Iced Conductor Research Articles

Modal Analysis of the Iced Transmission Line Based on Three-Dimensional Curved Beam Element

The accurate calculation of transmission line modes is very important for power line design, the dynamic properties, anti-vibration, anti-galloping analysis. However, the existing simplified theories and models will Cause large calculation error. Based on the strain - displacement relationship of spatial curved beam theory, a three-node curved beam power line element was realized, which was used to take a modal analysis. The results show that the curved beam element used to calculate modes of power line is accurate. The results of the analysis were compared with results of only considering translation of power line, results of considering axial deformation and bending. The results of parametric analysis show that the bending cross-section modulus of the transmission lines has a greater impact on the translation and rotation frequency. The iced conductor eccentricity can slightly reduce the frequency of wire.

Finite Element Analysis on Dynamic Tension of Quad-Bundle Conductor of Transmission Line Galloping

For profoundly understanding the influence of wind speed on the dynamic tension of iced bundle conductor, the influence of wind speed on galloping rules, tension variation, and amplitude of quad-bundle conductor under number 4-8 wind were investigated by nonlinear finite element analysis and theoretical analysis methods. The results shows that wind speed have great influence on galloping amplitude and dynamic tension. Galloping amplitude will rapidly increase with the increase of the wind speed at the beginning, but when the wind speed increased to a certain extent, the increase of galloping amplitude in plane and dynamic tension will become not obviously, and the maximum dynamic tension approximately doubles the static tension. The galloping and tension variation rules of bundle conductor were changed from stability periodic motion to complicated quasi periodic motion.

Nonlinear Numerical Simulation of Iced Conductor Galloping

A two-node cable element which the axial torsion and geometrical nonlinear were considered was developed based on the update Lagrange formulation, and a model of multi-span transmission line for galloping analysis was established. A nonlinear numerical simulation of single iced conductor galloping was proposed. Using computational fluid dynamic, the aerodynamic coefficient of iced conductor with different wind attack angle was simulated. According to the finite element model of multi-span transmission line and aerodynamic coefficient curve, the galloping of iced conductor through the method of fourth-ordered Runge-Kutta method was presented. By the comparison with the classical examples, the results indicated that the presented method are efficient and reliable.

Study on Numerical Simulation of Iced Conductor Galloping for Multi-Span Power Transmission Lines

The general expression of Lagrange nonlinear cable element is established firstly by using virtual work principle. On the basis of the theory, the specific expression of a two-node cable element having rotational degree of freedom is derived and the non-linear finite element model of multi-span transmission line for galloping analysis was established. In addition, the aerodynamic coefficient of iced conductor under different wind attack angle was obtained through computational fluid dynamics method. Based on the finite element model and aerodynamic characteristics of the iced conductor, the Runge-Kutta method was applied to carried out non-linear numerical simulation of iced conductor galloping and the Matlab program was compiled. The galloping of the multi-span transmission line crossing Hanjiang River was analyzed. The results indicate that the presented method can simulate the galloping process effectively and it can provide the basic references for further research of preventing galloping.

Simulation and Experimental Investigation of DC Ice-Melting Process on an Iced Conductor

Ice melting with dc is one of the key technologies to prevent the Chinese power grid from ice storms. Especially after the severe ice storm in the southern part of China in early 2008, dc ice-melting technology has drawn more attention than ever before. However, there are few satisfactory methods to select correct parameters so the ice-melting project rarely achieves desired effects in some cases when applied in Hunan, Guizhou, and other provinces in China. Therefore, it is of great significance to develop a method to estimate parameters which is applicable in the practical situation for dc ice melting. To handle this, the factors, such as wind velocity, ambient temperature, current density and ice-layer thickness were analyzed and then a dc ice-melting model is put forward in this paper. Both the results of simulations and experiments show that the ice-melting process can be divided into three stages composed of temperature rising, ice melting, and ice shedding, among which the ice melting is the key stage consuming most of the ice-melting time. In this stage, an elliptic airgap is formed and widened gradually with an influence on the ice-melting time and the temperature of the conductor. The experiments in the artificial climate chamber demonstrate that the results of the presented model are consistent with those of the experiments generally, so it can be employed to estimate the parameters of ice melting in practical engineering as reference.

