Study On Simulation Comparison And Protection Optimization Of Niucong HVDC Typical Faults

The Niuzhai-Conghua Extra-high Voltage System(Niucong EHV)is the world's first ±500kV EHV DC transmission project with common-tower double-transmission lines.It spans a total of 1251 kms from Niuzhai,Yunnan province to Conghua,Guangdong.Niucong EHV DC transmission system was completely put into operation on June 2014,and more than half of the average power supply load of Guangzhou can be covered by Congxi Converter Station.This paper introduces the composition and function of the Niuzhai-Conghua Extra-high Voltage System protection.The results of fault and protection action are analyzed since Niucong HVDC putting into operation.The Niucong HVDC control protection system reliability is analysised,which can improve the optimization of itThe two typical failures in HVDC system are simulated,including commutation failure and DC line failure,and study their control and protection strategies.For commutation failure,analyzing its failure mechanism,the failure causes is summarized,some factors on the occurrence of commutation failure are calculated and analyzed.The additional control and protection function modules of commutation failure is proposed based on its basic protection strategy,respectively,from the AC-DC current differential,AC system symmetric fault,AC system asymmetric fault to the corresponding increase in turn-off angle value.The theoretical analysis and simulation results found that the module commutation failure recovery process is more quickly and effectively.For the DC line fault,analyze the fault mechanism and study the different types of characteristics of DC line faults,on the base of these research puts forward the DC line fault control and protection strategy.Two typical traveling wave protection principle,the affected factors and the operating characteristics are simulated and analyzed,also making some improvement of traveling wave protection and the simulation results show that it can be more accurate to detect high impedance ground fault and improve action performance.Finally,based on the project research needs,and combined with the typical failure of control and protection strategies,the HVDC control and protection system for building the framework for the relevant theoretical content is studied in three aspects: the functional requirements of the system,the basic principles for the configuration and design of the system and all levels functions and range of control.