Vacuum circuit breakers, without exception, adopt a docking contact method. After the moving contact touches the stationary contact, it cannot move forward anymore. The contact pressure is provided by the compression spring (sometimes called closing buffer spring) of each pole contact. The so-called contact stroke refers to the distance that the contact spring continues to move until the end of the contact contact contact contact, i.e. the compression distance of the contact spring. Therefore, it is also known as the compression stroke.
The contact stroke has two functions: firstly, it compresses the contact spring and provides contact pressure to the mating contact; The second is to ensure that a certain contact pressure is maintained even after wear and tear during operation, ensuring reliable contact. The general contact stroke can be about 20% to 30% of the opening distance, and the vacuum circuit breaker for 10kV is about 3-4mm. [3]
In the actual structure of a vacuum circuit breaker, the contact closing spring is designed to have a considerable pre compression force even when in the open position. This is to ensure that during the closing process, when the moving contact has not yet touched the stationary contact and pre breakdown occurs, the moving contact has a considerable force to resist the electric force and will not retreat backwards; At the moment of contact, the contact pressure suddenly increases to the pre pressure value to prevent closing bounce, which is sufficient to resist electric repulsion and ensure a good initial state of contact; As the contact stroke progresses, the contact pressure between the contacts gradually increases, and at the end of the contact stroke, the contact pressure reaches the design value. The contact stroke does not include the pre compression range of the closing spring, it is actually the second compression stroke of the closing spring.
