Research On Relationship Between Interrupter Vacuum Degree And Shield Electric Potential

Vacuum circuit breaker(VCB) is a kind of power switch which takes vacuum ambient as the arc extinguishing medium, and it has been widely used in transmission and distribution systems. Vacuum interrupter is the core component of VCB, and it is responsible for arc extinguishing whose key factor is the internal vacuum environment. With the passage of working time, however, the internal vacuum of interrupter will declined gradually, and arc extinction will be failed and may bring security risks when it drops to a certain extent. Therefore, interrupter vacuum testing must be carried out to ensure the reliability and safety. The vacuum testing methods of vacuum interrupter can be classified into off-line testing and on-line testing, and the latter one, with the merits of good real-time performance, less maintenance, compact structure and so on, is regarded as the future trend. The shield potential based method is a main one of on-line testing, but it still in the exploration stage in high-precision and practical direction.Further exploration and research on the relationship between vacuum degree and electric potential of interrupter was carried out in this dissertation. Firstly, the relationship between gas pressure and its relative permittivity was built with the combination of Clausius-Mossotti equation and ideal gas-state equation, and based on this, electrostatic field analyses of vacuum interrupter under various pressure state were carried out in the finite element analysis tool ANSYS. The analyses results show that the changes of shield potential under different pressure can be reflected by measuring the potential of interrupter external measurement point. In addition, the measurement point potential begins to have more obvious change when the internal pressure reaches to 10-2Pa. In addition, to validate these results and provide experimental basis for follow-up studies, vacuum simulation testing system was established. This system consist of vacuum system, vacuum regulating and measurement unit, high-voltage system and signal probe, it realized adjustable of interrupter internal pressure and voltage load, and it is capable to simulate vacuum interrupter under various pressure condition. Finally, based on this system, the measurements within 10-3Pa ~ 1Pa were carried out with 6kV voltage load. The results show that measurement point potential has more significant change when pressure is 10-2Pa around, and it increases with the increased pressure gradually. This result share the similar laws with the simulate analyses results and has certain reference value for on-line vacuum testing of vacuum interrupter.