Distribution System Expansion Planning answers the services to be mounted, so that therndistribution network fulfills the predicted load requirement to satisfy all operational and technicalrnconstraints. It is used to particular planning horizon, ensuring the consumer reliability and powerrnquality standards. The operating characteristics of modern power system are modified due to thernintegration of Distributed Generations which have noteworthy economic and technical benefitsrnsuch as, reduction of complications in expansion planning of distribution network, reduction inrnlosses, improving voltage profile, flatter of peak load and increase reliability. This thesis workrnmainly provides planning of Cotobie distribution substation with voltage sensitivity analysisrnmethods to facilitate the integration of Distributed Generation into the grid distribution network.rnThe results of Distributed Generation are presented to determine the appropriate places and therncapacity to make the distribution network highly reliable. It is shown that outgoing feeder no-4rnand feeder no-1 have the least tail end voltage sensitivity index of 0.00132 and 0.00221rnrespectively. Appropriate places are selected for the DGs and their ratings are determined on thernprinciple of minimum system power loss. The power capacity of DG for feeder no-1 is found tornbe 2.7MW and for feeder no-4 is found to be 4.5MW in MV feeders. Finally for Cotobierndistribution system reliability, voltage profile and power loss before and after DG integration wererncompared. The results showed a reliability improvement of 37.08%, voltage profile within limitrnof 0.95 - 1.05 p.u and active power loss reduction of 71.68% as well as reactive power lossrnreduction of 61.61%. In addition installing as backup a 6MW DG source in LV feeders results thernreliability improvement of 82.428%. So this result shown that even if load demand increases 8.8%rneach year then DG units are able to meet the demand requirements until year-5.