CHAPTER ONE
INTRODUCTION
1.1        BACKGROUND
Electric power system is basically set up to supply electricity with little or no interruptions to its customers. The number of interruptions that occur while the system performs its intended function is part of what determines the overall reliability of the system. The other factor that determines its reliability is the quality of electricity delivered. Furthermore, the capability of a power system to continuously deliver quality electricity means that the customers are satisfied and the electricity providers are having favorable returns on their investment as they continue their business of supplying electricity. As electricity consumption has become an important factor that affects the drive needed for technology to grow and to facilitate the development of modern society, it is very important therefore to take seriously the issue of reliability of an electric power system.
Generation, transmission and distribution are the three subsystems of an electric power system. At the generating station, electricity is generated and transmitted through the high voltage transmission lines to the distribution substations. The distribution substation system considered covers the electrical system between the substation fed by the subtransmission system and the supply line to the consumers’ meters i.e. 11kV to 0.415kV transformation (Theraja and Theraja, 2005). The distribution substations are usually sited relatively near the customers for effective delivery, monitoring and maintenance of the substation and the customer end and are usually referred to as secondary distribution substation system. Distribution systems basically serve as the link from the distribution substation to the customer. Reliable and safe transfer of electricity to the customers covered by the distribution area is ensured by this system and is the main subject studied in this dissertation.