IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE) e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 10, Issue 1 Ver. I (Jan – Feb. 2015), PP 58-65 www.iosrjournals.org DOI: 10.9790/1676-10115865 www.iosrjournals.org 58 | Page The Reliability Study of 11-Kv Distribution Feeders: A Case Study of Idi-Araba Phcn Injection Substation Ignatius Kema Okakwu 1 and Oluwasogo Emmanuel Seun 2 1 PhD Scholar, University of Benin, Nigeria 2 Lecturer, Electrical and Computer Engineering, Kwara State University, Kwara, Nigeria Abstract: The frequent outages of power supply due to the occurrence of faults on the system constituents a major problem to electricity consumers in Nigeria. As it is being witnessed all around Nigeria, most commercial cities especially Lagos: Using 33-/11-kV Idi-Araba Injection substation, Mushin, Lagos as a case study, data containing number of faults on each feeders and their respective downtime were collected. This data collected were analysed mathematically to estimate the reliability of the injection substation for a period of five years. The results obtained from the analysis of the 11-kV feeders show that 2011 electricity supply was the most reliable with 81.18% of the system working without failure and 33-kV feeder shows a maximum reliability of 97.02% in 2007 working without failure. The percentage of the system working without failure for 11-kV over the period of five (5) years shows that the system was reliable with 63.61% out of 84.38% availability. Again, for the 33-kV feeder, the system was reliable with 93.39% reliability out of 99.01% availability. Keywords: Reliability, Availability, MTTR, Failure rate, Feeders. I. Introduction Electric energy occupies the top grade in the energy hierarchy. It finds innumerable uses in homes, industries, agriculture and even in transport. The fact that electricity can be transported practically instantaneously is almost pollution free at the consumer level and that its uses can be controlled very easily, make it very attractive as compared to other forms of energy. The per capita consumption of electricity in any country is an index of the standard of living of the people in that country. Nigeria’s economy, like that of many other countries in the world, should witness rapid energy usage, but over the years, electricity supply in Nigeria had been epileptic due to problems ranging from poor funding, lack of good policy from government, lack of commitment on the part of PHCN staff, hence, making Nigeria the largest importer of generators in the world. The electric power system networks are means by which the electric energy generated at the power stations are converted to the consumers. Almost two-thirds of the money invested by the utility company in supplying electric services to its consumer is spent in this division. The electric power network can be subdivided into two, namely; the transmission and distribution systems. The distribution system connects all the individual loads in a given locality to the transmission lines via switchgear equipment. The distribution system may be sub-divided into three, based on the voltage level as follows: primary distribution (33Kv), secondary distribution (11Kv) and tertiary distribution (415V three-phase or 230V single-phase). Hence, industries, individual, small and large consumers are serviced from the distribution network. Therefore, there is the need to improve the reliability of distribution network, due to the increasing dependability of human existence on electricity. II. Aim And Objectives The main aim of this research is to perform a detailed mathematical analysis on Idi-Araba Injection Substation (33-/11-kV) to estimate the reliability of the primary and secondary distribution networks. The objectives of this research work are to determine the failure rate (), the mean time between failures (MTBF) and reliability of the network. III. Index Of Reliability Reliability is a probability expression that needs to be quantified to make it suitable for scientific analysis. This quantification is carried out by introducing performance parameters which indicate the degree of reliability and are called indices of reliability. Some of them are explained below. (1) Failure rate (): This is the basic index of reliability. It is a measure of the frequency at which faults occurs. (2) Mean time between failure (MTBF): This expresses the average time, which elapses between consecutive failures of a repairable system of equipment.