Multi-user Expert System for Operation and Mainte- nance in Energized Lines Erika F. Moreno, Evelyn E. Pacheco, Víctor H. Andaluz and Álvaro S. Mullo. Universidad de las Fuerzas Armadas ESPE, Sangolquí - Ecuador {efmoreno1, eepacheco1, vhandaluz1, asmullo}@espe.edu.ec Abstract. The article presents the development of a multi-user application in vir- tual reality for the training and theoretical-practical training of electrical mainte- nance personnel in the operation of energized lines. The environment has a safety explanatory room in which users will know each of the rules and protocols ap- plied to perform maintenance maneuvers and operation of energized lines, a re- alistic work area of the electrical power system that starts from hydroelectric gen- eration and passes through transmission lines, subtransmission to reach substa- tions that raise or reduce the voltage for subsequent distribution. The environ- ment has been created using photogrammetry techniques, WorldComposer, CAD design tools, Unity 3D, DigSilent Power Factory and Matlab to provide realism of electrical system behavior, emulating failures and critical conditions caused by external and internal emergency events. Experimental tests show the effi- ciency of the system generated by human-machine interaction in which operators interact between themselves and the ambience, facilitate immersion in an envi- ronment that offers to contribute to the development of their risk-free collabora- tive skills and abilities. Keywords: Virtual Reality, Maintenance on Energized Lines, Electrical Power System, Photogrammetry, Unity 3D. Palabras clave: Realidad Virtual, Mantenimiento de Líneas Energizadas, Sis- tema Eléctrico de Potencia, Fotogrametría, Unity 3D. 1 Introduction Maintenance in industrial systems is a strategic factor to guarantee a high level of safety and productivity [1]. The development of adequate maintenance policies guarantees the efficiency of production plants in terms of quality to minimize costs and maximize the availability and performance of fixed assets [2]. Several maintenance policies have been introduced, such as fault-based (FBM), usage-based maintenance (UBM), condi- tion-based maintenance (CBM), design and output maintenance (DOM) and detection- based maintenance. Ideally, maintenance should be performed shortly before the asset fails, not too soon, but not too late either [1] [2]. The most common practice in the industry is preventive maintenance; a piece of equipment is regularly serviced while in operation so that it does not cause unplanned downtime. Predictive maintenance, on the