1.0 Introduction
Distribution networks differ from transmission networks in quite a number of ways, ranging from voltage magnitude to the number of branches and sources. The number of branches and sources is much higher in distribution networks and the voltage magnitude lower. Its general structure of make up is quite different from that of the transmission networks.
A typical distribution system consist of step down transformer e.g. 132/11kv, at a bulk supply point feeding a number of cables. A series of step-down three phase transformers, e.g. 11kv/415v, are spaced in route and from these, the consumers are supplies three phase, four wire networks which give 240 single phase to house and other similar loads.
Also, large scale or industrial consumers could be supplied at 33kv or 11kv.
The objective of power system company is to maintain a continuous and adequate power supply to its consumers at a reasonable rate of return. In Nigeria, this objective is far from being met. Hence, there is the need to focus our attention on reliability as a way of assessing and improving the power system as well as optimizing our investment in the distribution network.
Reliability studies are performed to maximize the reliability, efficiency and safety of an electric power system.
It has been observed that a major part of service interruptions experienced by consumers has its origin in failure from the distribution system (mostly 33kv and below in Nigeria, with radial arrangement), and the distribution system reliability studies have been hindered due to the unavailability of component outage on the distribution system.
Hence, the need to maintain a reliable and effective distribution system using the available equipment on the system is very important and necessary.
1.1 Significance of the Study
The significance or relevance of this study are as listed below:
- Improve efficiency.
- Increase operating reliability.
- Improve system maintainability.
- Reduce operating cost.
- Evaluate the impact of adding new equipment.
- Optimize system upgrades.
- Identify sources of failures.
1.2 Definition of Terms
1.2.1 Reliability, R(t):
This can be defined as the capability of an equipment or asset to continue to perform its intended function under specified condition for a stated period of time. It is normally measured as the mean time between failures (MTBF) for each system. Dunn, 2002).
1.2.2 Failure Rate:
This is the number of faults or failures per unit time. The symbol is ?.
1.2.3 Mean Time Before Failure (MTBF):
This is the mean value of the length of time that elapses between failures.
1.3 Causes of Faults
The causes of faults include the following:
- Lightning strike
- Heavy wind
- Trees falling across wires
- Failure of insulators
- Vehicle collision with electric poles
- Illegal connections/operation by consumers
- Vandalization.
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