Comparison of the properties of WCAg and WCCu as contact materials for vacuum contactors

WCAg has become one of the preferred contact materials in vacuum contactors for switching load currents of some hundred Amperes up to a few kiloamperes. It meets the requirements of vacuum contactors such as low erosion losses, low chopping currents, a sufficient quenching capability etc. Today´s efforts try to reduce the percentage of the expensive silver component in this material or to substitute it. In this contribution the effects of changing the percentages of Ag and WC as well as the substitution of Ag with Cu is discussed and the switching behavior described. The different materials are compared with respect to their breaking capability, their chopping current, their erosion losses and the state of their contact surfaces after arcing. The experiments were carried out with a demountable vacuum chamber in a synthetic test circuit. For the switching capability tests the contacts were stressed by arc currents up to 7 kA RMS and a transient recovery voltage of 23 kV peak. The chopping measurements were carried out at a test current of 45 A RMS in a test circuit with a resonant frequency of 6800 Hz and a surge impedance of 1066 Ohms.