This paper assesses the reliability of a Nokia N1650 mobile phone charger used in Zaria, Nigeria. The Part Stress Method was employed to assess the reliability of the system. Data on the failure rate of the system components were used, with special considerations given to factors like environment of use, quality of power supply and service personnel. A comparative assessment was made on the system, when operated within the Zaria environment and when operated within the country for which it was designed for (China).The result shows that a lower reliability level is associated with the use of the system in Zaria, Nigeria as compared with the reliability level when in use in the country for which it was designed for. The Mean-Time to Failure of the system which is the time it is expected to function without failure (MTTF) in Nigeria is 1 years as against 10 years in China. The ratio is 10:1 in favour of the designed country. The ratio of the failure rate of the system is also 10:1 in favour of the designed country, meaning it fails ten times faster in Zaria environment as compared to the country for which the system was designed for. These are accounted for by higher variation in the environmental factors such as temperature, poor power quality, and poor maintenance culture in the applied environment.
In this study, optimal distribution network protection coordination scheme with directional over current relays is developed. In addition, impact of optimally placed Distribution Generation (DG) on the protection coordination scheme is subsequently evaluated using relay Coordination Time Interval (CTI). As such, the study is carried out in two stages. In the first stage, optimal relays settings (time dial settings and pickup current) are determined. While in the second stage, the maximum DG penetration level with changes in the protection coordination is evaluated. Particle Swarm Optimization (PSO) algorithm, due to its faster convergence speed, is applied in both stages. The technique is implemented on the distribution section of the IEEE 14-bus and IEEE 30-bus systems and simulated in MATLAB. The simulation results obtained are compared with that obtained using hybrid Genetic Algorithm (GS) – Nonlinear Programming (NP) approach using relays pickup current and operating times as performance metrics. For the IEEE 14 bus system, the developed PSO-based relay coordination has reduced the relays pickup current and operating times by roughly 28% and 32% respectively compared with the hybrid GA-NLP technique. The optimal locations of the DGs are found to be bus 5, 8 and 12 which result in CTI of 0.233sec. While in the IEEE 30 bus system, the developed relay coordination has reduced the relays pickup current and operating times by roughly 31% and 34% respectively compared with the hybrid GA-NLP technique. Similarly, the optimal locations and sizes of the DGs are found to be bus 19, 26 and 30, which result in CTI of 0.462sec.
Frequent and major power interruptions cause many concerns. Assessment of customer power supply reliability is an important part of distribution operation and planning. Many factors are responsible in the reliability of power network; design, construction, operation and maintenance which have their combined effect to overall performance of power network reliability. Analysis of outage data from both OH and UG distribution system of Abuja network is carried out assess their reliability indices. Predictive assessment of distribution reliability indices can be used to identify areas that have poor reliability so that appropriate approach can be taken in the system design and implementation. This paper presents assessment of reliability indices in a practical radial distribution network particularly with the interest of comparison the reliability of OH and UG distribution system. UG is more reliable than OH but takes longer duration in fault restoration.
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