| The main obstruction, which prevents vacuum circuit breakers' transmissions to high-voltage levels, is that the characteristic of the dielectric strength of an electrode arrangement in vacuum increases only degressively as the gap length increases above 10-15mm. That indicates a direction to keep the advantages of short-gap vacuum interrupters by means of using vacuum circuit breakers (VCBs) with double or multiple breaks. The idea of a double and multi-break VCB is to use the high electric strength of vacuum in small flashover distances. We want to reach a higher breakdown voltage with the series connection of two or more breaks in comparison to single break with the same clearance.A novel VCB with multiple breaks based on fiber-controlled vacuum interrupter modules (FCVIMs) is presented in this paper. The FCVIM is mainly composed of outer insulation, vacuum interrupter, permanent magnetic actuator (PMA), independent operating power supply and fiber-controlled system. A retrofit VCB with multiple breaks can be realized by placing some FCVIMs in series just like the building blocks. Its number in series can be designed for demands in actual high-voltage class. In the meantime, the breakdown statistical property, the static dielectric property and electric distribution in VCB with multiple breaks are researched herein.Firsty, the technical development of VCB with single or multiple breaks and essential dielectric property in vacuum are described.Secondly, based on the dynamic dielectric recovery process on the vacuum gaps in series, investigations are made on post-arc insulation state on multiple breaks operation in high voltage power system. From the research on the breakdown weak points in high voltage vacuum gaps, their turn out and distribution, some theoretic work are made to set up the models for describing the breakdown statistical property of VCB with multiple breaks, which can be used for explaining the mechanism on the improvement of the breaking capacity for multi-break units compared with single-break ones which have the same equivalent gap length.Thirdly, a novel VCB with multiple breaks based on FCVIMs is presented herein. The FCVIM is mainly composed of outer insulation, vacuum interrupter, permanent magnetic actuator (PMA), independent operating power supply and fiber-controlled system. The components are narrated in details. The designs of electromagnetic compatibility and reliability are proposed.Fourthly, a new VCB with multiple breaks can be realized by placing the FCVIMs in series just like the building blocks. The needed numbers can be designed for demands in actual high-voltage grade. Compared with conventional VCBs with multiple breaks, it has a significant reduction in size, weight and cost as well as simpler control and better operating synchronization among its breaks. For the continuous electric field optimization, the model of a 12kV vacuum interrupter in the FCVIM is set up for 3D electric field computing using the ANSYS finite element program. By means of calculations of different collocations of VCB with double or triple breaks based on FCVIMs, the optimized electric field design is proposed for applications. The capacitance equivalent circuit is put forward for simulating the voltage distribution of the breaks.Lastly, by means of a mass of experiments on the vacuum interrupter arrangements with single break or triple breaks in series, the breakdown voltage improvement factor, breakdown statistical property and electric distribution in breaks are researched. It shows that the capacitance equivalent circuit is suitable for simulating the voltage distribution of the breaks. Proper compensating capacitance can optimize the electric field distribution in VCB with multiple breaks. The experimental results show that the operation time of a sample FCVIM decreases with the increment of the charged voltage in storage capacitor. The deviation on the operation time of a sample 40.5kV FCVIM is less than 1ms.
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