Research On The New Principle And Adaptive Auto-reclosing Technique Of UHV Transmission Lines

With the UHV AC transmission model project being approved, UHV transmission project has been carried out in China. The safe and stable operation of UHV transmission system is important to the state grid because of its long power transmission distance and large power transmission capacity. Therefore the research on new principle of protection and adaptive auto-reclosing technique for UHV transmission line is of great practical significance. The main contents of this thesis are:(1) The new phase segregated current differential protection based on distributed parameter is proposed. The new protection can calculate the current at the fault point in real time, so its performance is hardly affected by distributed capacitance of transmission line. The simplified algorithm is also given to reduce computational time. The protection can also be applied to shunt compensated UHV transmission line if the current of shunt reactor is compensated.(2) The performance of transient current protection, which is based on the energy ratio of a high frequency band to a low one, is studied when it's applied to EHV or UHV transmission line. For EHV transmission line, if a higher frequency band is selected to be the low one, the protection can be more adaptive to different fault earth resistances and fault inception angles. The stray capacitance of UHV busbar is generally smaller than that of EHV busbar and high frequency current attenuates more seriously along UHV transmission line than along EHV transmission line, so the performace of such protection deteriorates when applied to long UHV transmission line.(3) To increase the operational speed of protection, the improved algorithm of energy directional protection for UHV transmission line is proposed. The protection can judge fault direction correctly after fault inception if the improved algorithm is employed. The improved algorithm is simple and can also be applied to shunt compensated UHV transmission line.(4) Two criteria for distinguishing between temporary and permanent single-phase faults on UHV transmission line without shunt reactor are proposed. The integrated criterion is based on the amplitude relationship and the phase angle relationship between the voltage at the end of the opened phase conductor and the sum voltage of two healthy phases. The criterion based on the improved correlation coefficient is proposed to distinguish between temporary and permanent faults by calculating the similarity of the voltage along the opened phase conductor and the sum voltage of two healthy phases. The integrated criterion can be applied to short UHV transmission line and the criterion based on improved correlation coefficient can also be applied to long UHV transmission line.(5) Two criteria for shunt compensated UHV transmission line are proposed to determine single-phase fault's nature. The basic principle of the two criteria is detecting the resonant component by eliminating the power frequency component in voltage or current of the opened phase conductor. For one criterion, the amplitude of resonant component is calculated from the difference of two voltages or currents of a power frequency period between which the time lag is n power frequency periods. For the other criterion, the orthogonality of sine fuctions is employed to eliminate the power frequency component in order to detect the resonant component.