The long-time operation of the modern high rupturing capacity fuse using notched strip elements and M-effect alloy, is governed by the inter-relationship between the element current distribution, the corresponding element temperature distribution, and the M-effect diffusion rate. This thesis describes a novel method which has been developed to model these complex effects, and hence determine fuse-link pre-arcing behaviour. The method is based on modelling both temperature and diffusion as electrical analogues and to utilise a computer circuit analysis software package to simulate the resulting circuitry. Although such packages have been available for several years, they have never been used, as far as it is known, to model fuse operation. The model enables fuse parameters to be studied to depths previously not possible, and offers unrivaled possibilities in the fields of fuse design and fuse applications. Examples of temperature distribution and diffused element concentrations and their variation with both current and time are shown, and comparisons of calculated and experimental results given. The cooling effect of the granular filler and its variation with filler depths is also studied. The data for the diffusion model is obtained from fuse elements which have been heat treated under both constant temperature and constant current conditions and then extensively analysed using both optical and scanning electron microscope, S.E.M., techniques. Measurements from the micrographs obtained enable both the diffusion coefficient and activation energy of the system to be determined. The effects of varying the quantity and composition of the M-effect alloy and their impact on fuse operation are also presented. The model is used to predict the time-current characteristic for fuse elements both with and without M-effect and comparisons with experimental data made. Finally, the possible ageing of fuses utilizing M-effect is studied and fuse service-life predictions made.
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