| UHV project has the advantages of long distance,large capacity,low loss,and it has become an inevitable choice to solve the contradiction between energy and development in China.With the expansion of the transmission power and the increase of the transmission voltage,the reactive power fluctuation of the system will be more frequent,and the traditional simple power compensation method has not been able to meet the requirements of UHV Engineering.In order to meet the requirements of UHV reactive power compensation and limit the overvoltage of the system,a series of hybrid reactive power compensation methods can be adopted.Circuit breaker will have high recovery voltage when interrupt out of step fault and all kinds of short-circuit current,may cause damage to the insulation.In view of the transient characteristics of UHV transmission line after fault,this paper will make a deep and detailed study on the breaking characteristics of the circuit breaker from the aspects of the transient recovery voltage and the arc extinction characteristics of the potential power supply.The main work is based on several aspects:On basis of the introduction of key components and the structure of hybrid reactive compensation,simulation analysis was carried out on the characteristics of circuit breaker when out-of-phase fault occurs in the UHV transmission line with hybrid reactive compensation,the variation rules of the out-of-phase fault current and transient recovery voltage of circuit breakers were obtained.Using equivalent lumped parameter circuit,the computational formula of the fault current and transient recovery voltage rising rate are deduced and computed.In the light of the most common single-phase earth fault and the most serious three-phase short circuit fault in UHV transmission line,by using the numerical analysis and simulation,the variation of the transient recovery voltage rise rate and the transient recovery voltage with the compensation of the hybrid reactive power compensation is obtained,and detailed theoretical derivation.For different faults,the transient recovery voltage oscillation frequency is analyzed and compared from the time and frequency domainIn order to study the secondary arc characteristics of single-phase transient fault in UHV transmission lines with hybrid reactive compensation device,this paper established a perfect transmission line electromagnetic coupling model.Dynamic model of secondary arc was established on the basis of improved Mayer equation,based on the transient simulation and the method of Laplace,the influence law of secondary arc characteristics in UHV transmission lines with hybrid reactive compensation was obtained.By changing different compensation degrees of series compensation and controlled shunt reactor?neutral reactor?secondary arc resistance,each frequency component of the secondary arc and the changing rule of secondary arc burning time were obtained by the simulation analysis,and theoretically expounds the mechanism of oscillation.Based on the specific compensation device configuration scheme,a time sequential control strategy between the bypass switch and single-phase autoreclosure were put forward,which provides a theoretical guidance for practical application.In order to obtain the evaluation criteria for measuring the difficulty of breaking the circuit breaker,the numerical simulation and simulation analysis of the relevant parameters of the circuit breaker interrupting performance(breaking severity scale)are carried out,this paper puts forward the evaluation system of the arc extinguishing mode and the breaker breaking difficulty.In Southeastern-Nanyang-Jingmen UHV AC demonstration project as the research background,discuss the system out of step fault,the midpoint of the single-phase short-circuit breaker grounding fault and three-phase grounding fault when breaking transient characteristics,and then use the formula to obtain the fault severity evaluation of the most serious impact on the demonstration project,which has instructive effect on the structure of the circuit breaker design. |
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