System Protection Coordination Study for Electrical Distribution System

System protection coordination studies are important in power system networks to ensure the continuity of service in the system. This paper presents relay coordination and tripping sequence of circuit breakers for Taylor's University Electrical Distribution System (TUEDS) using Electrical Transient Analysis Program (ETAP) by choosing appropriate relays and circuit breakers settings after conducting load flow and fault analysis to find the relay pick up current and plug setting multiplier. Two different buses were simulated for the three-phase fault to ensure the circuit breakers have proper tripping sequence and timing. The results obtained for transformer 2 load bus MSB 2 have short circuit value of 31.7 kA and tripping time for breakers CB-T2L as primary protection, CB-T2H, and CB-IF2 as backup protection is 30.6 ms, 472 ms, and 507 ms respectively. For transformer T4 load bus MSB 4, the fault current obtained is 46.8 kA and the tripping time for breakers CB-T4L as primary protection, CB-T4H, and CB-IF2 as back up protection are 30.7 ms, 196 ms, and 413 ms respectively. The back-up protection for each protective device is achieved by ensuring appropriate coordination time interval between the protective devices for a more reliable protection. The time-current characteristics curves (TCC) for relays and low voltage circuit breakers were presented to show the interrupting time of the devices based on the current level.