The influence of strong magnetic field on stress intensity factor of an interface crack is studied in this paper. The nonlinear piezomagnetic property and magnetostriction effect have been taken into consideration in the theoretical analyses. This multi-field coupled problem is solved through a sequential coupling approach. The perturbed magnetization caused by the deformation around the crack is solved under magnetic boundary conditions. After modified by the perturbed magnetization, the initial loads are updated with magnetic forces for iterative calculation. With this strategy, the distributions of the stress and displacement at the crack region approach to the real solution gradually. Numerical results show that the influence of the external magnetic field on fracture behaviors is not ignorable. For structures with interface crack serving in a strong magnetic field, e.g., the multi-layer welded structures in the Tokamak device, the magneto-elastic coupling effects have to be considered to deal with its fracture problem.
Partial discharge (PD) diagnosis is a crucial tool to assess the insulation condition of wind farm cables. Among PD diagnosis techniques, PD localisation is promising as it can provide target maintenance indicators on the insulation weak points of the cables. Accordingly, this paper developed a portable PD detection and location system for wind farm inter-array cables. The system consists of two non-invasive and lightweight testing units, which can be conveniently deployed on an energised cable, enabling highly efficient online PD diagnosis of the widely distributed inter-array cables. The system achieves accurate PD localisation of the energised cable via an improved double-sided travelling wave method. The method exhibits two superior features: the double-sided testing units are accurately synchronised via the joint application of Global Position Systems and a pulse-based interaction process, and a windowed phase difference method is proposed and integrated into the system to robustly estimate the time-of-arrival difference in low signal-to-noise ratio environment. Validation experiments were conducted on both a 10-kV cable in the laboratory and a real 35-kV cable in an on-shore wind farm.
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