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.
Jump height of overhead-line conductors after the sudden release of ice loads
A series of tests was performed on a five-span section of 132kV line to determine the jump height of the conductors after the release of simulated ice loads from the centre span. The use of semitension assemblies at the suspension towers reduced the maximum jump height compared with that obtained with standard suspension-insulator strings, but did not prevent the phase conductors from passing dangerously close to each other. The importance of the sag in determining the jump height is stressed, and experimental and theoretical values for sag and jump height are compared. It was shown experimentally that the large sag differences resulting from some arrangements of ice loading brought phase conductors close together, and that the clearance to ground of the bottom conductor of the loaded span was reduced below the safety level for ice loads in excess of 1 lb/ft. It is concluded that, with heavy ice loads, phase-to-phase flashover can only be prevented by ensuring sufficient horizontal separation between phases.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.