| Multi-break vacuum circuit breaker composed of multiple single-break vacuum circuit breakers connected in series overcomes the saturation effect under long vacuum gap and retains the excellent insulation capability under short vacuum gap.It is considered as a possibility to replace SF6 circuit breaker in the field of high voltage and ultra-high voltage.In recent years,it has become a research hotspot in the field of high voltage electrical apparatus.In practice,it has been found that during the breaking process of multi-break vacuum circuit breakers,the uneven voltage distribution of each break will lead to unsuccessful breaking,which limits the development of vacuum circuit breakers to the field of high voltage.In order to solve this problem,this paper proposes to add the external magnetic field on the basis of the existing structure.It can control the arc in the arcing stage and achieve the purpose of equalizing the voltage of each break.The combination of theoretical analysis,simulation and experiment was adopted.Magnetic field control mechanism and measures for dynamic voltage distribution of multi-break vacuum circuit breaker were studied.This paper firstly introduces the current status of multi-break voltage equalization research and multi-break magnetic field control research.It has been found that most of the previous studies using synchronous magnetic field regulation for voltage equalization.And non-simultaneous control methods were rarely reported.Therefore,a non-simultaneous external magnetic field control scheme was proposed.Then,the effects of the magnetic fields generated by various types of contacts and the external magnetic fields on the vacuum arc were theoretically analyzed respectively.The results of the effects of various types of magnetic fields on the vacuum arc were obtained.It provides theoretical support for external magnetic field control measures.Using simulation software such as Maxwell and Simulink,the magnetic fields generated by various contacts and Helmholtz coils were simulated to verify the correctness of the theoretical analysis.At the same time,the results of different combinations of contact and external magnetic field were analyzed.it was concluded that the combination of axial magnetic contact and external axial magnetic field was more effective for magnetic field control experiment.Based on the calculation and simulation results,an external magnetic field control system for double-break vacuum circuit breaker was designed.It includes three parts: power supply,control unit and magnetic field coil.The system can precisely control the external magnetic field with a strength of 0-120 mT and an adjustable pulse width of 2-10 ms.And it can After calibration,its performance meets the experimental requirements and can be used to generate a precise and controllable external magnetic field.Finally,external magnetic field control experiments were done on the magnetic field control experimental platform for double break Vacuum circuit breaker.In the experiments,the integrated double-break vacuum chamber was used as the test switch,and the self-designed magnetic field control system was used to adjust the dynamic voltage distribution of the double-break vacuum circuit breaker during the breaking process.The influence law of the magnetic strength of the external magnetic field and the applied time of the external magnetic field on the dynamic voltage distribution were obtained.And the best magnetic field control method under this test condition was proposed.When magnetic field strengths of two breaks are both 60 mT.The applied time of high-voltage side break is 4ms after the current is generated,and the low-voltage side break is 7ms after the current is generated.At this time,the minimum unevenness coefficient is 14.4%.The results provide references for the future research and design of multi-break vacuum circuit breakers. |
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