Design And Optimization Of Integrated Voltage Self-sharing Vacuum Interrupter For Series Connection

Vacuum circuit breaker is an environmentally friendly switchgear that is widely used in the field of medium voltage distribution.Due to the saturation effect between the vacuum gap breakdown voltage and the gap length,the development of singlebreak vacuum circuit breaker to a higher voltage level is restricted,and multi-break series technology is one of the technical routes to achieve ultra-high voltage vacuum circuit breakers.The difference in the stray capacitance parameters of each break of the multi-break vacuum circuit breaker to the ground leads to uneven distribution of the voltage of each break,and the conventional voltage sharing configuration adopts the parallel voltage equalization capacitance or capacitance element at both ends of the vacuum interrupter.Due to the tank grounding and compact design,each break of the tank type multi-break vacuum circuit breaker and the main shielding cover of the vacuum interrupter increase the stray capacitance to the ground,and the compact pressure sharing configuration of the tank type multi-break vacuum circuit breaker is urgent.In view of the compact pressure sharing requirements of the tank type multi-break vacuum circuit breaker,this paper proposes a new structure of a 40.5 kV series dedicated voltage self-sharing vacuum interrupter based on the integration of ring ceramic capacitor and external pressure equalizing shielding cover,and theoretically analyzes its structural composition and working principle.A 3D model of a 40.5 kV voltage self-sharing vacuum interrupter was built using three-dimensional modeling software,and the configuration scheme of the voltage self-sharing vacuum interrupter was determined through COMSOL electric and thermal field simulation calculation:the thickness of the inner and outer epoxy resin is 5 mm,The external voltage equalizing shield is an aluminum bowl-shaped structure with a height of 59 mm and an edge chamfering radius of 30 mm.The connection method between the external pressure equalizing shield and the ring ceramic capacitor is that the end of the outer pressure equalizing shielding cover is tangent to the outer epoxy along the surface,and the corner radius at the connection is 10 mm.At the same time,based on the designed 40.5 kV voltage self-sharing vacuum interrupters connected in series to form a multibreak vacuum circuit breaker for electrostatic field simulation,the main shield suspension potential pressure ratio,break-to-break average pressure ratio and other parameters were calculated.Referring to the simulation results,a prototype of the voltage self-sharing vacuum interrupter was developed.Built a test platform,and tested and measured the potential of the main shield of the vacuum interrupter and the voltage distribution between the breaks under the power frequency high voltage and highfrequency transient recovery voltage of the new structure voltage self-sharing vacuum interrupter.The simulation results show that compared with the commercial vacuum interrupter,the voltage self-sharing vacuum interrupter reduces the maximum external electric field strength from 0.97 kV/mm to 0.45 kV/mm,and at the same time makes the internal potential tend to be evenly distributed in the middle of the vacuum interrupter,which improves the distribution of the electric field inside and outside the vacuum interrupter,thereby improving the internal and external insulation performance.Under the same current-carrying conditions,the voltage self-sharing vacuum interrupter effectively reduces the temperature rise of the vacuum interrupter compared with the commercial vacuum interrupter.The voltage distribution ratio of each break of the multi-break vacuum circuit breaker composed of voltage self-sharing vacuum interrupter in series is 34.27%:33.14%:32.59%,and the average pressure ratio of the main shielding cover of each break after series connection is higher than 49.79%.The test results show that the double-break vacuum circuit breaker composed of the voltage self-sharing vacuum interrupter in series has a break-up voltage ratio of 52.81%:47.19%under the power frequency high voltage,and the average pressure ratio of the main shielding cover of the vacuum interrupter on the high-pressure side is 48.94%,the differential pressure ratio of the break is 53.94%:47.19%under the high-frequency transient recovery voltage,and the average pressure ratio of the main shielding cover of the high-voltage vacuum interrupter is 44.17%.Through the comparison of test data and simulation results,it is shown that the voltage self-sharing vacuum interrupter in series can realize the pressure sharing control between the main shielding cover and the series break,and its compact structure and small insulation space requirements can meet the compact pressure sharing requirements of the tank type multi-break vacuum circuit breaker,and provide technical support for further development of the tank circuit breaker of 252 kV and above voltage level.