Thermal Analysis of the Fuse with Unequal Fuse Links Using Finite Element Method
In this paper a three dimensional thermal model of high breaking capacity fuse with unequal fuse links is proposed for both steady-state or transient conditions. The influence of ambient temperature and electric current on the temperature distribution inside the fuse, has been investigated. A thermal analysis of the unbalanced distribution of the electric current through the fuse elements and their influence on fuse link temperature rise, has been performed. To validate the three dimensional thermal model, some experimental tests have been done. There is a good correlation between experimental and simulation results. Keywords—Electric fuse, fuse links, temperature distribution, thermal analysis.
Numerical study of the short pre-arcing time in high breaking capacity fuses via an enthalpy formulation
In order to study the short pre-arcing time in high breaking capacity (HBC) fuses, we use a mathematical model including the phase change of the fuse-element heating coupled with the Laplace equation for the potential and Ohm's law. The thermal model is based on the enthalpy formulation of the heat equation with a source term representing the Joule heating. For the time range considered (up to 10 ms), we assume no heat transfer between the fuse-element and the surrounding sand. To solve numerically the governing equations, we employ a semi-implicit scheme for time integration and a finite element method for space discretization. Using electrical and thermal properties of the silver fuse-element, we present pre-arcing characteristics (temperature, current density, potential) for a fuse-element used in industrial protection circuits.
Pre-arcing behaviour of open fuse wire
A theoretical model of the pre-arcing behaviour of open fuse wire in air is presented. The model is based on the solution of the heat-transfer equation and accounts for axial thermal conduction, radial thermal radiation and free convection as the major heat-loss mechanisms, and Joule heating as the major heat source. The effect of thermal expansion of the wire is included. The results show that for short pre-arcing times, the heat loss from the fuse wire is negligible, but as fusing times increase, the radiation and free convection become the major heat-loss mechanisms. The theoretical results are compared with the measurements of the fusing time of copper fuse wires for currents ranging from severe fault conditions, with fusing times of the order of milliseconds, to low overcurrents with fusing times of the order of seconds. The transient and the steady-state temperatures for various currents obtained through the model are in good agreement with the measured values. The model is also used to compute the axial temperature distribution along the fuse wire. Finally, a sound agreement between the convection-loss values obtained through experiments on fuse wire in vacuum and air and those obtained through the empirical procedures used in the theory lends support to the validity of the latter.