Pre-arcing stage is the first working step in high breaking capacity (HBC) fuse operation and affects the following step, namely, the arcing step. We have performed realistic HBC fuse tests for short (<10 ms) and medium (>10 ms) pre-arcing times by varying the phase angle of the electrical fault (defined as the phase angle of the fault current once the supplied voltage is applied to the fuse) in the range from 0° to 160°, for two values of the power factor (cosφ ∼ 0.9 and cosφ ∼ 0.1). Experimental values of the pre-arcing time and the arcing time (tarc) are given for tprearc/tarc ≲ 1 to ∼4.2, and discussed from the energetic point of view by taking into account the inductive source term. The adiabatic assumption classically used in the modelling is also examined. The influence of the pre-arcing step on the arcing step is analysed by means of the Joule integral, the energy dissipated in the fuse and the mass and length of the fulgurite.
The evolution of a low-voltage electric arc is studied with a matrix of microcoils which behaves like a magnetic camera. The arc is assimilated to a series of straight segments. The shape that it assumes in the electrode gap as well as re-striking phenomena are analysed. The influence of insulating and conducting obstacles is stressed.
A better knowledge of the electric breaking-arc car be obtained through electrical, optical and magnetic diagnoses. Therefore, a system called a 'magnetic camera' has been devised and developed. It consists of a V-shaped matrix, with some 70 probes, each of which gives the shape of magnetic Induction versus time in the gap between two electrodes. The various shapes assumed by the arc can be determined by means of data-acquisition and processing software within a few minutes. This type of camera is characterized by a maximum speed of exposure which is five times faster than that of an ultra-high-speed optical camera. Moreover, the diagnosis obtained is closer to the baslcally electric nature of the arc. Flgure 5. Acquisition system.
The evolution of an inverse diagnostic method used to study a low-voltage arc breaker is presented. The treatment of induction measurements obtained outside the arc breaking set-up allows us to reconstitute the arc dynamic. The arc is simulated as a multi-linear thread-like line sliding between two parallel rails. We used this method in order to study the behaviour of the arc for arc-breaking chambers composed of several materials and for various intensities of the current. We also calculated the values of , where is the arc conductivity and S is its cross section and, in some cases, we evaluated the values of the arc cross section.
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