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Magnetic fields and the shielding efficiency of the shields of underground high voltage cables are studied in this paper regarding several shielding configurations and materials. Shielding efficiency and magnetic fields are computed for shields with the same mesh but from different shielding materials, such as aluminum, ferrite, metal, and steel. In order to get the best shield configuration depending on the source characteristics and the material, a conducting ferromagnetic region with various thickness values is considered as shielding. A finite element model is introduced to investigate the influence of the parameters of magnetic fields and the shielding efficiency of underground high voltage cables. Furthermore, the reduction of the magnetic fields with or without shieldings is also presented. The developed method is performed with the magnetic vector potential formulations and validated on a practical problem. [ABSTRACT FROM AUTHOR]

This paper deals with magnetic field mitigation techniques for underground power systems by using conductive or ferromagnetic shielding plates. Two new aspects are considered in this paper beside the shielding effectiveness analysis: the contribution to the series impedance and power losses due to the conducting set formed by the shielding plate/earth return path. A finite thickness ferromagnetic or conductive shielding is assumed buried parallel to the soil/air plane surface in order to model the induction magnetic field mitigation of a power underground cable system in flat configuration. An analytical method, appropriate to deal with possible optimization procedures, is used based on the magnetic vector potential for multilayered configurations where the shielding plate is treated as a different layer. Results for the magnetic field reduction factor at the soil surface are obtained for different shielding materials, different shielding thickness values, as well as different frequency values. Results are validated by employing the finite element analysis. [ABSTRACT FROM AUTHOR]

The paper presents an experimental investigation on the efficiency of different underground transmission/distribution line magnetic shielding techniques. Measurement results of magnetic field and temperature rise around the cable conductors are shown. An analysis of the thermal effects of each shielding technique on the line power capacity is presented. The experiments were performed on a test site where a real 138-kV underground cable section was built. The results provide useful information that can guide the designer when choosing the most suitable shielding technique according to the required shielding factor taking into account its impact on the line-rated power. [ABSTRACT FROM AUTHOR]

There are important concerns about the problems caused by high values of low-frequency magnetic field in urban centers. Two of them have received particular attention: the electromagnetic interference in sensitive equipment and the potential adverse health effects on human beings. In this way, many solutions to mitigate the magnetic field generated by these lines have been proposed. In this context, this work presents several computational results about the effectiveness of the main forms to reduce the magnetic field generated by underground power cables. The analysis addresses not only the field attenuation levels, but also the impact on the rated current due to the presence of shielding devices. From these results, it is possible to choose the best shielding arrangement for each specific situation, in order to achieve the required attenuation levels with the least ampacity loss. The thermal-magnetic model was implemented in the (free) software FEMM 4.2, which employs the finite element method. [ABSTRACT FROM AUTHOR]

Current monitoring can facilitate preemptive action in electrical distribution network, so as to relieve power congestion, improve transmission efficiency, and ensure network reliability. The non-invasive current sensing devices are promising since they do not require contacting hazardous high voltage and their installation is much easier compared with invasive current sensing devices. However, the existing non-invasive current sensing devices, such as current clamps and Rogowski coils are only applicable for measuring single-core underground power cables. In this paper, we established a non-invasive technique, that can monitor the currents of a multi-core underground power cable by measuring the emitted magnetic field around the cable surface. The additional magnetic fields generated by induced and leakage currents on the cables were firstly evaluated. Magnetoresistive (MR) sensors in a circular array were adopted to measure magnetic field around the cable surface, and a triple-layer shielding was designed to reduce the effects of external interference. Regarding intrinsic noise in MR sensors (e.g., 1/f noise and thermal noise), magnetic flux concentrators were supplemented to improve the signal-to-noise ratio. The developed platform was tested in a substation, and the reconstructed results closely matched the real geometrical configuration and current records of the tested cable. Apart from the non-invasive feature, the platform also shows great potential to improve the sensing capability of current amplitude and frequency compared with CTs by adopting MR sensors. [ABSTRACT FROM PUBLISHER]

This paper analyzes the thermal effects derived from the use of different screen shapes when shielding the magnetic field generated by underground power cables. A parametric analysis is developed to show the influence of the geometrical and the electrical parameters of the shield on the maximum temperature achieved by the power cables in order to analyze the impact of this technique on the ampacity of the line. A 2-D finite element approach is employed in this study to verify the performance of different types of screens (horizontal plate, reverse-U, and H-layout) in terms of shielding efficiency, overheating of the power cables, and operational costs. [ABSTRACT FROM AUTHOR]

This paper analyzes the possibility of using compensated passive loops to obtain a high mitigation effectiveness of the magnetic field generated by underground single-core cables. With that aim, several loops arrangements are simulated in a case study, including new ones called enchained loops, whose geometry reminds short-circuited conductors at both ends, but with the advantage of requiring smaller compensating capacitors. The results show a drastic spot reduction in several configurations, but with the drawback of high sensitivity to parameters. This aspect should be taken into account in the final design, so a design procedure is proposed that includes measures to alleviate this problem. Eventually, a comparison using shielding with high-conductivity material is provided. [ABSTRACT FROM AUTHOR]

This work present a modeling of underground isolated power cables through the coupled magnetic-Eddy current and thermal formulations solved using the finite element method (FEM). The governing magnetic and electric fields equations expressed in term of Magnetic- Vector-Potential (MVP) is strongly coupled with total Current density equation which include Eddy current (EC), source and Displacement Current densities which permit to take into account the skin and proximity effects. The computed (EC) density losses are introduced as heat source in the free transient thermal equation associated with the convection heat transfer. The thermal analysis solved using the iterative time-stepping algorithm and (FEM) lead to the temperature distribution at each step time. A single and multicircuit three-phase underground power cables arrangements are presented as the analysis devices in order to analyse the magnetic flux density and the time-space temperature. [ABSTRACT FROM AUTHOR]