The Effect of Repeated Faults on Fuse Characteristics [includes discussion]

With the introduction of the automatic circuit recloser, it became necessary to consider the effects of a fault current repeated several times at short intervals upon the time current characteristics of a fuse link. The link goes through several sequences of heating and cooling, each application of the fault bringing a higher end temperature. This paper describes a study of the exact manner in which a fuse link behaves when such a series of repeated faults is impressed upon it. The temperature of the fuse link is traced as the fuse heats with the application of a fault, cools after the first interruption, and is brought to still higher temperatures by succeeding applications of the fault. In this manner it is possible to determine whether a fuse will blow or be damaged by a given sequence of repeated faults, or remain undamaged. Information also is presented for determining how co-ordination is affected by preloading and ambient temperature variations. A feature of this study is that damage to the link can be predicted for faults of insufficient duration to cause blowing. Equipment used for the tests is described.