Dynamic Insulation and E-Stress Sharing in Transmission-level Vacuum Circuit Breakers

A transmission-level vacuum circuit breaker (TVCB) is a high-tech power device that major companies have been competing to develop in recent years. The technical bottleneck for the development comes mainly from the more severe electric field stress (E-stress) in the working scene and the dynamic insulation deterioration. The saturation effect of the breakdown voltage on the vacuum gap separation forces the electrode structure design to be magnified geometrically, causing new technical problems in the multi-physical field. In terms of enhancing the dynamic insulation level of TVCB, it is necessary to focus on the weak-point of breakdown (WP) to form a mechanism for strengthening the dielectric recovery. Combined measures to restrain WPs includes: re-examining the selection of contact materials and the structural design of the interrupter for intercepting WP, defining WP states parameters, forming a closed-loop control of deep conditioning, and finally, expanding dynamicconditioning procedures and in-service maintenance requirements.The tolerance of E-stress is the underlying logic from the perspective of the field source. Along the path of E-stress sharing, the traditional TVCB electrode system can be converted to a back-to-back series structure of a vacuum interrupter pair (VIP), with each separation of the pair set in the linear growth region of the breakdown/separation curve. So the axial E-stress sharing of the main gap can be completed under the unchanged spatial scale. Several floating potential shields are set up, together with the main shield, formed an auxiliary gap channel parallel to the main gap. It can further share the E-stress radically. In addition, the finely designed floating shields can also balance the distribution of TRV inside the VIP.Taking the VIP electric field design of 252kV-TVCB as an empirical research case, the modeling and simulation of the VIP equivalent electrical network were completed. By the analysis of the VIP dual-ended drive and the discussion of the multi-break synchronization control, the module framework design and VIP prototype for 252kV-TVCB have been completed. The high-voltage test device for the factory inspection of the vacuum interrupter is used to test the voltage parameters of the VIP prototype.The empirical research results show that, the E-stress sharing is a practical strategy to increase the working voltage of TVCB. The comprehensive management of WP can make up for the technical shortcoming of TVCB relative to SF6 in dynamic insulation. The vacuum interrupter pair form can increase the working voltage and dynamic insulation level. Unlike the conventional double-break VCB, the pair structure shares a break-node, which reduces the influence of the distribution parameters, so as to obtain higher series efficiency. Furthermore, the discrete welding of VIP can also significantly reduce the manufacturing difficulty and production cost of TVCB.