Contact Resistance and Arc-free Commutation Current of Tungsten-clad Copper Contacts for a Hybrid DC Switch

Hybrid DC switches have been intensively studied because of the increasing demand for DC power distribution systems. A hybrid switch consists of high-speed mechanical contacts, a power semiconductor device, and a metal-oxide varistor. The DC circuit current commutates from the contacts to the power semiconductor device, and is then interrupted by the power semiconductor device. Arc-free commutation is achieved provided that the contact voltage remains below the boiling voltage of the contact metal. Tungsten material is a suitable material for arc-free commutation; however, its higher contact resistance increases the contact voltage drop by Joule heating. Newly developed contacts that have tungsten-clad copper contacts exhibit the features of low contact resistance and high boiling temperature. The copper base material quickly removes the Joule heat from the tungsten cladding during the current commutation. The contact resistance was approximately equal to the value of copper, and the arc-free commutation-current increased from 120 to 400 A.