IMPACT OF DISTRIBUTED GENERATION ON PROTECTION DEVICE IN THE CONTEXT OF DISTRIBUTION NETWORK

Abstract

The increasing integration of distributed generation (DG) into low voltage distribution networks has introduced significant protection performance challenges. Traditional non directional over current relays, designed for unidirectional power flow, often malfunction under DG operation due to changes in faults current magnitude, direction, and source contribution. This research investigates the impact of DG on relay performance and proposes effective mitigation strategy using coordinated and graded non directional relays. A 15kv radial distribution network with a total capacity of 24 MVA was modeled and simulated in DIgSILENTPowerFactory. A 6MW inverter based DG unit (solar PV and wind hybrid) was integrated at bus 47 to analyze its impact under various fault types (L-G, L-L, L-L-L) and locations. Three simulation scenarios were evaluated.1) based case (without DG), 2) DG integrated case, 3) mitigated case (with DG and 11 coordinated non directional relays). The performance was assessed using key metrics: fault current, relay operating time, coordination time interval (CTI), selectivity, directional behavior, and unwanted/missed trips. Results indicated that DG integration changed fault current, reversed current direction, and led to protection blinding, sympathetic tripping, islanding risk and loss of selectivity. After applying the mitigation scheme with 11 graded relays, selectivity fully recovered, and no false trips and missed trips occurred. The mitigation thus demonstrated that DG induced issues can be eliminated using only non-direction relays, provided proper coordination and setting adjustments are made. Furthermore, a practical method for current transformer (CT) ratio selection was developed to ensure adequate sensitivity without saturation under DG fault conditions. The key contribution of this research lies in showing that reliable DG integration can be achieved through analytical coordination and relay grading, avoiding the need for expensive directional or adaptive relays. The findings are highly relevant for distribution utilities in developing regions seeking low cost and technically viable protection solutions for networks with moderate DG penetration (<=25%).