After reviewing the background of zero sequence impedance of pipe-type cables, the paper describes in general the longitudinal voltages induced in adjacent auxiliary cables due to a fault in power transmission systems. The magnitude of the induced voltage is influenced by the screening effect of the power cables. The screening factor and the impedance of the steel pipe have been measured in the laboratory by short-circuit tests on a 275-kV cable sample with a simulated ground return path. The results are used to illustrate the application in induced voltage calculations in a typical example.It is shown that, owing to the very low impedance of the steel pipe, it gives a very low screening factor, i.e., low longitudinal induced voltages in neighboring auxiliary cables. Hence an economical design of auxiliary cables may be used.
The conventional method for predicting the shape change of a surface crack in a round bar simply utilizes the Paris-Erdogan law with the least squares method using a certain shape assumption with excessive constraints. In this paper, a three-parameter model for a round bar subjected to tension is developed with fewer shape assumption restraints by employing a fatigue crack growth circles method. The equivalent stress intensity factor Δ K e based on both stress intensity factors along the current and new crack front is used to reduce the total number of increments. The results show that the proposed method has a good convergence speed and accurate prediction of crack shapes. The present method is validated by comparing the solution with other simulation solutions and experimental data.
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