Topic/Type: 1.6 Plasma-based devices, Poster
D. Pavelescu1, S. Nitu1, G. Pavelescu2, P. Anghelita3
1 ?POLITEHNICA? University of Bucharest, Bucharest, ROMANIA
2 National Institute for Optoelectronics, Magurele, Bucharest , ROMANIA
3 Research and Development Institute for Electrical Industry, Bucharest, ROMANIA
The study is aimed to contribute to a better understanding of the complex phenomena that take place in the interruption process of high currents that appears in the short-circuit regime of electrical networks.
The vacuum circuit breakers produce a drown electric arc during the current interruption process. The contact separation creates a metal bridge that is melted, evaporated and ionized, becoming the initial form of the arc column. This initial form of the electric arc, observed for the small values of the gap, in spite of diffuse appearance, it is not extended over the entire electrode surface. During the high current evolution, when the current value exceeds 10kA, the arc column tends to concentrate and the arc forms an anode spot whose very high temperature produces an intense vaporization of the contact material. This process can further result in specific craters at the surface of the electrode. As a consequence the current interruption is severely impeded and the lifetime of the contact parts is reduced. A technical solution used to avoid such effects is the transverse magnetic field (TMF) technique. In the case of the TMF solution, the arc column becomes concentrated during the high current interruption process. In order to avoid its negative effects, the vacuum arc is rapidly moved over the contact surfaces. By a magnetically driven motion of the column the arc energy is homogeneously distributed over the contact surface, thus avoiding local overheating and facilitating the successful current interruption.
Mathematical models were used to describe the behaviour of the vacuum arc developed in circuit breakers in cup-shaped with cylindrical and spiral contacts in the presence of transversal magnetic field. Simulations of the magnetic field distribution and of the arc movement during the interruption process were obtained.