Abstract:
Reliability improvement using suitable methods is very important to provide an adequate supply and with an acceptable quality to its customers. Power system stability should receive more emphasis in a rapidly developing nation like Ethiopia because energy is the main engine for any form of development. The present Dire Dawa Substation has encountered frequent power interruptions and power quality problems. The interruptions are caused mainly by short circuits and earth faults. The substation’s System Average Interruption Frequency Index and System Average Interruption Duration Index are 557.8 int/yr. and 233.15 hr/yr., respectively. This proves that there is a great reliability problem in the existing DDDN substation. which indicates that the current value is above the acceptable value by a large margin. As per the standard of the Ethiopian Electric Agency which set (SAIFI=20 and SAIDI=25). This reliability gap calls for searching for effective methods for improving the reliability. DDS has been supplied a 132kV transmission line is stretched into the substation then, the distribution network in the city has a primary voltage of 15 kV. In this thesis, the reliability of DDUF was done on a 15 KV system. Among different solutions to power system reliability problems, one of the modern and important techniques is integrating Distributed Generation (DG). Based on the availability of the resource, cost factors, emission level and utilization area PV is selected from other DG resources. The total price of PV is 7,936,892 $ and the size of a single DG is 1.2 MW, 729kw invertor and 5600Ah battery and this DG fed to the grid as a backup when there is an interruption. Simulation studied using ETAP software for reliability analysis is carried out and the cost of DG was calculated using Homer Software. In this thesis, the main focus is to install DG at the optimal feeder and size by using VSI and based on the sensitive load on the candidate feeder respectively as an objective to improve the reliability indices of the DDUF. Based on the calculation of VSI's best location among 15 outgoing feeders R2-G4 feeder was studied to investigate the effect of DG on reliability. And 50% (320.5 KW) Dire Dawa University load capacity was determined as DG size. As a result, the optimal placement of DG SAIFI and SAIDI is reduced from 680 f/yr and 270.7 hr./yr to 20.4 f/yr and 16.7 hr./yr respectively on the candidate feeder (DDUF). And the overall substation’s indices reduced from 557.8 f/yr and 233.2 hr./yr to 454.39 f/yr and 190.8 hr./yr respectively.
