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.
Experimental and numerical analysis of overhead transmission lines vibration due to atmospheric icing
Atmospheric icing is one of the main threats to overhead transmission lines in cold regions. The ice related loads may cause mechanical incidents, such as wire breakage, cable rupture, clamp slipping, cross-arm deformation and even tower collapse. Ice shedding may lead to dramatic vibration of lines and cause flashover or short circuit among ground wires, conductors and the earth. Therefore, to obtain the static and dynamic load characteristics of the overhead electric transmission lines is essential for transmission line design and operation. Also, it provides important information for health evaluation of transmission line components, and prediction of their remaining service life. In present study, a three-span full scale physical model of transmission line was established, with the span length of 50m-150m-50m. Ice shedding was simulated by sudden release of lumped mass. The mid-span jump heights were measured during different ice shedding scenarios, to quantizing the dynamic characteristics of lines. Then, finite element method (FEM) was employed for numerical simulation of ice shedding phenomenon. The comparison of numerical and experimental results confirms the feasibility and efficiency of the numerical simulation method in this paper. This study provides essential experimental data about ice shedding of full scale transmission lines, and is of great help for transmission line design and icing disaster alleviation.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.