A Novel Online Protection Scheme based on Hybrid Grading technique for variable Active Distribution Systems

Designing a fast, robust, and efficient adaptive protection scheme considering the presence of variability and uncertainties of the operating modes of an active distribution system is one of the main challenges in achieving the vision of a smart grid. To achieve such adaptive protection, various solutions have been proposed in the literature, among them, the online protection is one of the advanced approaches as it takes protective decisions based on the actual fault conditions instead of the pre-calculated data. This paper presents an online protection scheme where it proposes a novel method for coordination of the relays which is based on hybrid inverse-time and definite-time (HITDT) grading technique. This hybrid method amalgamates the advantageous features of both individual grading techniques (definite-time and inverse-time) and resolves different issues related to these grading techniques considering the presence of distributed generations. The key feature of the proposed method is that it simplifies the multi-constraints relays coordination problem by making it independent of the number of relays in a system. The proposed method is based on the logic that, for a hierarchy level, the relays must operate according to the relay that experiences a higher fault severity factor during a fault. The performance of the proposed scheme has been tested and validated for an IEEE 37bus test distribution system. The results show that by using this scheme, comparatively faster operating times of relays and online convergence of optimization with a reduced number of constraints can be achieved.