Sticking trouble rate on Cd‐added Ag‐based contacts

Abstract

Because the Ag‐oxide dispersed alloy‐type Ag/CdO electrical contact is supposed to have superior welding resistance, this type of contact has been used for circuit breakers designed for medium current. However, there has been no report made on the comparison between the sticking characteristics of Ag/CdO and Ag/Cd contact members. Contact members made of Ag, Ag/CdO 12 wt% and Ag/Cd 11 wt% were mounted in relays with a breaking force of 15 gf, and the ratio of sticking problems in each contact member was investigated during make‐and‐break operations of a dc 30V‐3Q resistive circuit. When the breakers were used for the make‐and‐break or break‐only operation, there was almost no sticking problem, regardless of contact material type. However, when the Ag/Cd contacts were used for make‐only operation, the sticking problem occurred in as much as 50 percent of the cases. When the Ag/CdO contacts were used for the make‐only operation, it was as high as 90 percent. When the Ag/Cd and Ag/CdO contact members were used for make‐only operation, a large pip and crater were observed on the surfaces of the electrode pairs. In addition to the experimental results described here, when the contact sticking occurred, the difference in the contact resistance values before and after the make‐only operation was evaluated. The main cause of the sticking problem was believed to be the locking between the pip and crater on the surfaces of the contact electrodes.

Fabrication and Arc Erosion Behavior of Ag-SnO2-ZnO Electrical Contact Materials

“…% CdO), have been the preferred material for electrical contacts applications for many years [ 1 ] thanks to their high electrical and thermal conductivities [ 2 , 3 ], high resistance to arcing [ 3 , 4 , 5 ], high welding adhesion resistance [ 6 , 7 ], low contact resistance [ 6 ], hardness and strength [ 2 , 3 ]. Nevertheless, given the toxic nature of Cd and its compounds [ 7 , 8 , 9 ], the use of this element is expected to be minimized shortly. In this context, Directive 2011/65/EU of the European Parliament (RoHS 2011/65/EU) has restricted the use of Cd in electrical and electronic equipment.…”