At present, vacuum switches have been widely used in various fields at home and abroad. With the popularization and wider application of vacuum switches, users are increasingly in urgent need of understanding and mastering knowledge related to their principles, structures, operation, and maintenance. Based on practical experience, this paper theoretically analyzes the selection principles and empirical data of mechanical parameters for outdoor high-voltage vacuum circuit breakers, aiming to provide technical references for users to better use vacuum switches.
1. Contact Operating Pressure
The contact operating pressure of outdoor high-voltage vacuum circuit breakers has a significant impact on their performance, and this pressure is equal to the sum of the self-closing force of the vacuum interrupter and the contact spring force. The selection of the contact operating pressure for circuit breakers must meet four requirements: a) Maintain the contact resistance of the vacuum interrupter within the specified range; b) Satisfy the requirements of the dynamic stability test; c) Suppress closing bounce; d) Reduce opening vibration. When an outdoor high-voltage vacuum circuit breaker closes a short-circuit current, arcing and electric repulsion will occur after the pre-breakdown of the contacts, leading to contact bounce, and the closing speed of the mechanism is also the slowest. Therefore, closing short-circuit current is the most severe condition to verify whether the contact operating pressure meets the requirements.
2. Opening Speed
Since the opening speed directly affects the recovery rate of the dielectric strength between contacts after the current crosses zero, if the recovery rate of the dielectric strength between contacts is less than the recovery voltage after the arc is extinguished, arc reignition will occur. To prevent arc reignition and shorten the arcing time, the opening speed must meet specific requirements. The magnitude of the opening speed mainly depends on the rated voltage. When the rated voltage and contact opening distance are fixed, the fluctuation range of the opening speed is determined by factors such as the breaking current, load characteristics, and recovery voltage. When the breaking current is large, the opening speed should also be large. When breaking capacitive current, due to the high recovery voltage, the opening speed should be increased to reduce the probability of reignition. The opening speed of 10kV vacuum switches is usually set at 0.8-1.2m/s, and can be higher than 1.5m/s if necessary.
This paper is compiled and organized by DAYA Electrical Group Co., Ltd. (https://www.hygraphics.com/). Reproduction is permitted with proper attribution.