About relay, contactor, electrical contact and contact
About relays, contactors, electrical contacts and contacts. I believe all electricians are familiar with electromagnetic relays and contactors. The knowledge about these two kinds of electrical equipment has long been shared by many peers. Today, the author only supplements the contact knowledge of electromagnetic relay and contactor.
The contact burning failure of electromagnetic relay and contactor is a problem we often encounter in our work. The reason for this situation is nothing more than two possibilities: first, the load current flowing through the contact is relatively large, very close to the rated value. Although it does not exceed the rated value of the contact, it is easy to burn the contact after long-term use; In addition, for the above two kinds of electrical equipment, especially the contactor, most of their loads are inductive loads. Although the load current is small, when the contacts are disconnected and released, they are easily damaged by the arc released by the inductive load. As far as electromagnetic relay and contactor contact are concerned, series and parallel connection are very popular in some practical applications. In some electrical circuits requiring interlocking and interlocking control, if a single contact of relay or contactor is used, the relay and contactor may act too fast, which will cause the circuit unable to complete the action state switching. At this time, we can eliminate this phenomenon by connecting two or more contacts of relay and contactor in series, and by increasing the action distance of contacts - extending the action switching time accordingly.
Similarly, it can be known that when the contact capacity of relay and contactor is damaged due to large load current, it can be overcome by expanding the contact in parallel. In a word, the causes of contact burning of electromagnetic relay and contactor are relatively centralized and easy to solve. In the electrical control circuit, we can flexibly use contact wire and parallel connection to solve some practical problems.
Disconnectable contacts are an indispensable part of switching appliances. According to their different structures, they can be divided into the following types: (1) Knife contact: it has a simple structure and can be divided into surface contact and line contact, which are widely used in low-voltage switches and high-voltage disconnectors. (2) Butt joint contact: It has the characteristics of simple structure and fast action, but the contact surface is unstable and varies greatly with the pressure. It is easy to rebound during operation, without self-cleaning effect, and the contact is easy to be burned by electric arc. This contact is usually used for distribution circuit breakers with rated currents below 1000 A and below 500 A
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.