Transition boundary from metallic to gaseous phase in Pd break arc

Metallic-phase duration and transition ratio to gaseous phase were investigated for Pd contacts under the variation of closed contact current I_o, load inductance L (0.2-2.3 mH), and source voltage E (6-48 V). The results obtained were compared with results for Ag and W contacts, reported for the same circuit conditions. Experiments have revealed that the boundary closed contact current I_ob, at which the transition ratio is 50%, decreases with increase of L and E in the same manner as for Ag and W contacts. The metallic phase duration t _m was found to increase rapidly with I_o in the vicinity of I_ob, in a similar manner to Ag contacts. For Pd contacts, the degree of slope change of the t _m-I_o curve, at the point where the transition ratio attains about 100%, tends to be larger than that for W and smaller than that for Ag