An implementation of current differential relay and directional comparison relay using EMTP MODELS

In contrast to the conventional electromechanical relay and static relay, the algorithm of a digital relay which can execute a variety of operations is also more complex; this necessitates a more in-depth verification of the digital relay algorithm. More recently, this has been done through software simulation. Power systems are simulated using EMTP, while relay models can be modeled using any high level language or available software package, such as MATLAB, FORTRAN, C, etc. The interaction between power system and relay models is implemented by using model interface. Methods of model interface are classified as playback or open-loop simulation, and real-time or closed-loop simulation. This paper presents an implementation of the current differential relay and the directional comparison relay using EMTP MODELS based on closed-loop simulation tools. Because EMTP MODELS is a PC-based closed-loop simulation tool, simulation can be tested dynamically, and also the cost is low. The current differential relay and directional comparison relay are realized and they are interfaced with a test power system. Their performances are evaluated for various fault types, fault distances, etc.