Commutation and Erosion in Hybrid Contactor Systems

Basic investigations of the commutation and switching mechanisms between contacts and parallel thyristors and on results of erosion measurements at currents up to 500 A, 220 V, 50 Hz are reported. The experiments are carried out with different contact materials (copper, hard silver, silver/metal oxide compound). Depending on thyristor data; commutation inductance, contact material, and current, the commutation time and thus the arcing time for a given arrangement lies in the order of tens of microseconds. Consequently the contact erosion stays low. In comparison with conventional contactors the material losses are two to three orders of magnitude lower. Different contact materials range qualitatively in the same sequence as in conventional switches. The arc voltage at and immediately after the contact separation is analyzed. A simple model taking into account the current constriction in the contact material near the arc roots can explain the measured dependences.