Identification of Equivalent Source System for electromagnetic field pollution evaluation

In the design of extremely low frequency magnetic field shielding, the knowledge of the source data, like current values and space locations are required. Frequently these information are not available and only source types are known and their positions can be roughly predicted. The uncertainty on the source system geometry can be due to: inaccessibility of the source region, for instance because of different ownership or to a fuzzy definition of the geometric position of wiring, for instance when a bunch of wires is placed in a duct. In order to mathematically model the magnetic field created by actual sources, a reconstruction of an Equivalent Source System (ESS) has to be devised. This problem has already been treated in the literature [1,2,3]. All proposed techniques are based on the subdivision of the space in two parts: the field region and the source region, which is the region containing all the sources (power lines, transformers, panels, etc.). Moreover, the proposed procedures suggest how to evaluate an ESS which is able to generate in the field region the same field distribution produced by the actual sources. The above suggestions have been collected into a new procedure which performs the composition of magnetic fields having cylindrical and spherical like configurations which are suitable to represent respectively multiconductor power lines and transformers or panels. Starting from a qualitative knowledge of the source dispositions and types, the proposed procedure is able to compute the main parameters of equivalent sources which minimize a stated difference (norm) between actual and reconstructed field. The computations are based on suitable solutions of inverse problems. The case of a substation is used as a test case for the proposed approach.