Nonlinear numerical simulation method for galloping of iced conductor

Nonlinear numerical simulation method for galloping of iced conductor

Nonlinear numerical simulation method for galloping of iced conductor

Based on the principle of virtual work, an updated Lagrangian finite element formulation for the geometrical large deformation analysis of galloping of the iced conductor in an overhead transmission line is developed. In numerical simulation, a threenode isoparametric cable element with three translational and one torsional degrees-offreedom at each node is used to discretize the transmission line. The nonlinear dynamic system equation is solved with the Newmark time integration method and the Newton-Raphson nonlinear iteration. Numerical examples demonstrate the efficiency of the presented method and the developed finite element program. A new possible galloping mode, which may reflect the saturation phenomenon of a nonlinear dynamic system, is discovered under the condition that the lowest order of vertical natural frequency of the transmission line is approximately two times of the horizontal one.

Instability trends of inertially coupled galloping Part I: Initiation

Abstract The objective of this paper is to investigate the trends of the dynamic behavior of a single iced conductor. Attention is focused not only on the initiation of galloping but also on boundaries where a periodic plunge or torsional motion emerge. Trends with respect to the iced conductor’s eccentricity and its inertia to mass ratio are particularly stressed. They are shown to be complicated because the individual influences of these two variables can be quite different, or even contradictory. Results are presented in a tabular form so that they can be applied easily to a specific problem.

AUTOMATED MEASUREMENT OF PROFILE DIMENSIONS

The design of a traversing mechanism is detailed which, when coupled to a microcomputer, is able to automatically measure the cross-sectional dimensions along an iced conductor sample. Calibration of the equipment is described and percentage errors are found to be less than a reasonable two percent.

Inertially Coupled Galloping of Iced Conductors

This paper is concerned with the galloping of iced conductors modeled as a two-degrees-of-freedom system. It is assumed that a realistic cross-section of a conductor has eccentricity; that is, its center of mass and elastic axis do not coincide. Bifurcation theory leads to explicit asymptotic solutions not only for the periodic solutions but also for the nonresonant, quasi-periodic motions. Critical boundaries, where bifurcations occur, are described explicitly for the first time. It is shown that an interesting mixed-mode phenomenon, which cannot happen in cocentric cases, may exist even for nonresonance.

A Geometrical Approach Assessing Instability Trends for Galloping

Although the galloping of an iced electrical conductor has been considered by many researchers, no special attention has been given to the galloping’s sensitivity to alternations in the system’s parameters. A geometrical method is presented in this paper to describe these instability trends and to provide compromises for controlling an instability. The conventional but uncontrollable parameter of the wind speed is chosen as the basis for obtaining the critical conditions under which bifurcations occur for a representative two degrees-of-freedom model. Variations in these critical conditions are found in a two-dimensional parameter space in order to determine the trends for the initiation of galloping as well as to evaluate the stability of the ensuring periodic vibrations.

Stochastic modelling and stabilization of galloping transmission lines

Abstract Galloping of overhead transmission line causes low frequency high amplitude oscillations resulting in line outages due to flashover between the phases, or between the phases and the ground wire. It is known that galloping is the result of aerodynamic instability of the iced conductors. In the commonly used approach to the analysis of galloping, the aerodynamic effects are represented by a deterministic coefficient in the system model. However, because of randomness of the wind velocity and direction, and of the shape of ice accumulation on the conductor surface, the aerodynamic forces could be better represented by a random process. In this paper, a stochastic model has been presented for modelling the galloping transmission lines considering the randomness of aerodynamic forces. Stochastic calculus has been used to obtain sufficient conditions for stability and instability. It has been shown that exponential stabilization of the conductor oscillations could be obtained by applying a suitable amount of mechanical damping to the conductor. The value of critical damping for the fastest decay of oscillations has also been obtained. The stability criterion given in this paper is based on rigorous analysis of the stochastic model. This gives a conservative estimate of the damping constant which can be relied upon under the worst possible disturbances.

