| Vacuum circuit breaker has a large capacity for open circuit,good arc extinguishing performance,friendly to the environment and other characteristics,so it is widely used in electric power system.Vacuum circuit breaker operated reliable in 10 kV and below for switch reactive power compensation equipment.In recent years,the vacuum circuit breaker is more and more widely applied in 35 kV system.One of the most common purposes is for switch shunt reactor.However,in the 35 kV power system,the accident characteristics of using vacuum circuit breaker to switch-off shunt reactor has obvious difference compared with 10 kV system.And because of frequent operation(hundreds of times)in a year,in some cases,accidents still happen even if the overvoltage level meets the requirements.Therefore,the fault mechanism of 35 kV vacuum circuit breaker switch-off dry type reactor is synthetically analyzed from these two aspects of overvoltage generating mechanism and the failure mechanism of turn-to-turn insulation materials(polyester film).In order to obtain the characteristics of the overvoltage,the paper set up 35 kV vacuum circuit breaker open circuit simulation model of three-phase reactor uses the ATP-EMTP electromagnetic transient simulation software.The model is set up according to the parameters,related equipment connection mode of a 220 kV substation in Yunnan,and the recorded voltage and current waveform when fault occurs.The simulation research successfully obtained the transient waveform when switch-off the reactor,and compared with the field test results.At the same time,in view of the reactor failure often shown as inter-turn breakdown,the distribution of magnetic field and electric field distribution was calculated and analyzed when turn-to-turn insulation breakdown based on finite element simulation software COMSOL Multiphysics ?.Finally,in view of the insulation fault happened when overvoltage amplitude is not high,consider the possibility of thermal aging of insulation when reactor turn-to-turn insulation materials(polyester film)long-term running at high temperatures(up to 130 °C),The influence of different aging degree and aging temperature on the insulating material(polyester film)and its performance is studied.Based on these two aspects of this research,the main research work of this paper is as follows:(1)A simulation model of vacuum circuit breaker switch-off reactor is set up based on ATP-EMTP software,considering the variety of coupling and stray capacitance.The circuit breaker switch model mainly considered the closure value when open circuit,recovery ability of dielectric insulation strength,ability of high frequency arc.These three factors are set up based on related voltage and current waveform recorded by record apparatus when open circuit reactor.Based on the simulation model,overvoltage amplitude and frequency are compared in the absence of with no protection and several kinds of overvoltage protection measures when the vacuum circuit breaker switch-off the reactor.What's more,the transient process and operation results are analyzed,the mechanism of severe overvoltage is given and several overvoltage suppression measures are put forward.(2)To analyze the distortion of electric field intensity when nanoscale gap exists at the double-layer dielectric interface,quasi static electric field calculation model is set up based on finite element analysis software COMSOL Multiphysics ?.At the same time,according to the manufacturer for the reactor design parameters,a finite element simulation model for the dry type tubular reactor has set up to analyze the electromagnetic field distribution,current change in the coil in steady state and when inter-turn breakdown occurs.In addition,the electric field distribution characteristics under power frequency and high frequency are studied.(3)Surface microstructure,dielectric constant and dielectric loss,space charge evolution characteristics,charge trap energy level,density and the electric field distortion caused by the charge of turn-to-turn insulation materials(double polyester film)are analyzed based on scanning electron microscopy(SEM),broadband dielectric spectrometer(PEA),as well as the space charge measurement platform for different aging temperature(80 °C and 130 °C)and aging degree(0 h,336 h,720 h,1000 h).the effect of thermal aging on the insulation performance is analyzed,the insulation performance degradation phenomenon during the long run time under high temperature is explained.Comprehensive above study: high frequency intercepting and more pictures combustion phenomenon are very likely to occur if installed the inappropriate overvoltage protection device when vacuum circuit breaker switch-off the reactor,formed high amplitude and frequency transient overvoltage in system and,this is the most possible reasons for the accident.But this phenomenon can be eliminated by installing RC resistance capacity absorber at parallel reactor side,which makes the amplitude and frequency of the overvoltage meet the requirements.At the same time,the simulation results based on the ATP-EMTP software is consistent with the test results;the finite element analysis software COMSOL Multiphysics ? simulation results show that when nanoscale gap exists at the double-layer dielectric interface,the electric field intensity will cause serious distortion.In case of inter-turn breakdown,magnetic field intensity in the coil is several times of under the normal operation.At the same time,the current in the coil will increase sharply.In addition to the breakdown in the coil,the magnetic flux density and magnetic flux density in other parts is consistent with the normal operation.The turn-to-turn voltage ratio at the middle of the coil and the end coil approximately the same under 10 kHz and 50 Hz;the research of the effect of thermal aging on the polyester film insulating performance shows that the surface of the material microstructure,the relative dielectric constant and dielectric loss,charge trap energy level and density,electric field distortion degree will be affected by the thermal ageing.This paper carried on the comprehensive research mainly from overvoltage and insulation these two aspects,it has important guiding significance for the 35 kV substation reactor measures to suppress the overvoltage and the selection of insulation material. |
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