The application of virtual reality (VR) technologies is beneficial to the training related to industrial processes. Mainly because the technologies allow training complex threatening tasks within a safe environment. The interactive three-dimensional (3D) representation of a real world seems to be a more effective learning medium than other traditional tools. This paper presents the development and implementation of a training environment based on VR, applied to the maintenance of medium-tension overhead live-lines in power distribution networks. The architecture of the virtual environment includes three main components: the virtual warehouse of equipment, materials and tools; the interactive 3D environments; and a course management system. The system consists of 43 maintenance maneuvers, including the application of different techniques and equipment. It has three operation modes: learning, practice, and evaluation, which can be accessed according to the trainee's level of knowledge. The virtual environment is currently used to support training of thousands of power line operators with excellent results. The aim of the system is to improve the technical skills of operators and minimize safety risks while operating power distribution networks. The system has allowed a substantial reduction of the accident rates during live-line maintenance.