The performance of the vacuum interrupter determines the performance of the contactor, and the mechanical characteristics of the contactor itself also determine the performance of the vacuum interrupter. Whether the performance of a vacuum contactor meets the requirements mainly depends on whether its mechanical characteristics meet the requirements of the matching vacuum interrupter.
1, first look at the contact pressure. When there is no external force in the vacuum interrupter, the moving contact is closed with the static contact under the action of atmospheric pressure, which is called self-closing force. The magnitude of the force depends on the port cross-sectional area of the bellows, in general, the self-closing force can not ensure the qualified electrical contact between the dynamic and static contacts of the vacuum interrupter, and an external pressure needs to be superimposed. The magnitude of this pressure depends on three factors: a. the rated current of the interrupter, b. the material of the interrupter contacts, and c) the electrical repulsion between the static and dynamic contacts when the interrupter is closed. According to these factors, the appropriate applied pressure, the self-closing force and the superimposed external pressure are called the contact pressure of the contact, also known as the terminal pressure.
2, the role of terminal pressure on the contactor. Reasonable terminal pressure can ensure the qualified contact resistance between the dynamic and static contacts of the interrupter, and the contact resistance can be measured by the loop resistance tester; The reasonable terminal pressure can meet the requirements of the dynamic and thermal stability of the vacuum interrupter, and can overcome the repulsion between the contacts under the state of high current, so as to ensure that the contact is closed without damage, that is, the contacts will not stick to death; Reasonable terminal pressure can reduce the closing bounce, so that the impact force generated by the contact when it is closed is absorbed by the elastic potential energy; When the terminal pressure meets the requirements, the contact spring compression is also large, and the elastic potential energy is also large, which can increase the initial speed of opening when opening, reduce the arcing time and improve the opening capacity.
3. Definition and function of overtravel. Any vacuum switch is closed in overstroke mode, and when closed, the moving contacts cannot move forward after touching the static contacts, but pressure is required between the static and dynamic contacts. This pressure is realized by the contact spring, when the dynamic and static contacts collide, the force added to the contact spring will continue to move, and the displacement distance when continuing to move is the compression stroke of the contact spring, and this stroke is the overstroke. In addition to improving the initial speed of opening, over-stroke also has two important functions: a. over-travel makes the force produced by the contact spring be transmitted to the contact pressure between the contacts to meet the needs of operation; b. after long-term operation of the contactor, the dynamic and static contacts will be burned, which reduces the total thickness of the contact, and if there is a reasonable over-travel as a guarantee, a certain terminal pressure can still be guaranteed to make the vacuum contactor work normally. In fact, the contact pressure spring has given the compression amount of preload in the open state of the contactor, which is to make the moment of contact, reach the preload value to reduce the closing bounce, and when the overstroke movement is terminated, the terminal pressure also meets the design requirements.
4, the definition of closing time and opening time and the influence of the length of time on the performance of the switch.
a. Closing time: the time interval from the beginning of the closing operation to the moment of contact contact of the interrupter.
b. Opening time: the time interval from the beginning of the opening operation to the moment of separation between the contacts of the interrupter.
If the closing time is short, the closing speed will be fast, the arc caused by the pre-breakdown generated during the closing process will be small, the electrical corrosion on the contact surface will be small, and the service life of the arc extinguishing chamber will be long. Otherwise, there will be the opposite conclusion. However, if the closing time is too fast, it is easy to bounce, because the elastic potential energy of the contact spring has no time to absorb the sudden impact force, which will inevitably cause the bounce to increase. In addition, the closing time is too fast, the output power of the electromagnetic system is also large, and the mechanical impact on the interrupter and switch is also large, which will affect the reliability of the contactor. In this case, it is necessary to recalculate whether the matching degree between the mechanism and the arc extinguisher is appropriate.
In the same way, the opening time is short, and the opening speed is also fast. The opening speed is related to the size of the opening distance, and the speed of the opening speed affects the breaking quality of the interrupter. We know that when the current crosses zero, whether the breaking arc will be extinguished or not will be re-ignited mainly depends on the speed of recovery of the medium properties between the contacts, if the recovery time of the medium strength is greater than the speed of the recovery voltage rise, it will be re-ignited. Therefore, the opening speed is fast, which is beneficial to the breaking.
5. The influence of closing synchronicity on the contactor. The synchronicity of closing and opening are at the same time, so as long as the closing synchronicity is adjusted during assembly, the synchronicity of opening is also guaranteed. This is mainly determined by the assembly process, which is generally less than 2ms to meet the requirements. If the synchronicity is greater than 2ms, it is easy to cause closing bounce, because in the three-phase contact in the closing process, there is a first contact contact, and the impact energy when closing is also undertaken by the first contact, resulting in the phase bounce exceeding the standard.
