Research On The Influence Of Frequency Fluctuation On Power Line Protection

The power grid is a dynamic and complex system.When disturbed,the electrical frequency,voltage,current and other electrical quantities will fluctuate.When some operating conditions in the actual power system,such as the isolated network operation,the frequency fluctuates greatly.In addition,the grid frequency fluctuation is closely related to the capacity of the grid.In 2016,the Yunnan Power Grid and the Southern Main Network were implemented as the sending end.Asynchronous interconnection,the capacity of Yunnan power grid is about 1/7 of the capacity of the southern power grid,and it is sent by large-capacity DC.Complex faults will cause large fluctuations in frequency caused by severe shortage or excess of local active power,while power protection uses power frequency.The method of measuring,when the grid frequency deviates from the power frequency,the protection electrical measurement may have a large error,which leads to protection misoperation or refusal,which poses a serious threat to the safe and stable operation of the power grid.In view of the above practical problems,power line protection is the main research object.Through theoretical derivation,simulation analysis and other means,the influence of frequency fluctuation on Fourier algorithm is deeply studied.Based on this,the frequency fluctuation is applied to the line protection action range.The influence of sensitivity,etc.,gives the frequency fluctuation boundary and mechanism that protection does not work correctly.Finally,the corresponding solutions are proposed.The main research contents and results of the thesis are as follows:Firstly,the influence of frequency fluctuation on the Fourier algorithm under different factors is derived theoretically.The derivation shows that the voltage,current amplitude,phase angle and impedance calculated by the Fourier algorithm have errors,the magnitude of the error and the frequency fluctuation.The magnitude has a direct relationship.Secondly,the corresponding protection simulation model is constructed based on the principle of different protection.The influence of frequency fluctuation on different protection is analyzed by simulation.The simulation results show that it is consistent with the theoretical derivation.That is,the frequency fluctuation has no effect on the power line current protection and differential protection,and the frequency fluctuation has a certain influence on the action behavior of the distance protection,resulting in the phenomenon that the protection appears to be rejected.Finally,based on the existing literature to propose a modified Four's algorithm,the applicability of the modified algorithm in the specific line protection is analyzed to reduce the impact of frequency fluctuation on the line protection,and the adaptation is explored.The power grid protection method under dynamic frequency changes has important academic and scientific research value,which can ensure the reliable and correct operation of line microcomputer protection under frequency fluctuations,and has important practical value for ensuring safe and stable operation of power grid.