### Literature Review
* Type of OC relays: In [29; 39; 40], the optimal coordination of non-directional OC relays has been considered. In [12; 56], different operation characteristic curves of non-directional OC relays have been analyzed in detail. The OC relays can be classified into three main types: instantaneous, definite-time, and inverse-time OC relays. If the measured current exceeds a tripping-current threshold, the instantaneous OC relay sends a tripping signal immediately to circuit breakers, while the definite-time overcurrent relay will send a trip signal after a pre-defined time-delay. The inverse-time OC relay operates with a typically mathematical function with certain parameters to form a protection curve as followed by IEC 60255-3 or IEC C37.112-2018 standards [57; 58]. The optimal coordination algorithm of OC relays usually focuses on the inverse-time function. In [59; 60], the admittance-based inverse-time OC relay is used to improve the sensitivity of fault detection in the DN and microgrids. In [61; 62; 63; 64], the voltage-based inverse-time OC relay is used to be more sensitive to different fault types and reduce the total operation time of relays. In [65], the single and dual settings of OC relays are proposed to increase the selectivity of the protection system under the high penetration of DGs into the DN. In general, the above-mentioned works only consider the inverse-time OC function as an objective function to be optimized, however, it can be proposed to combine the definite-time OC function with the inverse-time OC function to protect a DG-based distribution network. The reference [66] has solved this research gap, but how to demonstrate the reliability of calculated fault-current values in the DG-integrated distribution network has not been paying attention to. In fact, minimum and maximum fault-current values of each fault type are the basis to properly set-up the inverse-time and define-time OC functions in the protection system. * Coordination algorithms of OC relays: In [39; 54], two PSO (Particle Swarm Optimization) and GS (Gravitational Search) algorithms are used to calculate TDS multipliers and pick-up currents for the OC relays in a DG-contained DN. In [53], a microgenetic algorithm is used to calculate overcurrent protection settings under any change in the DN configuration. In [66], a Firefly Algorithm (FA) is applied to coordinate the definite-time OC functions and the inverse-time OC functions in the DN protection system. In [67], a continuous genetic algorithm (CGA) is used for the optimal coordination of OC relays in a ring-type distribution system. In [68], the Firefly and Chaotic Firefly algorithms have been applied to solve the coordination problem of OC relays. In [69], a modified PSO algorithm is proposed to calculate the optimal relay settings. Generally, the main objective of coordination algorithms is to achieve the possible minimum tripping times through the optimal parameter settings of each OC relay. Typically, this study proposes to use three very common techniques such as GA, GSA, and hybrid PSO-GSA (Gravitational Search Algorithm) to calculate the TDS multiplier and inverse-time curve coefficients for each OC relay in a DG-contained distribution network. To explain that, the GA is a well-known optimization algorithm, whereas the GSA and the hybrid PSO-GSA are recently developed and also applied for protection coordination of OC relays in the DG-contained DN because of high convergence to the global optimal solution with several different constraints [39]. Moreover, relay coordination results of the GA can be used as the standard results to compare with the results of the GSA and the hybrid PSO-GSA. * Directional OC (DOC) relays and coordination algorithms: In [17; 24; 44; 45; 46; 48; 49; 50], the optimal coordination of DOC relays in the distribution network has been performed. Reference [17] uses a simplex algorithm to solve the protection coordination of DOC relays as a linear programming problem.