Research On Line Protection Of Distribution Network Based On 5G Communication Technology

The traditional distribution network mostly adopts single point to multi-point radial one-way energy transfer structure.The protection method is mainly stage current protection,and the selectivity of action is guaranteed by time limit,which has the problem of long action delay.With the access of Distributed Generation,the distribution network has developed from passive to multiple sources,and from a single grid to multiple grids.These changes make the traditional protection method based on single terminal appear some problems,such as slow operation speed,misoperation,refusing to operate and so on.Obviously,the protection method based on single terminal can not adapt to the network of multi terminal power supply.Differential protection is widely used in transmission lines as the representative of double terminal electrical quantity protection,and has become the first choice in many occasions.Due to the high synchronization requirements of differential protection for bilateral data,optical fiber has been used as transmission channel in transmission lines,which can meet the requirements of differential protection for transmission delay.However,considering the high infrastructure cost of optical fiber communication,it is very difficult to set up optical fiber in distribution network,so differential protection has not been widely used in distribution network.The arrival of 5G provides a transmission channel that can replace optical fiber for differential protection based on double ended electrical quantity.Its performance can meet the requirements of protection in theory,and it is fast to deploy,low-cost and easy to upgrade.Therefore,this paper combines 5G technology with distribution network protection,and studies many problems of 5G technology in distribution network,aiming to provide a new idea for distribution network protection.Firstly,the protection methods commonly used in distribution networks are introduced,and the impact of Distributed Generation access on traditional distribution network protection is analyzed.The comparison results reveal that differential protection,which is based on two-ended electrical quantities,is more adaptable to electric distribution networks with Distributed Generation access.Secondly,based on the protection of two-ended electrical quantity,the core problem is data synchronization.This thesis compares the advantages and disadvantages between the interpolation synchronization method based on device timing and the synchronization method based on fault time alignment,and selects a synchronization method based on fault time alignment which does not need to add a timing device and is not affected by the channel.The accuracy of this method depends on accurate fault time detection.Therefore,this thesis proposes a fault time detection method based on Hankel matrix singular value decomposition,which completes data synchronization by aligning the fault time detected on both sides.Simulation results show that the fault time detection error of the proposed method is extremely small.Thirdly,from the perspective of protection principle,this thesis studies the protection method of electric distribution network,and proposes a differential protection method based on DTW(Dynamic Time Warping)algorithm.Compared with the traditional current differential protection,this method moves quickly and requires less transmission channel,which is very suitable for wireless media with delay jitter such as 5G transmission.Besides,in order to make up for the deficiency that differential protection cannot reflect small current grounding fault,this thesis supplements the above protection methods from the perspective of transient energy,thus forming a complete set of distribution network protection scheme.Finally,the reliability of the proposed synchronization method and protection method is verified by the test in real 5G environment simulated and built through PSCAD/MATLAB.