Paper Details

Meshed and closed-ring medium-voltage networks rely on directional overcurrent relays (DOCRs) whose time multiplier settings (TMS) are coordinated for a fixed source configuration. Connection of distributed generation (DG) alters fault current magnitudes and, more critically, creates new primary/backup relay pairs that did not exist in the original network. This paper formulates DOCR coordination as a linear programming (LP) problem and evaluates three setting philosophies on a 33 kV, six-bus ring network with two synchronous DGs: (i) conventional settings optimised without DG, (ii) adaptive settings re-optimised for each DG state, and (iii) a single robust setting that satisfies coordination constraints for both states simultaneously. With 10 MVA DG at each of two buses, the conventional settings violate the 0.3 s coordination time interval (CTI) for 8 of 12 relay pairs, with negative CTI (backup faster than primary) for the two newly created pairs. Adaptive settings restore full selectivity but cause 4 violations if applied while DG is disconnected, highlighting dependence on reliable DG-status detection. The robust setting achieves zero violations in both states at the cost of 19.1% higher total primary operating time with DG and 67.9% without DG. A sensitivity study over 0–20 MVA identifies the DG size at which new relay pairs emerge; inverter-based DG and CTI-margin sensitivity are also examined, and practical implementation through IEC 61850 setting groups is discussed.

Nidhi Y. Savjani, “Optimal Coordination of Directional Overcurrent Relays in DG-Integrated Meshed Distribution Networks: Linear Programming Formulation and Robust Settings”, International Journal of Advance Engineering and Research Development (IJAERD), Vol. 10, Issue 8, pp. 1-7, February 2024, DOI: NA.