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See detailInfluence of contact resistance on shielding efficiency of shielding gutters for high-voltage cables
Koroglu, S.; Sergeant, P.; V Sabariego, Ruth ULg et al

in IET Electric Power Applications (2011), 5(9), 715-720

The shielding of buried three-phase high-voltage power lines can be done by placing them in conducting ferromagnetic U-shaped gutters covered with plates. In case of a perfect electrical contact between ... [more ▼]

The shielding of buried three-phase high-voltage power lines can be done by placing them in conducting ferromagnetic U-shaped gutters covered with plates. In case of a perfect electrical contact between adjacent gutters and between adjacent cover plates, induced currents in the shield efficiently reduce the magnetic field generated by the cables. As however a perfect contact cannot be guaranteed, in practice, it is useful to quantify the effect of a defective electrical contact on the field reduction. From two-dimensional/three-dimensional finite element computations and experiments, the influence of the contact resistance on the shielding efficiency is investigated, as a function of the ratio of axial length to height of the shield elements. Furthermore, the effect of other parameters on the shielding efficiency is studied: the ratio of axial length to height, a parasitic air gap between the gutter and the cover plate and the type of the shield material. It was found that a low contact resistance deteriorates much more the shielding in case of an aluminium shield than in case of a steel shield. As expected, the effect is larger for shield elements with relatively short axial length with regard to the other dimensions. Nevertheless, the effect remains quite significant for aluminium shields with practically convenient dimensions. [less ▲]

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See detailAnalysis of perforated magnetic shields for electric power applications
Sergeant, Peter; V Sabariego, Ruth ULg; Crevecoeur, Guillaume et al

in IET Electric Power Applications (2009), 3(2), 123-132

The shielding performance of perforated magnetic shields for electric power applications is described. The shielding of an axisymmetric induction heating device is studied as a function of frequency ... [more ▼]

The shielding performance of perforated magnetic shields for electric power applications is described. The shielding of an axisymmetric induction heating device is studied as a function of frequency, number of perforations and dimensions of the perforations. From the numerical point of view, the perforations cause the numerical model to be 3D. A numerical optimisation is carried out to find the optimal geometry with respect to the shielding factor and the volume of the shield. For the optimisation, two approaches are presented. The first approach is fast and easy-to-implement, but has limited accuracy. It uses a classical 2D axisymmetric model where the perforations are approximated by ‘axisymmetric air gaps’ resulting in a segmented shield. It is shown how to modify the 2D model to obtain results that are similar to the ones of a 3D model. The second approach is more accurate although quite fast, but more difficult to implement. It combines a 3D thin- shell finite element model with the unmodified 2D model in a space mapping optimisation algorithm. The validation of both models is based on experimental work for an unperforated shield and for the optimised perforated shield. [less ▲]

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