Study of the Influence of Underground Power Line Shielding Techniques on Its Power Capability
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Study of the Influence of Underground Power Line Shielding Techniques on Its Power Capability Marco Túlio A. Êvo1 · Hélder de Paula2 · Ivan José S. Lopes2 · Renato C. Mesquita2 · Diogo S. C. Souza2
Received: 3 August 2016 / Revised: 27 January 2017 / Accepted: 25 March 2017 © Brazilian Society for Automatics–SBA 2017
Abstract 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. Keywords Magnetic field · Shielding · Underground power cables · Finite element method
1 Introduction To agree with laws and regulations concerning the maximum allowed magnetic field levels, the presence of shielding devices is oftentimes necessary. In the particular case of
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Marco Túlio A. Êvo [email protected]
1
Federal University of São João del Rei–UFSJ, 36307-352 São João del Rei, Brazil
2
Federal University of Minas Gerais–UFMG, 31270-901 Belo Horizonte, Brazil
underground power cables, many technical solutions have been proposed to mitigate the resulting magnetic field, such as (i) conductor management, (ii) passive and active compensation loops and (iii) shielding by metallic materials (conductive or ferromagnetic). A good review of these solutions is presented in C4.204 (2009). However, the presence of additional elements near the power cables may cause a temperature rise of the conductors, due to the Joule losses caused by the eddy currents induced in the shielding and also hysteresis losses, in the case of devices made of ferromagnetic materials. Since overheating can damage the cables insulation, a derating of the line ampacity may be necessary to ensure its safe operation. Furthermore, aside from operating as additional heat sources, shielding equipment modifies the heat exchange conditions in the line surroundings. In this context, a shielding method should thus meet the required attenuation levels but, at the same time, influence as little as possible the line current rating. Due to the complexity of the problem, the computation of the magnetic field and, thus, the shielding effectiveness requires the use of numerical techniques as discussed in del Pino Lopez and Romero (2011b
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