Resumen
One of the most complex disciplines in electrical engineering is power system protection which requires not only the proper understanding of the different components of a power system and their behaviours but also a good knowledge and analysis of the abnormal circumstances and failures that can occur in any element of a power system. Moreover, the rapid changing and development in relays principles as well as in their technologies are additional factors that oblige those people working in the field to expand and update continuously their knowledge. In this paper, we shed light in the evolution of protective relays since the onset of electrical energy to currently. We try also to foresee the future prospects and trends in this area.