Study Of Fault Location Method For Double-circuit HVDC Transmission Lines On The Same Tower

Double-circuit transmission lines on the same tower has many merits,such as narrow outlet corridor,less occupation of land resources,fast construction,alleviating the contradiction that increasingly tense land resource increases the cost of the transmission network construction,and it not only has been widely used in AC system,but also has found application in DC system in recent years,namely the double-circuit HVDC transmission lines.Long-distance HVDC transmission lines are subject to faults,hence it is important to locate fault position to accelerate the restoration from serious blackout,reduce the outage time,and improve the AC-DC interconnected power system reliability.However,comparing with the traditional bipolar HVDC transmission line,double-circuit HVDC transmission lines on the same tower have complex phase-phase coupling and line-line coupling.Moreover,double-circuit HVDC transmission lines cannot be seen as the balance parameters,because of the asymmetric transposition,thus the electric quantities cannot realize the fully decoupling by utilizing the simple phase mode transformation.These factors make it more complicate on fault location than single-circuit transmission line.Thus,as more and more application of the double-circuit HVDC transmission lines on the same tower,the study of fault location with DC double transmission lines on the same tower has important theory significance and application value.Therefore,the phase-mode transformation method and the fault location method are studied.The main work is summarized as following:(1)The electromagnetic coupling characteristics of single /double-circuit HVDC transmission line are analyzed.The phase-mode transform method suitable for double-circuit HVDC transmission line is explored.The numerical decoupling with double-circuit HVDC transmission line and the distribution characteristic of the model traveling-wave with different fault polar are analyzed,laying the foundation of putting forward the fault location methods for double-circuit HVDC transmission lines.(2)Considering the control and protection of each circuit are still based on the single-circuit electrical quantities in practical project,the characteristic of each modulus when fault occurs on different polar lines is studied based on the single-circuit electrical quantities.Then the calibration of travelling wave and selection of wave velocity are investigated.Based on this,a traveling-wave fault location method for double-circuit HVDC transmission lines on the same tower based on single-circuit electrical quantities is proposed.The PSCAD/EMTDC simulation model of Xiluodu-Guangdong ±500kV double-circuit HVDC transmission lines on the same tower is constructed and extensive simulation is taken to verify the method.(3)In order to further improve the completeness of the fault location algorithm,the time-domain fault location method for double-circuit HVDC transmission line based on single-circuit quantities is proposed in this paper.Aiming at the problem that the differential-mode component and the comment-mode component both concludes earth-mode by utilizing the single-circuit transformation matrix,the new differential-mode component,which eliminates the influence of the earth-mode,is constructed.The characteristics and parameter selection of the new differential-mode component are also given.Considering the characteristic that the voltage distributions of non-fault point calculated by the voltage and current measured in both terminals have largest difference at fault time,the maximum voltage difference zone of the non-fault point is defined.Extensive simulation results have shown that the proposed method is not only with high accuracy but also meets the requirement of actual project.