The growth of the economy of a country is directly linked to the evolution of the electrical system that supports its greater demands for energy. The evolution of this system means investing in expansion, such as acquisition of new generating plants and transmission equipment. With the growth of electrical systems, there was a large increase in interconnection networks, and this has brought a very complex operation and control of them, especially in situations of abnormality, so its reliability has become a decisive factor. For this to be achieved it is essential that the generation, transmission, distribution and consequently operate their equipment in order to minimize possible performance failures. The power system operates at steady state most of the time, however, may be subject to disturbances and these act on the equipment connected to it. Among the many problems caused due to some disturbance can cite the surge and transient voltage. Thus, an electrical system must be capable of supporting a range of disorders without interfering in energy consumption without compromising their equipment. In order to investigate the cause of these failures, there were some maneuvers at the substation, measuring transients generated in order to evaluate the effects of these phenomena on the equipment. This course is designed to work in order to use the case of a substation as a reference for the study of voltage transients in electric power system. This study will be done in particular in power transformers.