This work presents the main types of materials and insulation systems used in medium voltage networks and aims to assess the characteristics of some types of measurement equipment, as the ultrasound detector and the interference radio detector, used in electrical inspections of power systems. Results are presented of the preventive field inspections and laboratory studies, besides computer simulations. Among the techniques used are explored the ultrasound inspection of distribution networks, by being a mostly used by concessionary of electricity. It was elaborated a inspection interface using LabVIEW, that provides the information online to the operator. In addition it was held the post-signal processing, whose objective is to make the inspection of determined devices less subjective, using Fourier transform techniques. The developed tool identifies the pattern of the signal to differentiate problems facilitating the field inspection.