Study On Measures For Voltage-sharing During Interrupting Process Of Vacuum Circuit Breaker With Multiple Breaks In Series

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 lebgth increases. That indicates a direction to keep the advantages of short-gap vacuum interrupters by means of using vacuum circuit breakers(VCB) with multiple breaks. In order to improve simultaneity of closing or opening and insulation performance of VCB with multiple breaks, Dalian university of technology presented a novel VCB with multiple breaks based on fiber-controlled vacuum interrupter modules(FCVIMs).This thesis mainly research simulation model of dielectric recovery and reignition and measures of voltage-sharing during interrupting process of 126kV FCVIM with triple breaks. The main subject investigated is dielectric recovery characteristic and EMTP model building of VCB with multi-breaks. The influence of power system on dynamic dielectric recovery of VCB, the voltage-sharing behavior and reignition behavior of FCVIMs and the optimization configuration of equalizing resistance and capacitance are researched through analyzing, EMTP simulating and testing.Firstly, the technical development of VCB with multiple breaks is retrospected. The dielectric recovery and reignition characteristic during interrupting process of VCB in series are described. The earlier research findings are exploded. The research purposes are generalized. The dielectric recovery microscopic process of vacuum gap, including of arc extinguishing process, electron current attenuation process and post-arc dielectric recovery process, are analysed. The reignition modes, including of field-breakdown, thermal breakdown and Paschen limit breakdown, are analysed.The EMTP model of simulating dielectric recovery process of vacuum gap is mainly developed. In order to overcome the shortage of original EMTP model, the models of frequency, neutral copper vapor density, ion density, ion velocity, initial post-arc current and action of contact are introduced to connect initial ion density, initial ion velocity and initial current of post-arc process with arc current and action character of contact. The unified modeling of VCB and power system is truly realized. The accuracy of EMTP model of simulating dielectric recovery process of vacuum gap is verified by comparing simulation results with test data obtained by Edward Huber. The accuracy of EMTP model of simulating action character of contact is verified by comparing simulation results with test data obtained by Yuan Shun and Wang Jimei of Xi’an Jiaotong University.The influences of fault type and shunt capacitance and resistance on VCB are researched to provide influence index of fault parameters on dielectric recovery characteristic of VCB in series for latter research. The research results, those the dielectric recovery characteristic of VCB is most serious when breaking two phase short circuit current, shunt capacitance should not be too large, shunt resistance can improve he dielectric recovery performance of VCB, are obtained.The other research imphasis is to put forward rational measures of voltage-sharing for VCB with multi-breaks in series.Reasons producing non-conforming of voltage assignment are researched. The theory and the action of shunt capacitance and resistance in voltage-sharing are vertified by EMTP simulation. The effect of prebreakdown on voltage-sharing is researched by theoretical derivation and test analysis. The reignition characteristic of VCB with multi-breaks in series and the overvoltage produced by reigntion are researched by theoretical derivation and EMTP emulation. Based on the effect of shunt capacitance and resistance on dielectric recovery of VCB with multi-breaks in series, the optimal allocation of shunt capacitance and resistance is obtained to improved the voltage-sharing of VCB with multi-breaks.Finally, the voltage-sharing way of 126kV FCVIMs with 1500pF grading capacitance, or with 500pF grading capacitance and 500Ωgrading resistance are obtained to service practical application. The better result with 1500pF grading capacitance is verified by EMTP emulation.