Browsing by Author "TESFAYE BELAY"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    ASSESSMENT AND ENHANCEMENT OF THE TRANSIENT STABILITY OF DFIG BASED WIND FARM USING ANFIS (A Case Study of ADAMA II Wind Farm)
    (Hawassa University, 2021-12-18) TESFAYE BELAY
    Wind power is the greatest existing and used form of renewable energy in the world. Mixing the different wind farms to the national grid introduces new challenges regarding power system stability, among power system stability concerns; transient stability is one that significantly affects the grid. The objective is to assess and enhance the transient stability of DFIG based on wind farms, to model PI control for speed and slip control generator, to improve transient stability using thyristor control series capacitor (TCSC), to conduct during pre-fault, during fault, and post fault conditions. The methods to gathering data are through review of different papers, by asking the site workers, preparing questions for the worker, and from nameplates of equipment. The result consists of four conditions, the first condition is pre-fault conditions, the systems have no disturbance, the second condition is during a fault condition, all systems are disturbed, the third condition is posted fault conditions in this systems have no disorder and the fourth is the improvement of the systems by using TCSC, TCSC is injecting reactive power to the fault area and remove the fault from the systems or back to normal operations. Generally, stability has contained three scenarios pre-fault, during the fault, and post-fault condition. In Matlab Simulink, the pre-fault and post-fault have no disturbance, but during fault conditions, the systems disturbed and the disturbed systems are solved by TCSC at the improved conditions of the systems.
  • No Thumbnail Available
    Item
    PREVALENCE OF RETAINED FOETAL MEMBRANES AND ASSOCIATED RISK FACTORS IN CROSS BREED HOLSTEIN FRIESIAN DAIRY COWS IN SMALL AND LARGE SCALE DAIRY FARMS OF SELECTED DISTRICTS OF SOUTH AND OROMIA REGIONAL STATES
    (Hawassa University College of Agriculture, 2020) TESFAYE BELAY
    A retrospective study was carried out to analyze the prevalence and risk factors associated with retained foetal membranes (RFM) in crossbred dairy cows managed under various farm scales and farming systems in Southern and Oromia regional states. Multi-stage sampling technique was employed to select dairy farm households. The three districts was selected purposively based on the potential of dairy production system. A total of 120 households were selected randomly, 48 from Wondo Genet, 41 from Shashemene and 31 respondents from Hawassa districts.Data on the prevalence of RFM was collected mainly by two approaches: the first by monitoring smallholder and large scale dairy farms where total of 500 calvings had occurred between September, 2016 and May, 2019. The second form of data collection was by using secondary data from large scale dairy farms. The study was complimented by household survey, where the perceptions of farmers about risk factors and possible mitigation practices followed by farmers to prevent RFM. The result shows that out of the monitored calvings, 69 calvings (13.8%) had RFM. RFM progressively and significantly increased with the advancing age of the cow which is 9.2%, 14.4%, 15.4% and 15.3% respectively for. Parity of the cow was categorized as 1-2, 3-6 and >7. It was observed that 6.9%, 13% and 74.3% respectively. The prevalence of RFM in cows with poor, medium and good body condition is recorded as 18.6%, 4.3% and 66.7% out of positive cows respectively. The sex of delivered calf has its own impact on the prevalence of RFM where the incidence of RFM for female calves born was 10.7% and for male it was 17.5%. The incidence of RFM was also affected by blood levels of crossbred cows where 50%, 75% and 87.5% crossbred had 32.1%, 12.1% and 13.3% RFM prevalence, respectively. In conclusion, the prevalence of RFM in the present study area was so high, requiring special attention to be given, by considering important predisposing factors. In this study, the impacts of other important factors (such as effect of nutritional status of cows) were not considered, which might require further studies.