Five Years' Field Trials of Detuning Pendulums for Galloping Control

Field trials of detuning pendulums for controlling galloping of iced conductors have been in place on operating single and bundle conductor lines for five years and have generated considerable observational data. A technique of analysis has been developed which permits these observations of galloping on conductors with detuning pendulums to be compared with those on similar untreated conductors for a range of single conductor sizes in the data bank. For single conductors between 25 mm (1 inch) and 50 mm (2 inch) in diameter on spans between 100 m (300 ft) and 400 m (1200 ft) in length, properly applied detuning pendulums are demonstrated to provide effective control of galloping. For other sizes of single conductors and for bundle conductors additional observations are required to confirm the present promising indications.

Influence of turbulence on the galloping instability of iced conductors

Previously reported wind tunnel dynamic tests on spring-supported models of transmission line conductors with crescent-shaped accumulations of ice, showed that the galloping instability of these models was significantly affected by turbulence in the air flow. The static aerodynamic coefficients of these models have now been determined in turbulent air flow, and a theoretical prediction made of the galloping instability. Good agreement has been obtained between this predicted performance and the previous dynamic tests. The method used for the prediction, and typical experimental data are presented in this paper.

Meteorological conditions associated with the full-span galloping oscillations of overhead transmission lines

The recorded phase-to-phase faults associated with the full-span galloping of CEGB overhead transmission lines over a 7-year period have been correlated in the form of histograms of number of faults as a function of wind speeds prevailing at the times of the faults. It is shown that, for bundled conductors, the results are in reasonable agreement with the theoretical predictions of Hunt and Richards for the minimum wind speeds necessary to cause phase-to-phase faults. 1 presented a theory for determining the maximum energy input from the wind into the full-span galloping oscillations of ice-accreted bundled overhead transmission lines. The main assumption made was that the galloping motion could be represented by a vertical oscillation which was sinusoidal in time. One of the conclusions of the paper was that, for any particular conductor and tower geometry, there is a critical wind speed below which oscillation amplitudes large enough to cause interphase clashing cannot be maintained. The critical wind speed is found to be a function of the maximum lift coefficient of an iced conductor or bundle of conductors,which can only be estimated using wind-tunnel models of ice-laden conductors. This is the biggest unknown in the theory, and should be borne in mind when applying the theory. At the time the paper was published, there was very little information available about the wind speeds prevailing at the times of full-span galloping of bundled conductors, and it was not possible to assess how close the critical wind speed was to the.actual lower-bound wind speed found in practice. This paper presents data collected from the CEGB transmission system over a 7-year period, and is a first attempt at examining the meteorological conditions under which largeamplitude full-span galloping occurs on bundled overhead transmission lines.

Nomographic Computation of the Ampacity Rating of Aerial Conductors

The prime objective is to develop a comprehensive and explicit method for computing the current-carrying capacity for either bare, covered, or iced aerial conductors. There have been many methods devised to compute ampacities. Moreover these methods are often quite involved and require the use of computers for their solution. The nomographic process encompasses more complex situations. It operates on the complicated nature of these formulations in a manner that reduces their complexity to a simple, accurate, and hence efficient system of computation. Intentionally, there is a vast amount of versatility built into this procedure whereby many ampacity-related parameters, for example, conductor temperature or wind velocity, may be computed easily and quickly. This development is designed to assist the reader in exploring the complete panorama of parameters or variables that manifest themselves in the science of current rating rather than in portraying a procedure needed to compute only ampere values. Furthermore, it is intended that computer programs would be used to solve problems involving a multitude of conductor sizes and/or ambient conditions, whereas the nomographic approach would, in essence, provide an analytical tool that can be drawn upon for the purposes of solving isolated ampacity problems.