| The Ultra High Voltage(UHV)project with long transmission distance,large transmission capacity,and low energy loss has become an inevitable choice to solve the contradiction between energy and development.With the expansion of transmission power scale and increase of transmission voltage,the reactive power fluctuations of the system will become more frequent,and the traditional simple power compensation method can no longer meet the requirements of UHV projects.In order to meet the requirements of UHV reactive power compensation while limiting the system's over-voltage,hybrid reactive power compensation(HRPC)methods with series compensation and stepped controlled shunt reactor can be used.When the UHV system breaks down,there will be a higher transient recovery voltage generated in the circuit breaker,which affects the opening of the circuit breaker and may cause damage to the insulation.Aiming at the transient characteristics of UHV transmission lines after installation of HRPC equipment,we will study the interrupting characteristics of circuit breakers from the aspects of transient recovery voltage and interrupting current.The main work focuses on several aspects:According to the actual structure of the UHV demonstration project line,the characteristics of the UHV transmission system installed with HRPC after single-phase ground fault occurs are simulated and analyzed to obtain the interrupting current and the change law of transient recovery voltage.Based on the equivalent-valued parameter circuit,the calculation formulas affecting the interrupting characteristic of circuit breakers are deduced,and the influence of factors such as the fault location and the HRPC compensate degree on the interrupting characteristics of the single-phase ground fault circuit breaker is analyzed.Based on the equivalent impedance network and Laplace transform equation,the oscillation frequency and attenuation coefficient of the free component of the secondary arc current are deduced,and the formation mechanism of the free component of the secondary arc current is quantitatively explained.The effects of small neutral reactance and HRPC compensation on the low-frequency component frequency and attenuation speed of the free component of the secondary arc current are analyzed.Finally,a set of auto-reclosing control method that help the secondary arc to be extinguished faster is proposed.The numerical calculation and simulation methods are used to study the relevant indicators of the interrupting characteristics of the circuit breaker under different faults.In order to obtain the evaluation standard of the interrupting difficulty of the circuit breaker,the relevant indicators of the interrupting performance(interrupting severity scale)of the circuit breaker in various faults is obtained through the numerical calculation and simulation analysis.Based on the arc extinguishing method of the circuit breaker and the arc extinguishing medium,an evaluation index for the severity of the circuit breaker is proposed.With reference to the relevant parameters of the UHV AC test demonstration project of Jindongnan-Nanyang-Jingmen,the transient characteristics of the circuit breaker for single-phase ground fault,phase-to-phase fault,two-phase ground fault,and three-phase ground are discussed.Then compare the interrupting current,transient recovery voltage and severity scale of the circuit breaker under different faults.With the reference to the arc-extinguishing principle of the UHV SF6 circuit breaker,a geometric model of the 1100kV UHV SF6 circuit-breaker is established.Based on multiphysics software,the electric field parameters of the arc extinguishing chamber before and after the installation of HRPC are numerically simulated,and the effect of HRPC on the dielectric recovery characteristics of the circuit breaker is analyzed.The influence of HRPC on the circuit breaker opening characteristics is studied from the field perspective. |
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