Electrical contact materials play the role of conduction and isolation in AC contactors. Common electrical contact materials include silver alloy, copper alloy, etc. Silver alloy has good electrical conductivity and contact resistance stability, and is suitable for applications in low-current and low-voltage electrical appliances; copper alloy has high electrical conductivity and wear resistance, and is suitable for applications in medium-current and medium-voltage electrical appliances. Selecting the appropriate electrical contact material can ensure the normal operation and good electrical life of the AC contactor.
AC contactors are used in AC main circuits that are frequently connected and disconnected and need to have a high electrical life. This working characteristic requires high electrical wear resistance of its contacts. Since the connected breaking current is not high, the contacts need to have moderate welding resistance. Contactors with a rated operating current of less than 25A can use contact rivets; contactors with large operating current should use contact tips.
Small current level contactors (below 25A) have low requirements on the welding resistance of the contacts and use contact rivets. The contact has high production efficiency, and the contacts are directly riveted, which is convenient and fast. AgNi has good electrical conductivity and low and stable contact resistance. AgNi/Cu rivets are used in 10A contactors. AgCdO has good electrical conductivity and resistance to welding, and AgCdO/Cu rivets are used in 20A contactors. The environmentally friendly material AgSnO2 has higher resistance to welding and higher contact resistance. Using AgSnO2/Cu instead of AgCdO/Cu rivets has better welding resistance and electrical life of the contacts, but the contact resistance and temperature rise are relatively poor.
Contactors with high current levels require high welding resistance and current wear resistance of the contacts. The Ag-based contact tips made by the alloy internal oxidation method has good electrical conductivity and resistance to welding. Secondary dispersed oxide particles have high hardness and resistance to electrical wear. In addition to the advantages of high conductivity and high resistance to electrical wear of Ag metal oxide, AgCdO also has good arc extinguishing properties and stable contact resistance due to the presence of CdO. When a high-temperature arc (about 6000K) acts on the contact, CdO quickly decomposes, which can cool the arc, and the steam generated by sublimation can also lengthen the arc. The decomposition temperature of CdO is equivalent to the melting point of Ag. Its decomposition avoids liquid splashing and volatilization of Ag under the action of high-temperature arc. At the same time, an Ag-rich area is formed on the surface of the contact, making AgCdO have stable contact resistance. AgCdO contacts have the advantages of good electrical conductivity, electrical wear resistance, arc extinguishing properties and stable contact resistance. They are widely used in low-voltage electrical appliances and are called universal contact materials.
However, because AgCdO contains the harmful substance Cd, it does not meet the requirements of EU RoHS. At present, foreign developed countries have successfully produced a wide variety of AgSnO2 materials based on the use conditions of different electrical switches, using different metal oxides and through different processes, which have basically completely replaced AgCdO materials. However, domestic research on AgSnO2 contact materials started late, so there are still many problems especially in terms of electrical properties and processing properties of AgSnO2. With the deepening of research, our country's AgSnO2 contact materials will gradually replace AgCdO.
——The content of the article comes from the Internet