Intelligent fuse-saving

Fuse-saving practices have coordination limitations at higher current levels — it is common for the upline device to trip and the fuse to operate at the same time. The result is frequent momentary outages for many customers and blown fuses, even for temporary faults. These challenges have led some utilities to abandon the practice of fuse-saving and instead migrate to a fuse-blowing philosophy. The conventional fuse-saving practice has an inherent tradeoff of sustained outage improvement at the expense of increased momentary activity. Ratings under the reliability indices SAIFI and SAIDI are improved, but the gains are offset by an increase in momentary events, reported as MAIFIE. When the fuse blowing practice is employed, the tradeoff is reversed — reduced momentary activity comes at the expense of more frequent sustained outages. The new fuse-saving philosophy described in this paper offers several improvements over conventional practices by extending the range of coordination, minimizing miscoordination with downline devices, and eliminating unnecessary tripping. An optimized composite phase and ground fuse-saving TCC curve is developed for the smallest downline fuse that is to be saved. Tripping on this curve only occurs when it can actually clear the fault before the fuse begins to melt. If the fuse cannot be saved, the initial tripping operation of the upline device shifts to a more delayed curve to allows the fuse to operate. While most utilities use a mix of fuse-blowing and fuse-saving on different feeders, this new fuse-saving philosophy achieves an intelligent mix of both practices on the same device.