Recent developments in medium-voltage h.b.c. fuse links

The paper reports development work carried out in the investigation of fuse links of ratings up to 600 volts and 600 amp in respect of basic problems of design when compliance with North American specifications and general circuit requirements is sought. Although this work was of a fundamental nature for universal application, it was stimulated by the publication of the Canadian Standards Association Code 106. Comparisons are made between this Canadian Code, the `Standard for Fuses¿ used in the United States, and current practice in Britain, which centres on B.S. 88: 1952. Fundamental difficulties in fuse-link design are set out, leading to the choice of a design to satisfy general circuit requirements and the C.S.A. Code No. 106 in particular. Details of performance are given of the resulting range of fuse links. The results of the high-breaking-capacity tests carried out by the Canadian Standards Association are compared with the calculated figures. Consideration is given to consistency of performance, and tests to demonstrate non-deterioration under service conditions are described. A novel method is given for the rapid estimation of the effect of the fuse link in limiting fault power and energy admitted on severe fault conditions.