Type of contact
With the development of high voltage, high current, miniaturization and long life of switching devices, the electrical properties of contact materials are required to be higher and higher. Nanometer contact materials have become a hot spot in the research and preparation of contact materials.
The material property of contact is one of the key factors affecting the working characteristics and electrical life of vacuum switchgear. Almost all early vacuum switches used tungsten, molybdenum and other refractory pure metals as contact materials. This contact material has a series of advantages, such as appropriate breaking performance, good compressive strength and welding resistance, appropriate thermal conductivity and conductivity, low ablation rate during arc combustion, long contact life, etc. It is widely used in breaking small current vacuum switch. However, high melting point pure metal contact materials have many shortcomings, such as breaking current and high cut-off level, which limit the application range of vacuum switches.
The standard diode greatly extends the return time, and the connection of ordinary diode and zener diode has little effect on the return time. For inductive load, when the contact is separated, the arc generation time will be prolonged and the contact life will be shortened. For example, a relay with a diode connected to a coil takes 9.8 milliseconds to release the contacts. If the Zener diode is combined with the small signal diode, the time will be shortened to 1.9 milliseconds. The return time of the relay with no diode connected to the coil is 1.5 ms. When the service life of the relay approaches the later period, the contact resistance increases rapidly. At normal room temperature and pressure, the core dielectric breakdown voltage of air is 2