Experimental Investigation of the Influence of Different Magnetic Field Alignments on the DC Arc

The changing grid structures of DC grids are placing new demands on switching devices, particularly on their switch-off speed. For these reasons, the switching behavior of electromechanical switching devices was investigated with the goal to rapidly extinguish the arc. This can be achieved by rapid commutation of the arc onto the rails and into the arc chamber. Commutation in the electromechanical switching device can be facilitated by using radial or axial magnetic fields. Experiments were conducted utilizing a model switch with Helmholtz coils to generate the different external magnetic fields. Switch-off tests were carried out on the model switch at a voltage of 230 V (DC) and currents of 16 to 320 A. Contacts made of Ag/Ni 90/10 and Ag/SnO2 88/12 were used. The arrangement of the Helmholtz coils allowed a radial magnetic field (RMF), an axial magnetic field (AMF) or a combination of both (XMF) to be generated. The magnetic field of the coil arrangement was varied between magnetic flux densities of 10, 25 and 40 mT. The commutation time of the arc on the rails and the erosion of the contacts was investigated. High-speed recordings were made during individual tests. The distribution of the magnetic flux density in the switching chamber was also analyzed with simulations carried out in COMSOL. The combination of the results from simulation and tests led to a more precise understanding of the influences of the magnetic fields on the arc.