Fault Location And Protection Methods Based On Natural Frequency Prediction-correction For VDC Transmission Lines

With the continuous construction of smart grid,HVDC of high voltage and large capacity plays a very important role in the safe and stable operation of power grids.But the DC line is generally long,and it always goes through complex terrain or harsh environment,as a result,the risk of faults is great and it's difficult for fault location.So study of fast and accurate for DC line fault location and protection method and device has been a hot research in electric power engineering.At present,the mainly fault location method of HVDC transmission lines is traveling wave method in time domain.At the same time,fault location method in frequency domain is studied.But all the methods have their own advantages and disadvantages.For example,time domain method is limited to the recognition of wave head and frequency domain method is limited to aliasing of frequency.Therefore,a new fault location and protection method and its algorithm are put forward by fusion of the characteristics in time domain.Firstly,the fault characteristics of HVDC system is analyzed and on the basis the general ideology of fault location and protection based on natural frequency is proposed by using the relationship between the transient component of fault current and fault distance.Secondly,in order to decrease the influence of the aliasing of natural frequency,this paper makes full use of the rough fault location result by using two-terminal traveling wave fault location method.Through the method to define the real range of natural frequency,that is the natural frequency prediction.Then wave analysis and MUSIC algorithm are used to determine the natural frequency,that the correction of natural frequency.Use this natural frequency to calculate the fault distance,and that is the practical fault algorithm of location based on the natural frequency prediction correction of fault current transient component.Thirdly,natural frequency difference of faults of AC side and Converter Station and District external fault are analyzed,and based on the different characteristics of the natural frequency,the protection criterion is put forward in order to realize the judgment of the DC system area within the region or outside fault,that the frequency difference protection.At last,a HVDC system is established in electromagnetic transient simulation software PSCAD/EMTDC,and conditions of different fault distance,different transition resistance are simulated,then fault algorithm of location practical based on the natural frequency prediction correction of fault current transient component and its Matlab algorithm program are tested.Test results show that the fault location method has high accuracy and the proposed line protection is feasible.