Intelligent computer simulation tools for HV circuit breakers and issues related to simulation
Intelligent simulation tools are developed within the Integrated Simulation and Evaluation Environment using Visual Studio C++ and object oriented programming. Such an environment should result in huge savings in time and cost for switchgear manufacturers. Conventional k-epsilon turbulence model has been modified to take into account of steep radial temperature gradient at the arc edge with much improved results. Investigations of computational convergence and the effects of initial conditions show that solutions independent of initial arc conditions with sufficient accuracy can be achieved with the Liverpool arc model.
A comparative study of arc behaviour in an auto-expansion circuit breaker with different arc durations
A computational study of the thermal interruption performance of a 145 kV, 60 Hz auto-expansion circuit breaker has been carried out. The pressure peak in the expansion volume has a delay of 2.8–3.4 ms with reference to the current peak when the arc duration varies. A reasonable indicator of the interruption environment is the average mass flux in the main nozzle. The short arc duration case (12.25 ms) is the most difficult case with the lowest critical rate of rise of recovery voltage (RRRV) of 10 kV µs−1, just above the initial system applied RRRV of 9 kV µs−1. This is a result of an insufficient gas flow cross sectional area between the live contact and the main nozzle to develop rapid gas flow for arc cooling. The auxiliary nozzle plays two roles. It provides blockage in the high current phase to reduce gas exhaustion from the main nozzle into the hollow contact; after current zero the hollow contact shares a considerable portion of the system recovery voltage, especially for the short arc duration case (36%). Therefore the proper design and use of an auxiliary nozzle is key to enhancing the thermal interruption capability of high voltage auto-expansion circuit breakers.
Synthesis of β-FeSi2 nanowires by using silicon nanowire templates
Si nanowires templates were grown by a Cu-catalyzed vapor–liquid–solid process and used for the preparation of β-FeSi2 nanowires on a Si substrate. The silicon nanowires were transformed into β-FeSi2 nanowires by annealing with additional source material containing FeCl2 and Si powder. In contrast to uniform Si nanowire templates along the direction, the synthesized nanowires were deformed irregularly. The electron diffraction pattern of the nanowires synthesized from the template corresponded to that of single-crystalline β-FeSi2 and the longitudinal direction of the nanowire was along the direction. The energy dispersive X-ray fluorescence analysis confirmed that the nanowire contained Fe and Si in an atomic ratio of approximately 1:2. The results confirmed that β-FeSi2 nanowires on a Si substrate were synthesized from the Si nanowire templates.Si nanowires templates were grown by a Cu-catalyzed vapor–liquid–solid process and used for the preparation of β-FeSi2 nanowires on a Si substrate. The silicon nanowires were transformed into β-FeSi2 nanowires by annealing with additional source material containing FeCl2 and Si powder. In contrast to uniform Si nanowire templates along the direction, the synthesized nanowires were deformed irregularly. The electron diffraction pattern of the nanowires synthesized from the template corresponded to that of single-crystalline β-FeSi2 and the longitudinal direction of the nanowire was along the direction. The energy dispersive X-ray fluorescence analysis confirmed that the nanowire contained Fe and Si in an atomic ratio of approximately 1:2. The results confirmed that β-FeSi2 nanowires on a Si substrate were synthesized from the Si nanowire templates.