Time-domain protection relays have gained importance in modern transmission networks since they are able to increase the system stability margins by accelerating the fault clearance procedures. However, as this kind of function is in some aspects new for protection engineers, the modelling and simulation of time-domain relays have been topics of interest to utilities. In this study, a modern time-domain protection relay is modelled and simulated. To evaluate its performance, a wide variety of fault scenarios (882 fault cases) is simulated using the alternative transients program. The obtained results show that the behaviour of the implemented model is very close to that reported by the time-domain relay manufacturer.