การวิเคราะห์ความเสียหายของก้านเหวี่ยงในอุปกรณ์ตัดต่อวงจรเครื่องกำเนิดไฟฟ้าที่โรงไฟฟ้าเขื่อนสิริกิติ์

Abstract

In this research, the main causes of the damage of the lever arm in the generator circuit breaker at Sirikit Hydro Power Plant had been successfully analyzed. The method to prevent the damage had been also proposed. While the electrical circuit is opening, the lever arm rotated at high speed and then stopped by the impact adsorption equipment. Thus, the lever arm could be damaged, if the impact adsorption equipment does not function properly. Besides the impact cause, it also depends on the strength of the material. Herein, the impact intensity of the lever arm and the strength of the material were investigated using the collected velocity profile data of the lever arm, chemical composition analysis, and physical and mechanical properties of the lever arm. With respect to the above data, the simulated movement and impact were also demonstrated based on the Finite Element Analysis (FEA). Regarding the results, e.g. the stress distribution of the lever arm, the consistency between the actual damage and simulation result was studied. The lever arm was made from the A356 aluminum alloy casting, which was indicated as the dendrite structure. The shrinkage porosity, which was observed via SEM technique, was a significant effect on the lower mechanical properties of the lever arm leading to reduce the tensile strength and elongation due to tensile properties as well as lower impact energy absorption. The fracture analysis on the surface of the lever arm indicated the cleavage and dimple. Regarding the FEA simulation, the pin holes were determined as the critical area, which was the same as the actual damage on the lever arm. With respect to the results, the defectiveness of the materials is the main cause of the failure of the lever arm. Thus, material mechanical properties certification from the manufacturer is highly essential. The deficiency of the spare parts could be achieved by CNC machining the spare lever arm that made of aluminum materials, which should be high toughness and strength materials to prevent fracture damage. To reduce the chance of a serious collision, the parts of the circuit breaker mechanism must not be jammed during the process. Moreover, the regular operation and maintenance of the dashpot mechanism would also be highly necessary.