Fast and selective protection brings more security, reliability and stability in power systems. Accomplishing this task by deploying directional overcurrent relays is one of the main challenges in the active distribution network. Due to the presence of two-level fault currents, conventional methods fail to meet selective protection requirements. Tackling this issue renders the need for using the dynamic model for relays operation, which may result in miscoordination or increase the operation time of relays in large scale networks. Therefore, in this article, a new protection coordination approach is presented based on employment of the dynamic model of relays operation and using a new variable K in this model. The presented variable simplifies the optimization space of coordination problem and provides fast-response protection. On the other hand, new coefficients in the operation model of relays may cause mal-operation in normal conditions. Therefore, a new logic is also devised that can be implemented based on numerical relays. Since this logic requires to employ numerical relay, the proposed method is modeled techno-economically to provide fast and selective protection with the minimum number of numerical relays. This model is formulated as a multi-objective optimization problem and TOPSIS algorithm is used as a decision-making approach. Results are discussed in depth.
