An Improved Algebraic Method for Finding the Jump Height of Iced Transmission Lines

Numerical Simulation Analysis of Asymmetric Fatigue Failure for Iced Electric Power Transmission Line

Accident of icing induced line break occurred for the electric power transmissionline connecting Yucheng to Pugein the winter of 2011. Based on the observation and measured data, a broken section of the LGJ- 630/45- type power line of stranded aluminum wires with steel core exhibited 12 broken aluminum wires with typical brittle fracture characteristics, but the rest wires were ductile fractured.On the basis of the theory of statics and dynamics of catenary beam element mode and large deflection bending beam element mode, the line breaking was analyzed by using ANSYS finite element method. Results show that the brittle fracture of 12 broken wires may be caused by fatigue, then the effective section of power line decreases, which further caused the rest wires to be broken due to overload. Icing and fluctuating wind lead the stress of the operating power line to be increased from 55.4 MPa to 97.9 MPa,which is the main cause to the line breaking. The power line resonate induced by the fluctuating wind,thus the mean stress of asymmetric fatigue increases,, and the fatigue life of the line significant decreases. Corresponding to all the above considerations, the realstress of the operating line increases from97.9 MPa to 275.2 MPa and thereby the ductile fracture occurs due to that the real stress exceeded the failure stress of 221 MPa of the operating line.

A method to calculate the reactive power of iced transmission line based on Poynting vector and FDFD

A method to calculate the reactive power of iced transmission line based on Poynting vector and FDFD

A method to calculate jump height of iced transmission lines after ice-shedding

Based on the energy conservation, stress–sag relation, geometrical relation of spans and dynamic relation of clamps connected with suspension insulators of a multi-span transmission line following ice-shedding, a theoretical method to calculate the maximum jump height of the line is presented. The jump heights of transmission lines with various parameters, including the number of spans, span length, conductor type, ice thickness and suspension insulator length, after ice-shedding are determined by the presented method and the finite element method, and the results obtained by both methods agree well. The method presented in this paper is more accurate than those previously proposed by other authors and more convenient than the finite element method. It is suggested that the presented method be employed to predict the jump height of a transmission line located in an ice zone after ice-shedding, which is a key factor in the design of electric insulation clearance.

Study on the Iced Quad-Bundle Transmission Lines Incorporated With Viscoelastic Antigalloping Devices

The viscoelastic damper is one of the most promising devices for vibration mitigation. In order to reduce dynamic responses of iced transmission lines due to strong wind, a new kind of viscoelastic antigalloping device (VEAGD) is developed. Experimental and theoretical studies indicate that the device has fine energy dissipation capacity and high damping characteristic. Then, the motion equations of the iced quad-bundle transmission lines incorporated with VEAGDs are established by employing Lagrange equation based on the assumed mode method. At the same time, the parameters and positions of the VEAGDs are determined optimally by the genetic algorithm. Numerical analysis results show that VEAGDs have excellent antigalloping effect, and the dynamic responses of the transmission lines with optimally designed VEAGDs are mitigated more effectively.

Nonlinear Vibration and Multimodal Interaction Analysis of Transmission Line with Thin Ice Accretions

A study of multimodal galloping is carried out on an iced transmission line with thin ice accretions. The partial differential governing equations of iced transmission line are established to describe the nonlinear interactions between the in-plane, out-of-plane and torsional vibration, in which geometrical and aerodynamic nonlinearities are considered. The transformation of modal galloping with the continuous variations of parameters and modal interactions are analyzed based on the reduced model obtained by employing Galerkin spatial discretization. Eigenvalue analysis is applied on linear system to determine the switch of different modal galloping in plane U -l, where Hopf bifurcation occurs and mono-modal, bi-modal and multi-modal galloping are observed. Various numerical procedures are implemented to capture the outstanding nonlinear dynamic features of every regional galloping in plane U -l. Internal resonance is observed and investigated to interpret the phenomenon of modal transition which is also analyzed by accounting for the influence of initial conditions on galloping with either symmetric or anti-symmetric modes.

The Aerodynamic Analysis for Iced Four Bundled Transmission Lines with Typical Crescent

Despite the fact that the wind tunnel tests have been carried out on iced transmission lines subjected to wind load, it is not practical to do wind tunnel tests due to its high cost. This paper describes a detailed numerical simulation method that can be used to instead of wind tunnel tests. Based on the galloping mechanism of iced transmission lines, the aerodynamic test was simulated with the typical crescent super-large thickness iced four bundled conductors. One of the results highlighted in this study is that the wind angle of attack had significant influence on the aerodynamics of iced conductors. The Den-Hartog and O.Nigol coefficient were calculated to determine galloping of iced transmission lines, comparing with the reference of wind tunnel test in the Zhejiang university, the range of the wind angle of attack to the bundled conductor which can lead to gallop is larger than single wire, but the absolute value of amplitude is less than the single conductor, split conductor is more likely to gallop than single conductor.

Numerical Analysis of the Iced Transmission Line Galloping

By used the assumed mode method to simulate the iced transmission line galloping,with three generalized coordinates to represent the iced transmission line galloping. In order to avoid the complicated calculation of vector,used the Lagrange equation to build the nonlinear equations of iced transmission line from the perspective of energy,used the Runge-Kutta numerical calculation to solve the equations of motion and get the iced transmission line’s across-wind,along-wind and the torsional response. Based on Lyapunov stability theory to deduce the critical wind speed of the iced transmission line galloping. And had used a test iced transmission line to verify the feasibility of the numerical solution and the critical wind speed.

Analysis of Weak Position in Overhead line under Heavy Icing Condition by Finite Element Method

Transmission tower is an important component of power system, and heavy iced transmission line has became one of the important factors against its safety and stability in China's power system these years but the transmission line designed from traditional standard can't endure the more worse environment. In this paper, for positioning the weak points of the transmission line under heavy icing accurately and providing accurate positional parameters to online monitoring devices, the strain section model is built to analysis their mechanical properties under icing and wind conditions .In proposed method, the coupling effect between tower and lines is considered, then the weak tower is picked out by strain section model that is combined with eight towers. The single one-tower-two-lines model of weak tower is built to simulate and verify the weak point accurately. Finally the better way is defined to get the location of weak structure combined with the advantages of both models.

Investigation into galloping characteristics of iced quad bundle conductors

A nonlinear finite element method for galloping of iced bundle conductor transmission lines is presented. Wind tunnel tests for galloping of quad bundle conductor segments with crescent-shaped and sector-shaped ice models were carried out, and validity of the finite element method is demonstrated by the consistency of the galloping responses determined by the numerical method and those measured by the wind tunnel tests. Numerical models of four sections of iced transmission lines with different Irvine parameter λ2, which determines if internal resonance exists, are set up. Galloping of the iced transmission lines in steady wind flow and stochastic wind field is numerically simulated by the presented finite element method. Based on the numerical results, galloping characteristics of the iced transmission lines with and without internal resonance in steady and stochastic wind fields are discussed. It is found that the galloping mode and frequency of an iced quad bundle conductor transmission line in a stochastic wind field are similar to those in a steady wind flow, but the galloping amplitude may be different. Moreover, the Irvine parameter λ2 may be used to estimate some galloping characteristics, such as galloping mode and coupling movement induced by internal resonance.