Relationship between Rated Contact Working Pressure and Breaking Short-circuit Current of VS1 Vacuum Circuit Breaker

With the development of social economy, our demand to electric power is increasing. The requirement for high-voltage breaking short-circuit current is increasing too. What is the pressure of rated breaking short-circuit current? Actually, the pressure is working pressure of contacts in a vacuum interrupter under the corresponding rated breaking short-circuit current. (This pressure is related to insulating rod)

The rated contact working pressure of vs1 vacuum circuit breaker is the sum of self-closing force of vacuum interrupter and closing spring’s force. Proper selection of working pressure of vs1 vacuum circuit breaker’s contacts can keep contact resistance of vacuum interrupter within a specified range. Within a certain range of contact pressure, the greater the pressure, the smaller the contact resistance. A small contact resistance can reduce the heat that generated by VCB during long-term operation, so as to ensure safe operation of VCB.

At the same time, sufficient contact working pressure can meet the requirements of dynamic stability test, withstand greater electric power, and can also inhibit closing bounce and reduce opening rebound. At making short-circuit current, the contacts of VS1 VCB will produce arc and electric repulsion after pre-breakdown. The contacts will bounce, and the mechanism’s closing speed is the slowest. Therefore, making short-circuit current is the toughest condition for checking whether working pressure of contacts meet the requirements.

If working pressure of contacts is too small, it will increase bounce time when contacts are closed, at the same time, cause resistance of primary circuit to increase, which directly affects long-term operating temperature rise of vs1 vacuum circuit breaker. If working pressure of contacts is too large, because self-closing force of a vacuum interrupter is a constant value, the working pressure increases, thereby increasing spring force of the contacts, causing closing power of operating mechanism to increase, and increasing shock and vibration, which will cause leakage in vacuum interrupter for a long time.

The empirical data of contact working pressure of vs1 vacuum circuit breaker is shown in Table 1 according to the rated short-circuit breaking current.