Loss-Of-Excitation (LOE) condition of a generator may cause severe damages on both generator and the interconnected systems. This paper analyses the behaviours of different LOE protection schemes, such as R-X, G-B, P-Q and U-I schemes, for a hydro generator, which is connected to an infinite bus. Based on the simulation results, the reliability and stability of existing LOE protection schemes are compared and a preferred scheme is selected. An improvement to the scheme is also proposed to prevent the LOE relay incorrect operation during external faults, such as short-circuit faults on busbar or transmission lines.
The ballistic transport properties of Cu nanowires under different bending stresses are investigated for future application in flexible displays and flexible solar cell using first-principles density-function theory. The stability and quantum conduction of both nonhelical and helical atomic strands are reduced by applying a bending stress f. With increasing of f, the helical wire becomes disorder, suffering a phase transition to similar nonhelical one and collapsing eventually. Our calculations show that the maximum bearable bending stress is f max ¼ 3 nN for the helical atomic strands while is more stable than f max ¼ 2.5 nN for the nonhelical atomic strands.
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