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.

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Numerical study of the short pre-arcing time in high breaking capacity fuses via an enthalpy formulation

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.

https://iopscience.iop.org/article/10.1088/0022-3727/20/10/005/pdf

Pre-arcing behaviour of open fuse wire

In this paper, we present a model and a numerical method of the fuse element heating including solid-liquid-vapour phase transitions in order to evaluate the pre-arcing time in HBC fuses The mathematical model is based on the enthalpy formulation of the heat equation with a source term representing the Joule effect coupled with the Laplace equation for the potential and the Ohm's law We obtain an approximation of the governing equations using a specific numerical scheme for time discretization and unstructured triangle or tetrahedral element grids are employed in spatial discretization using a standard piecewise linear finite element method Numerical simulations of two fuse elements, used in industrial applications, are carried out and compared with experimental measurements obtained using a 100 kVA power station

Modelling of the pre-arcing period in HBC fuses including solid - liquid - vapour phase changes of the fuse element

The heating of notched fuse elements under a.c. short-circuit conditions has been studied, using finite-difference methods to solve for the transient current and temperature distributions in the element. The method gave good agreement with experimental results. A comparison of the behaviour with that of a uniform-section element described in a companion paper shows that there are significant differences. In particular, the notched element shows large discontinuities in the time/current characteristic, and a wide variation in prearcing I2t, depending on the circuit parameters.

A.C. short-circuit performance of notched fuse elements

A new experimental set-up has been designed to observe spectral studies in fuse arcs. The fuses studied here are high breaking capacity fuses. They consist of a fuse element (in silver or copper) surrounded by silica sand. In this study, the arc dissipates 1200 J, the peak of electric current is about 2000 A and the duration of the arc is 3 ms. The maximum cross section of the squeezed arc is about 0.5 mm * 5 mm. The whole of the visible spectrum has been registered, from 360 nm to 800 nm, in the exploding part of the arc. The spectrum consists of continuous light together with spectral lines. The continuous light intensity is closely correlated with current intensity. The spectral lines appear mostly when the current decreases. The behaviour of the spectra shows that there is a big gradient of species concentrations in tha arc, together with a high grandient of temperature. The temperature is measured from Si II lines in the arc core. The calculation gives about 30 000 K at 1.3 ms. The measured values of electronic densities vary between 10E17 and 10E18 per cm3

http://iopscience.iop.org/article/10.1088/0022-3727/32/14/322/pdf

Measurements of time-resolved spectra of fuse arcs using a new experimental arrangement

The complex nature of heat flow within a modern current-limiting fuselink precludes direct analysis using classical techniques. This paper describes a method which has been developed for determining the prearcing and steady-state behaviour of such devices. It uses a finite difference technique and is numerical, the calculations being performed by a digital computer. Examples of current and temperature distributions found for some fuse-links are given, and comparisons of calculated and test results for fuselink-clearance times are shown.

J.G. Leach

Papers

Analysis of high-rupturing-capacity fuselink prearcing phenomena by a finite-difference method