STUDY THE IMPACT OF DISTRIBUTED GENERATION ON THE RELIABILITY OF LOCAL DISTRIBUTION SYSTEM (Case study: Motta Distribution Substation)

Abstract

Electric distribution system power quality is a rising concern. Customers require higher quality service due to more sensitive electrical and electronic equipment‟s, and effectiveness of a power distribution system is measured in terms of efficiency, service continuity or reliability, service quality in terms of voltage profile and stability and power distribution system performance. The present Motta distribution substation has encountered frequent power interruptions and power quality problems. The interruptions are caused mainly by Permanent Short circuit (PSC), Transient Earth fault (TEF). There are also planned outages for operation and maintenance purpose. The substation‟s System Average Interruption Frequency Index (SAIFI) and System Average Interruption Duration Index (SAIDI) are 806 and 1,394.145, respectively. The substation is not reliable by the standard of Ethiopian Electric Agency (EEA) which set (SAIFI =20 and SAIDI= 25). This reliability gap calls for searching of effective methods for improving the reliability of the distribution system. This thesis presents impact of DG on reliability assessment at Motta distribution substation of 230/33 transformer two 33 kV radial outgoing feeders distribution and the base case reliability analysis using Monte Carlo and analytical enumeration system and has high loss of money that is 0.438 M$/a and 0.444 M$/a respectively for utility but Monte Carlo analysis is better than that of Analytical Enumeration. The improved reliable power distribution is due to the use of proper size and site of DG at the low voltage profile value bus of the distribution system by using probabilistic Monte Carlo simulation of reliability analysis and that of Enumeration analysis of the system using DIgSILENT power factory software. The NPC of DG is 20,831,473.21$ which optimized using HOMER software at the required size and the reliability of the distribution system is improved after the use of DG that is reducing SAIFI, CAIFI by 97.8%, and SAIDI by 76%, increasing ASAI by 14.38% and reducing ASUI by 76% and reducing the total power loss to 0.32 MW. The cost analysis is done on this thesis by using the Monte Carlo reliability analysis output and the DG total net present cost (TNPC) so the payback period is less than five years that is 4.28 years which means that the project is profitable