Modeling Sudden Ice Shedding From Conductor Bundles
Sudden ice shedding from conductor bundles was modeled numerically and experimentally by improving the approaches proposed formerly for a single cable. The experimental study was carried out on a small-scale laboratory model of one span of a twin bundle. A numerical model of the experimental setup was developed using the commercial finite-element software ADINA. This model was validated by simulating: 1) the vertical cable vibration during former load shedding tests on a full-scale line of single conductors; 2) the bundle rotation on a full-scale twin bundle during former static torsional tests; and 3) the vertical cable vibration and bundle rotation at midspan during the present load shedding tests on a small-scale twin bundle. The coincidence of calculated and measured tendencies justified the applicability of the numerical model to simulate the vibration following ice shedding from bundled conductors in most cases. The model was finally applied to simulate sudden ice shedding from a full-scale span with a twin bundle. Simulation results showed that the application of spacers reduces the cable jump height during this vibration; however, a higher number of spacers in the same span does not decrease the angle of bundle rotation.
Numerical simulation on jump height of transmission line subjected to ice-shedding with different time intervals
The vibration of ice-shedding on overhead transmission lines will result in serious damage to tower-line system. In order to reveal the effect law of the different time parameter on the jump height of iced overhead lines after ice shedding, the conductor-insulator coupled finite element model was established, and the additional force method was employed to simulate the process of ice-shedding from overhead transmission lines, then the values of jump height were obtained for simultaneous total-span ice-shedding, unzipping ice-shedding, and assembling ice-shedding. Results from this study showed that, the difference between numerical simulation result and formula calculation result was negligible for simultaneous total-span ice-shedding. The dynamic response of unzipping ice-shedding is close to static unloading when the velocity was lower than 20m/s, the jump height was far less than calculated value by empirical formula, but the jump height of unzipping ice-shedding is close to simultaneous total-span ice-shedding effect when the velocity of ice-shedding is higher than 50m/s. The minimum jump height occurs when ΔT=T/2 for one-span assembling ice-shedding; and the maximum jump height occurs when ΔT=T/8, which may slightly greater than simultaneous total-span ice-shedding because of conductor coupling effect.
VORTEX-EXCITED VIBRATIONS IN BUNDLED CONDUCTORS: A MATHEMATICAL MODEL
Wind-excited vibrations generated by vortex shedding are very common in high-voltage overhead transmission lines. Although such vibrations are barely perceptible due to their low amplitudes (less than a conductor diameter), they are, however, extremely important since they may lead to conductor fatigue. Mathematical models are therefore necessary for the computation of these vibrations, in order to evaluate the risk of potential damage to the line as well as for studying the efficiency of damping measures. For single conductor lines, the socalled energy-balance method gives good results in estimating the vibration amplitudes. However, the problem becomes more involved for bundled conductors with spacer dampers, commonly used in high-power transmission in many countries, and a modified form of the energy-balance method is presented here. Singular perturbation methods are employed, along with the energetically equivalent standing wave amplitudes obtained from the modified energy-balance methods, to determine the bending strains at critical points. This gives an estimate for the maximum strain levels in a conductor, which can be very useful in the design of transmission lines and for the optimization of the corresponding damping devices. # 2002 Elsevier Science Ltd. All rights reserved. Of the different mechanical vibration phenomena in high-voltage overhead transmission lines, wind-excited oscillations of the conductors constitute a major issue. The most common of these wind-excited vibrations are those generated by vortex shedding in the frequency range of approximately 10–60 Hz. Thus, only these are considered in this paper. Although such vibrations are barely perceptible due to their lowamplitudes (less than a conductor diameter), they are, however, extremely important since they may lead to conductor fatigue. Mathematical models are therefore necessary for the computation of these vibrations, in order to evaluate the risk of potential damage to the line as well as for studying the efficiency of damping measures. The energy-balance method is commonly used to estimate the vibration amplitudes of single conductor lines Hagedorn 1980; Vecchiarelli et al., 1999; a more general overviewon the relevant publications can be found in these references. In the present, paper the method is generalized for the case of bundled conductors with spacer dampers. The main ideas of the mathematical model for a single conductor may be briefly described as follows. Consider the schematic representation of a single conductor line shown in Fig. 1. Since the length of the span is typically of the order of L ¼ 300–500 m, the wavelengths l of the vibrations are of the order of a fewmeters, and the sag only a fewpercent of the span, the sag can be neglected. Thus, the conductor may be modelled as a taut string with