Reliability concept for electric fuses

When fuses are subjected to current pulses, cyclic stress is induced owing to temperature variations. Damage in the fuse elements is gradually accumulated and results in resistance increase. Consequently, current-time characteristics shift to effect early operation during the normal service period. Under such circumstances, proper protection required for other equipment will not be achieved. Reliability concerns for after sales service arise owing to these facts. The paper presents a method for predicting lifetimes of fuses for cyclic loading. The physical model is based on the description of elastic, plastic and creep deformation during a series of current pulses. In comparison with existing methods and IEC recommendations, it has the advantage of requiring a very limited number of tests. Results from the physical model can be used to evaluate practical fuse designs and provide advanced information for fuse replacements. The method has been demonstrated for commercial time-lag miniature fuses, low-voltage fuses with M-effect, low-voltage fuses for semiconductor protection, and high-voltage fuses for motor protection