Analytical determination of the characteristics of enclosed and oil-immersed fuses

In a previous paper the authors dealt with the case of semi-enclosed fuses, manufactured from uniform thin strip or with single or double discontinuities in their cross-sections. An analytical solution for the time/current characteristic of such fuses was shown to exist, which was in very close correlation with experimental derivations of the same characteristics. This work has now been extended in two ways. First, the analytical derivation of fuse characteristic has been extended to cases of fuses with n discontinuities in their cross-sections, where n > 2; this work was carried out with the aim of investigating the full range of alternative characteristics available from such fuses. Secondly, and the most important part of the work, has been the extension of the solution obtained for a semi-enclosed fuse to fuses of similar metallic construction but immersed in oil or enclosed in a silica-type filler. Having established a method and form of solution, a substantial amount of computation is necessary in any one case; in order to facilitate computation, a simple form of transient analogue computer has been used, and is described in the paper. In the case of fuses immersed in oil or enclosed in silica-type filler, the main problems have been to establish the parameters of heat transfer prior to finding a form of solution of the relevant equations. The Appendices contain representative Tables of results in the form in which they were obtained from the analogue computer, and an analysis showing the feasibility of establishing a single series of Tables of analogue-computer results for fuses with multiple discontinuities in cross-section.