Directional overcurrent relay protection system implementation on 8-bus system using Typhoon HIL Juan David Hernández Santafé*, Felipe Antonio Gómez Olaya*, Paulo Manuel De Oliveira De Jesús* Abstract: The coordination of directional overcurrent relays (DOCR) is a complex problem. Generally, optimization problems are posed using simplified positive se-quence network models. The 8-bus transmission system proposed by A.S Braga and J. Tome Saravia in 1996 has been widely used as a standard test case on DOCR to get optimal solutions. However, detailed three-phase network models are required in order to analyze the quality of the resulting relay settings obtained from optimization procedures. In this chapter, the 8-bus transmission system was implemented in Ty-phoon-HIL in order to evaluate protection system performance, considering system pre-fault conditions, load currents, current transformers (CT) saturation and the ef-fect of transient topologies. Protection engineers will benefit of the proposed imple-mentation to evaluate the quality of any directional overcurrent protection scheme, optimized or not, under realistic conditions. Keywords: Coordination of protective relays; Core; Pre-fault conditions; Directional overcurrent protections; Real time software; Simulation couplings; Transient currents; Transient topologies.