The contact material (contact material) is an electrical contact material for switch, relay, electrical connection and electrical connector. It is also called electrical contact material. It is usually divided into two kinds of contact material and weak electric contact material.
In the switchgear, the electric contact directly bears the function of dividing and connecting the circuit and carrying the normal working current or carrying the overload current in a certain time. The key functions of all kinds of electrical appliances, such as the interruption ability of the distribution electrical apparatus, the electrical life of the electrical apparatus and the reliability of the relay, are all dependent on the working performance of the contact and the performance of the contact. Quality. At the same time, the contact is also the weakest link in the switch and the part of the fault easily. If the contact system can not work normally, such as the short circuit of the power system, the contact of the high voltage circuit breaker refuses to disconnect, which will cause extremely serious consequences.
For detachable electrical contact elements, the working condition of the current in the closed contact state is similar to that of the fixed contact electrical contact. In this case, the main function of the electrical contact is to carry the current, the power transmission and the signal transmission. This requires a low and stable resistance. Because the Joule heat effect of the contact resistance is serious, it will cause the material to melt in the spot area of the contact and cause the electric contact to weld together, causing the so-called "soldering" phenomenon. When the welding force exceeds the mechanical breaking force of the switch, the contact can not be disconnected and the breaking circuit fails, even if it is not. Such a phenomenon which can not be disconnected will also delay the breaking operation of switching devices.
The value added mechanism of contact resistance in the switch electrical apparatus is different from that of the contact resistance of electric contact material in the field of weak electricity. In addition to various environmental stresses, such as oxidation, vulcanization and adsorption, there are arc discharge effects between the contacts (electrodes) in the process of breaking and connecting the circuit. Contact resistance increases due to erosion and transfer of contact materials, phase transition of materials and chemical reactions at high temperatures. At the same time, it will aggravate the effect of some environmental stresses. Of course, in this process, the high temperature of the arc will also destroy some thin films on the contact surface.
The split circuit is another main function of the switchgear, which also makes the problem more difficult because of the electric arc discharge between the contacts when the electric contact is directly borne and broken. When electric arc discharge is discharged, the contact has not only the effect of heat but also the effect of force, and the complex physical and chemical processes on the contact surface, such as material change, material erosion, material transfer and metallurgy process in molten pool. These processes are closely related to the arc characteristics determined by electrical conditions, and are closely related to the composition and characteristics of contact materials themselves and even to the manufacturing technology.
The connecting circuit is also one of the important functions of the electric contact. In addition to the short arc discharge of the gap gas breakdown during the contact closure, the main problem is the mechanical shock of the static contact or the dynamic contact caused by the mechanical shock of the electric contact mechanism, especially the inductive circuit, when the contact is closed. A larger impact current will result in the continuous and multiple effects of the arc discharge on the electrode in a short time, forming a so-called "fusing welding". Generally, the amount of molten metal increases with the drop of melting point and thermal conductivity.
Therefore, not only the different electrical contact forms require different electrical contact materials, but even the same type of electrical contact, such as the detachable contact material, must have different characteristics when it performs the different functions. In any operation of electrical contact, the phenomena often overlap each other, so the relationship between the various phenomena must be considered, which is the difficulty in the research of electrical contact theory and the development of new electrical contact materials.