The Improving Effect of Parallel Capacitors on the Internal Potential Distribution of Vacuum Interrupters
Insulation is a crucial factor in the performance and reliability of vacuum interrupters.Previous research has found that placing vacuum interrupters in grounded metal enclosures can cause potential offsets in shields and reduce the insulation performance of vacuum interrupters.This study establishes an equivalent circuit model to improve internal potential distribution by adjusting shield potential with parallel capacitors.As a result,paralleling capacitors on the order of hundreds of picofarads can effectively improve the potential shift of the interrupter.In experiments,the measured main shielding potential of the vacuum interrupter is about 34%of the total voltage in its natural state.By paralleling 500 pF capacitors,the potential of the main shield can be improved to 49%.Two capacitor parallel schemes are proposed and compared with multi-stage floating shield structures.The paper investigates the influence of ground position variations on the internal potential and electric field distribution of the vacuum interrupter.The stray capacitance parameters of the vacuum interrupter are extracted,and an equivalent circuit model of the vacuum interrupter is established.Secondly,a method is proposed to adjust the potential of the shield in the vacuum interrupter using parallel capacitors.Based on the equivalent circuit model of the vacuum interrupter,the influence of parallel capacitors on the internal potential and electric field distribution of the vacuum interrupter is studied.Experiments are designed and conducted to measure the floating potential of the shield in the vacuum interrupter.The differences in the shield potential between parallel and non-parallel capacitors are compared,verifying the effectiveness of the proposed method.Finally,for high voltage level vacuum interrupters with multi-stage floating shield structures,differential effects of different parallel configurations on the internal potential distribution improvement in the vacuum interrupter are studied.The following conclusions can be drawn.(1)By paralleling capacitors in the vacuum interrupter,the potential can be adjusted,and the internal potential and electric field distribution can be improved.Generally,the stray capacitance of the vacuum interrupter is on the order of tens of picofarads.When the value of the parallel capacitors is in the hundreds of picofarads,ideal improvement can be achieved.(2)The floating potential of the shield in a 40.5 kV vacuum interrupter was experimentally measured.The experimental results show that the potential of the shield in this 40.5 kV vacuum interrupter is approximately 34%of the total voltage under the experimental conditions.By paralleling a 500 pF capacitor between the moving/static terminal of the vacuum interrupter and the shield,the potential of the shield can be adjusted to 49%of the total voltage.(3)For high voltage level vacuum interrupters with multi-stage floating shield structures,there are two strategies for parallel capacitors:adjusting the potential of only the main shield or all floating shields.Both strategies can achieve ideal results.Considering economic costs and practical application conditions,adjusting the potential of only the main shield is the preferred choice.
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