Electromagnetic Field Analysis On Medium Voltage Direct Current Vacuum Circuit Breaker

Vacuum circuit breakers(VCBs),using the vacuum as the insulation and arc extinguishing medium,have been widely used in medium voltage power systems.With the development and application of new energy technologies,the development and needs of power distribution systems,direct current(DC)medium voltage VCBs which combined commutation technology and mechanical have become the focus of the researchers.Vacuum interrupter(VI)is the core component of the VCBs,and the dynamic and static insulation characteristics of the VI will directly affect the operating property of the VCB,and the safety,reliability and stability of the power system.The active DC VCB is taken as the research object.Based on the analysis of the commutation circuit and the VI of the DC VCB,the effects of the commutation parameters,such as the inductance and capacitor are taken into consideration,and the insulation properties of the VI and magnetic characteristics variation are studied.Based on Kirchhoff’s law,the differential description of the DC VCB during the interrupting process is presented.And the insulation influence factors for the uniformity of the electric field distribution in the VI have been studied.Moreover,the electric field computation model of the axisymmetric VI was established.Using the finite element method(FEM),the electric field distribution of the VI and the distribution of the electric field strength along the major components of the DC VCB were obtained under different commutation frequency and boundary conditions.Through the numerical simulation and analyses of the electric field distribution of DC VI in 15 kV and 24 kV single-break DC VCB under different commutation frequency and no-load breaking process,the electric field variation has been quantitatively analyzed,and the distribution of electric field strength along the contour of the shielding cover were studied.Based on the FEM numerical analysis platform,a three-dimensional magnetic field model of the VI with cup-shaped longitudinal magnetic contact was established.And the transient magnetic field of the four-slot and six-slot structure on the contact cup wall was numerically simulated and analyzed under different commutation frequencies.The influence factors of magnetic blowing ability in the magneto-thermal process were obtained,and the three-dimensional distribution of the vertical magnetic field and the comparison of the arc center plane under typical commutation frequencies,the current peak moment and the current zero are obtained.