High voltage dc relay, originally, it was mainly used in power industry, aviation and aerospace industry. In recent years, electric vehicles have gradually emerged and driven distribution system has become a very important application market of high voltage DC contactor. High voltage is relative to low voltage system of 24V, 48V. Some low-speed electric vehicles choose 60V and 72V system power configuration, generally, the voltage of high-speed passenger cars is more than 200V, and the bus can reach more than 600V. Meet the requirements of this voltage phase are called high voltage DC relays.
High voltage dc relay includes mechanical life and electrical life two parameters. The influencing factors of mechanical life include contact material, design and manufacturing level. The bottleneck of electrical life is mainly in the contact life.
1.Influence of magnetic field arc blowing on electrical life of contact
Magnetic blowing is the use of permanent magnets or electromagnets to produce a magnetic field, The direction in which the magnetic field interacts with the arc is to pull the circuit away from the dynamic and static contact
With the rapid movement of the moving contact and the application of magnetic blowing effect, the arc is stretched, and the arc resistance increases rapidly, the arc current drops sharply and the thermal efficiency of the arc decreases accordingly, the conductivity of arc channels decreases. If the arc is drawn at the same time, in the process of arc outward movement, cooperate with other means of cutting arc and cooling arc, the arc will be extinguished more quickly.
Reducing arc time is an important means to protect contact. A good magnetic blowing design can prolong the life of the relay. Magnetic blowing has been widely used in high-power relays and contactors that are not sensitive to space requirements. In small relays, only individual products have designed similar devices.
2.Influence of ambient air pressure on electrical life of contact
In order to shorten the arc burning time, in addition to using the above magnetic blowing means to pull the arc, the method commonly used for arc extinguishing in a narrow space is fill the sealed arc extinguishing chamber with high ionization energy gas or vacuum the arc extinguishing chamber.
3.Influence of mechanical parameters on electrical life of contact
The structural parameters related to the electrical life of the contact include: contact area, breaking mechanism, contact pressure, etc. The contact area, the larger contact area of the dynamic and static contact, can provide a larger path for the current, reduce the contact resistance and reduce the temperature. When the relay is closed or broken, the heat generated by small arc ignition will be more easily released as the contact is larger, thus reducing the risk of contact melting.
Breaking mechanism is another key technology in relay design. The mechanism itself has a stable operation cycle, and the time required from starting to final movement to the maximum position of open distance directly affects the arc burning time.
The contact pressure of moving contact and static contact, There is always contact resistance between moving and static contacts. The greater the contact pressure, the smaller the resistance, It can reduce the electrical loss and temperature rise under the normal working state of relay.
4.Sealing property of arc extinguishing chamber
The vacuum arc extinguishing chamber is impossible to achieve the absolute seal, and there is the possibility of air leakage in the shell welding seam and so on. The design index has included an allowable leakage coefficient, and chronic leakage is inevitable. In addition, relays in electric vehicles in the violent vibration environment also have a serious test of the quality of sealing. As more and more air enters into the sealing chamber and the sealing property of the shell becomes worse and worse, the vacuum degree in the arc extinguishing room gradually decreases and the arc extinguishing ability also gradually becomes worse, which is an important factor affecting the life of the relay.