Experimental Investigation of Arc in Fuse Elements during the Interruption Process

Abstract

Electric fuses usually operate under either less than their nominal current or momentarily excessive or short-circuit currents. In the case of operation under excessive or heavy fault currents, the design of fuses is based on the principle that they must interrupt those currents in a very short time period [1–4]. In this case, an increase in the fuse element’s resistance causes the temperature to rise rapidly until the melting point is reached. The latent heat of fusion is produced gradually by the current during the melting process until the material is completely vaporized [1,4,5]. When the material of the element vaporizes, electrical arcs strike between the remaining solid parts of the element. This dynamic process gives rise to a rapid temperature increase, while the current decreases rapidly until its flow is interrupted [6,7]. The time period from the instant when the current exceeds the critical value until the melting and vaporization of the elements is taking place is known as the pre-arcing period and the following time until the arc interruption is achieved is called the arcing period. During the pre-arcing period the current varies with time in a way mainly determined by the source and the impendances in the circuit up to the point of fault. The fundamental operation of fuses has been described extensively, among others, by P.G. Newbery, A. Wright, E. Jacks, R. Rudenberg, D.R. Barrow and T. Chicata [1–7]. This research focuses on the arcing period. The fundamental operation is well understood in general, but not all of the physicochemical processes that occur during the arcing period seem to be completely understood.