Internal arc fault simulation using CFD to predict thermal behavior in switchgear
During an event of internal arc fault in LV/MV switchgears an electrical energy of the order of several Mega-joules is released which should be dissipated in the span of few milliseconds. Major portion of this energy is utilized in the heating of the enclosure gases resulting in the significant pressure rise inside the chamber. Objective of the simulation model developed is to improve design efficiency, increased safety, and especially to minimise real-world testing. Internal arc parameters such as pressure rise in various compartment, exhaust gas temperature, indicator temperature and pressure on panel walls are investigated with CFD simulation methodology. A 3-D CFD simulation of high temperature gases in LV/MV panel is carried out with coupled interactions between flow, temperature, turbulence and radiation fields taken into account. The internal temperature and pressure rise due to internal arc at different locations in breaker, cable and busbar compartment were compared. The same is used further to analyse structural forces and stresses on the panel members. Temperature rise at different locations on indicator walls which are modelled at a distance of 300 mm from panel were estimated from simulation. Visualization of the temperature, pressure and flow field is possible with CFD model.
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 (kp), 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 kp. 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 kp agree with the experimental result within the error range.
Fragment Rotational State Distributions From The Dissociation Of NeIBr: Experimental And Theoretical Results
The IBr fragment rotational state distributions that result when the NeIBr van der Waals molecule undergoes vibrational predissociation have been measured in a pump–probe laser‐induced fluorescence experiment. Independent of initial vibrational state and the number of quanta of vibrational energy lost from the I–Br coordinate, the rotational distributions extend over the full range of energetically accessible states. From the observation of energetic constraints on the rotational distribution, the dissociation energy (D0) is calculated to be 65.5±1.2 cm−1 for the A electronic state, v=16. For the X electronic state, v=0, D0=71.8±1.2 cm−1. Quantum mechanical bound state calculations carried out on a model A electronic state potential energy surface are in quantitative agreement with this result. The rotational distributions are broader than that predicted by either a Franck–Condon or classical impulsive model for the dissociation. The distributions are qualitatively in accord with classical trajectory calc...