Magnetic field shielding optimization in underground power cable duct banks

• A shielding cost optimization process is proposed combining finite element models and genetic algorithm.
• The magnetic field in the area of interest is minimized without overheating the power cables.
• The effect of different materials, phase configurations, shield geometry and losses is analyzed.
• Cost-effective conductive/ferromagnetic shieldings are derived for two-circuit underground duct bank.
• The effect on the shield performance of adding a new circuit in a previously shielded duct bank is analyzed.

In this paper, an optimization process, based on a genetic algorithm, is presented for the minimization of the cost (including losses) of ferromagnetic and conductive shields. The purpose of these shields is to maintain the power frequency magnetic field generated by underground power cable duct banks below a certain threshold, without limiting the ampacity of the mitigated cable. Both horizontal and reverse-U shielding geometries are tested through their application to a case study composed of 9 (3 × 3) ducts where two balanced in-phase three-phase circuits are arranged in three configurations: vertical, horizontal and triangular. The area to be shielded is located above ground surface at one side of the trench axis, where dwellings are usually present. The associated electromagnetic-thermal problem is solved in the optimization process by means of the finite element method. The most suitable solutions are identified, by highlighting the key features of each shield (material and geometry). Further scenarios, such as the addition of a third three-phase circuit in the shielded duct bank, are also analyzed.