Experimental and theoretical study of internal fault arc in a closed container

The characteristics of an internal fault arc in an air closed cylindrical container have been investigated both experimentally and theoretically. Arc voltage, arc current as well as pressure variations at two different locations within the container are measured for electrode gap lengths of 10, 30 and 50 mm with peak current ranging from 1 to 20 kA of direct current (dc). The fraction of electric arc energy leading to pressure rise in the fault arc, which is known as the thermal transfer coefficient (k_p), is also obtained according to the experimental data. The arc motion is recorded during the whole arcing by high-speed camera. The radiation intensities of the spectral lines at wavelengths of 510.64 and 515.39 nm of the Cu atom originated from the copper electrodes are detected by spectrometer, from which the arc temperature is obtained by means of the two-line method. A two-dimensional axisymmetric cylindrical coordinate model for fault arc is developed based on magneto-hydrodynamic (MHD) theory with coupled interactions among the flow, temperature, electromagnetic, turbulence and radiation fields taken into account, which simulates the distributions of temperature, pressure, arc voltage as well as k_p. Particularly the internal pressure rise and propagation due to fault arc at different locations within the container are analysed. The results show that radiation and turbulence are two key energy transfer mechanisms in modelling the fault arc. Compared with the net emission coefficient radiation model, the P1 model is more suitable to calculate the pressure variation in fault arcs with the re-absorption effect contributing to the pressure rise considered. The computed pressure variation, arc temperature, arc voltage and k_p agree with the experimental result within the error range. (paper)