Field service evaluation of distribution fuse links

The real-world condition of one make and type of tin-element distribution fuse link after years of service on one system is explored to obtain a judgement regarding fuse-link deterioration as a cause for nuisance blowings. The microstructural analysis of all fuse links evidenced no structural changes typical of a fuse damaged by high-current pulse tests. The results of the melting current tests showed only 2% with a melting current reduction in time exceeding 10%. The occurrence of high rates of nuisance blowings reported on some systems may therefore be due to other causes or by the use of fuse types not studied. The authors postulate that recently published studies showing higher than expected magnetizing current inrush and transformer core saturation caused by low-current continuing lightning-current discharges may also account for nuisance fuse blowings. If so, the use of an ultraslow fuse link may be very effective