This paper presents the finite element analysis of the magnetic field of underground power cable lines from medium to high voltage. The main goal is the comparison of various methods of magnetic field management with special attention to its thermal effect and to multiple feeder power lines. The combined electromagnetic and thermal FEA simulation clearly shows that magnetic field minimization is contrary to the cable temperature. The effectiveness of the classical U-shaped magnetic screen made from thin highly permeable alloy is investigated. In addition, the newly proposed tube-formed magnetic screen is thoroughly simulated taking into account both magnetic and thermal effects.