Optimal user-defined directional overcurrent relay coordination considering different operating modes of microgrid

R Tiwari and R Chitranshi and D Jaiswal and P Dubey, INTERNATIONAL JOURNAL OF GREEN ENERGY, 22, 3045-3062 (2025).

DOI: 10.1080/15435075.2025.2482760

A microgrid's fault current magnitude depends on its operational mode, specifically whether it is grid-connected or islanded. Typically, we deploy distinct protection schemes based on the fault current magnitude in a given mode. Adapting the protection scheme becomes imperative when there is a change in the microgrid's operating mode. This process can be both challenging and time-consuming. This study introduces a common optimal protection scheme for user-defined directional overcurrent relays (UD-DOCRs) to address this challenge. The proposed protection scheme incorporates UD-DOCRs enhanced with two additional optimization variables: relay characteristic coefficients (lambda, eta). Along with the time multiplier setting (TMS) and plug setting (PS), these coefficients are crucial for choosing the best relay characteristics that meet the IEC-60255 standard. This article expresses the relay coordination problem as a non-linear programming (NLP) problem. It utilizes the genetic algorithm (GA) and the gray wolf optimization (GWO) algorithm to obtain the optimal relay settings. To showcase the effectiveness of the proposed protection scheme in comparison to existing techniques, this study considers the 7-bus mesh and 9-bus radial benchmark systems. The findings reveal that, in contrast to GA, the GWO-based approach significantly mitigates the issue of relay miscoordination.

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