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.
CFD Calculation of Pressure Rise Due to Internal AC and DC Arcing in a Closed Container
Computational fluid dynamics calculation results of pressure rise and propagation due to high-current arcs in a closed container are described. The pressure developments at different locations within the container are calculated by changing the current frequency (ac of 50 and 60 Hz, and dc) and the electric arc energy input (up to approximately 1000 kJ). The local pressure oscillation amplitude for AC/50 Hz within the container exceeds that for dc. From the pressure oscillation period and the sound speed distribution in the container, the following conclusions are made. With growing electric arc energy, the pressure amplitude increases because of the resonance effect between the arc power oscillation and pressure waves reflected on the walls. When the electric arc energy reaches a value of around 500 kJ, the pressure amplitude rises significantly. This is considered attributable to superimposition of pressure waves near the container wall caused by low propagation velocity of the pressure waves near the wall. It is necessary to consider this phenomenon for public safety when designing electric power equipment.
Dynamics of a radiating gas with application to flow over a wavy wall.
The spherical-harmonic approximation developed in astrophysics and neutron-Iran sport theory is applied to the radiation-transport equation for a nonscattering, quasi-equilibrium, grey gas. To a first approximation, the exact multidimensional transport equation is replaced by four differential equations. The gasdynamic equations, together with the four approximate transport equations, constitute a determinate set of purely differential equations valid for the complete range of optical thickness. Boundary conditions consistent with such approximations are discussed. Within the framework of linearized theory, the governing equation and the boundary conditions on velocity and on the temperature jump at the wall are obtained in terms of a perturbation velocity potential. To illustrate the special features of two-dimensional flow with radiation, a solution is obtained for steady flow over a sinusoidal wall. The solution is valid throughout the ranges of temperature and optical thickness. It is found that two systems of waves are present, a modified classical wave and a radiationinduced wave. The occurrence of pressure drag at subsonic speeds and the smoothing of the transition from subsonic to supersonic speeds reflect the nonequilibrium character of the radiating-gas flow.