Optimal coordination of directional overcurrent relays with non-standard multi-characteristics for power systems transient instability protection

Maintaining a stable operation of modern power systems, which are heavily loaded and strongly interconnected is a very complex task. This requires an optimal setting and coordination of protective relays considering the transient behavior of power systems. This paper proposes a new formulation of the optimal coordination of directional overcurrent relays (DOCRs) problem, considering power systems' transient stability and intelligent selection of non-standard characteristics. This problem is formulated as a mixed-integer optimization problem, taking into account non-standard relay characteristics and transient stability constraints, where the required power system parameters are calculated using Digsilent Power Factory Software. An enhanced version of a hybrid optimization method called: Hybrid Gravity Search Algorithm and Sequential Quadratic Programming (GSA-SQP), is proposed to solve the problem. The efficiency and performance of the proposed approach are validated on the 9-bus and 39-bus test systems considering various case studies. The obtained results show the efficiency of the proposed formulation to reduce the operating time of DOCRs with coordination and transient stability constraints satisfaction.