A New Method for Optimal Coordination of Overcurrent and Distance Relays

The protection of the electrical power system is a complex task, especially at the level of the transmission system, because according to statistical indicators, this is where the greatest number of faults occur. The protection of transmission lines can be performed by several protection schemes. Among them, those that use relays with distance and directional overcurrent functions, which must operate in a coordinated manner. However, performing the coordination between these relays is not trivial and, with the use of conventional methods, it becomes rudimentary and laborious. Here, a new method was proposed, in which the coordination task between the overcurrent and distance functions was treated as an optimization problem based on Genetic Algorithm. For this, in the objective function developed, a new decision variable was inserted, called reverse zone time, applied as a backup in the conventional distance function of the relay. In addition, the value of the coordination interval between the overcurrent and distance functions of the relays was varied, seeking to evaluate the influence of this parameter on the time of the second zone of the distance relay. The proposed method was tested in a standard network of the 8-bus electrical system and the results presented proved its efficiency, as it allowed the reduction of the operating time of the overcurrent and distance functions of the relays.