In this work it is presented an energy harvesting system based on disperse magnetic energy produced by electric current across power line of a power distribution network in order to supply energy for devices in a wireless sensor network. The system is based on toroidal cores tested and validated with different materials and dimensions (five based on ferrite, seven based on nanocrystalline, seven based on iron powder) aiming harvesting optimal power device. From principles of magnetic ferromagnetic materials, it is discussed the magnetic field theory to obtain energy for supplying power to devices. It was implemented a prototype consisting of a test bench capable of emulating power-line high currents and of a power conditioning circuit. Test procedures were executed in three parts. The first was to determine the magnetic parameters (e.g. relative permeability and magnetic curve) of each harvester using a circuit able to measure core permeability in order to obtain B x H cycle. The second was to test a proposed power conditioning circuit composed of an AC/DC rectifier and a voltage regulator. The third, the experimental results were compared with theoretical ones. The obtained experimental results have been in agreement with theory, showing that the energy harvesting system is capable of supplying up to 315.6 mW from ferrite based core, 54mW from nanocrystalline based cores and 0.77mW from iron powder based ones, by capturing magnetic dispersion produced by a 15A current in the power line, which can be applied to various low power devices, mainly in wireless sensor network for data acquisition and control parameters of the power line itself.