Browsing by Author "Mengistu, Asres"

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    Design and Simulation of Gas Insulated Substation (GIS) for Electrified Railway System: Case study of Shiro Meda
    (Addis Ababa University, 2016-06) Mengistu, Asres; Mengesha, Mamo (PhD)
    Nowadays the demand for Gas Insulated Substation (GIS) is increasing over the world for efficient utilization of electric power and space. In this thesis a gas insulated substations is investigated or studied since they are more advantageous though, they use same protective devices or equipment when compared to air insulated substations. They are compact, requiring little maintenance, more reliable, have longer service life (more than 50 years) and safer. The compactness is due to the use of SF6 gas, which has high dielectric strength at moderate pressure for phase to phase and phase to ground insulation. Gas insulated substation system creates a vision of the future more efficient substations which includes various technical, economic and environmental criteria, such as reliability, cost, interoperability, re-configurability, security, controllability and flexibility need to be considered. In this one of Addis Ababa Light rail transit (LRT) gas insulated substation has been studied, analyzed and compared to conventional air insulated substation. This thesis work presents the design and simulation of gas insulated substation for the case of Shiro Meda. For this purpose, all the necessary electrical parameters data are collected through literature survey and from Ethiopian electric utility at the same time major components of gas insulated substation such as bus bar is designed consequently volume of SF6 is calculated. For designing a substation it is crucial to know the maximum value of short circuit current of substation and load flow analysis. For this purpose Electrical Transient Analyzer Program (ETAP) power 12.6.0 version has been used for numerous fault condition in 3 phase132kV gas insulated substation. The load flow analysis and short circuit for different bus have been done and the result is within limit according to the IEC 60909 and IEC 61363 standard. However, our design results 12.5 and 90 and 92% reduction the cost of maintenance, space and operation by 12.5 and 90 and 92% respectively compared to air insulated substation.
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    Social Psychological and Perceived Situational Factors Related To Football Fans' Aggression Among Ethiopian Coffee and Saint George Football Fans in Addis Ababa Stadium
    (Addis Ababa University, 2010-06) Mengistu, Asres; Dessie, Yekoyealem (PhD)
    This study set out to assess the following: (1) Relationship between Social psychological factors (id entification and de-individuation) and fan aggression, (2) Difference in aggression among fans' different levels of identification (3) Differences in aggressive behavior of football fans across s ocia-demographic facto rs. (4) Situational factors (venue, event, and staff variables) predicting fan aggression, and (5) Association between de-individuation and situational factors. A random sample of spectators (N = 220) at football league game in Addis Ababa Stadium were selected and completed a survey designed to identify or measure the aforementioned variables.) The data was analyzed using s tatistics including, t-test, descriptive mean comparison, one-way analysis of variance, pearson correlation, linear and multiple regression. Linear regression showed that fan identification predicted fan aggression. Consistent with previous studies, highly identified fans were more likely to behave aggressively at games than moderately identified fans and lowly identified fans . Multiple regression indicated that de-individuation components: anonymity, arousal, group size, and loss of self awareness emerged as significant predictors of fan aggression respectively. Venue-situational factors: stadium location, temperature, noise level, and seating arrangement were rated important variables respectively. The two club fans did not show significant differences in the above venue variables. Event-situational factors: crowd demography, alcohol availability, performer behavior, event significance, and event duration were found to be important in contributing to aggression. The two clubs fans significantly differed in event s ignificance, performance quality, crowding, and event duration among the event variables. Staff-situational factors: experience, communication, and training were rated important contributors to aggression for both club fans. The t- test also revealed that the two clubs fans significantly differed in communication among, presence, and experience of the police officers in their contribution to fan aggression. From socio-demographic factors, age and longevity of fandom were found to have significant effect on aggression. The research results indicated that those fans aged between 21-25 tended to show higher levels of aggression than any other age category. Fans with 6-10 years of fandom tended to experience lower levels of physical aggression than fans with more than 15 years of fandom. Analysis us ing a Pearson correlation matrix showed a pos itive correlation between de-individuation and situational factors: staff, event, and venue characteristics.