Application Of Contact Materials In Low-Voltage Apparatus

As a key link in power system, low-voltage apparatus works for the transmission of electricity to the consumer. It adjusts the working status of the load by electricity distribution, distribution circuit protection and control between load and low-voltage side of transformer, such as Air Circuit Breaker, Molded Case Circuit Breaker, Miniature Circuit Breaker and AC Contactor. Low-voltage apparatus consists of contacting system, sensing system, mechanical drive system and so on. Therefore, contacting system plays an important role, while contact is the key to this system. In light of this, high performance is required for the contact material. For example, favorable electrical conductivity and thermal conductivity, well resistant to electric fusion, difficult for arc resistance during large-current break, electrical wear resistance, low carrier level, low gas content, high chemical durability, organic contamination resistant, well machining property and welding ability. Silver, which plays the role as matrix of contact material, is a good conductor of electricity. However, this metal performs weak resistance of adhesion and electrical wear, in which refractory metals or metallic oxide should be added. There are several contact materials, including silver, silver nickel, silver cadmium oxide, silver tungsten, silver graphite, silver tungsten carbide graphite. Otherwise, techniques as induction melting, powder metallurgy, metallic internal oxidation, powder plastic deformation and infiltration-sintering technology were employed for contact preparing.Generally speaking, different low-voltage apparatus requires different contact materials, and furthermore, every kind of contact needs corresponding preparation procedure. It seems more economical, more environment-friendly and more optimal designed to choose proper contact materials and preparation procedure. In this thesis, the author analyzed the difference of preparation procedure for contact, studied the diversity of property between contact materials, and discuss the functional requirement of electronic equipment. The research content can be divided into three parts as follows.1. Application of contact materials in AC Contactor. Under low current (below25A), since it requires only low adhesive resistance, rivet contact should meet the requirement. While under large current (25A-630A), Ag-matrix sheet contact prepared by metallic internal oxidation can be used because of high adhesive resistance and electrical wear resistance. 2. Application of contact materials in Miniature Circuit Breaker. Miniature Circuit Breaker is mainly used in low voltage final power distribution of residential houses and buildings. It requires high security due to the purpose of short-circuit protection. AgC sheet contact, with favorable electrical conductivity and welding resistance, seems to be a good choice.3. Application of contact materials in Molded Case Circuit Breaker. Molded Case Circuit Breaker is mainly used for short-circuit current breaking, which requires adhesive resistance and arc resistance. In this part, employment of asymmetrical contact matching was studied, including a active contact with well arc resistance and a inactive contact with high adhesive resistance.