Study On Fault Location Schemes For Power Grid Considering The Feature Of Traveling Wave Velocity

Transmission lines play an important role in the process of power transmission.Relay protection is necessary to ensure the stable operation of system.The protection can break the fault lines and locate the fault point when a fault happened,which is convenience for people to repair faults quickly.Also,it can avoid the expansion of faults and reduce the loss caused by blackouts.Fault location greatly improve the stability of power system.This paper analysis common fault types in transmission lines firstly.Considering the factors of relay protection,economics synthetically,this paper makes a deeper research about fault location in grounding faults,which is 80% of all faults.A fault location method for asymmetrical grounding faults is proposed based on the time difference of different modes(TDOM)arrived in measured points.Firstly,the energy attenuation characteristics and the frequency dependence characteristics of the traveling wave are used to analyze the nature of traveling wave speed variation.It is proved that the wave speed of line-mode can be regarded as a constant in the application,and the speed of the zero mode varies with the distance,which has an internal relationship with the fault location.Therefore,by analyzing the variation of zero mode traveling wave,the trend of zero-mode traveling wave velocity is quantified.Through the combination of simulation and actual measurements,the quadratic function of wave velocity variation is determined.The expression gives a least-squares fitting method for the variation of zero-mode traveling wave speed along the length of lines.The proposed quantification method turns unfavorable factors to available factors and benefits a fault location method in transmission lines.The fault location method uses the principle of TDOM,which uses the measurement times of double-ends and the velocities of zero-modes.An iteration is necessary for approaching the real fault points.Simulations using PSCAD/EMTDC verify the robustness and accuracy of proposed method.Considering the reality of the large-scale power grid environment,this paper expends the proposed method to implement fault location in complex power grids.Using the proposed algorithm in the power grid first needs to determine the fault lines.Still using the difference between zero mode and line mode propagation on the line,based on the change of the zero-mode traveling wave,the farther away from the point of failure,the longer the time difference between the zero-mode and the line-mode at the same length.According to the phenomenon,a concept of time traversal difference of different modes is defined.The concept of the time traversal difference is used to judge the faulty line.Considering the special circumstances that may exist,such as the fault occurred near the bus,the impact of the line structure on the shortest path of the traveling wave,etc.,a solution is given to ensure the correct choice of the faulty line.In combination with the proposed fault location algorithm,fault location in power grid is achieved.The whole process only needs the arrival time information of the different modes of traveling wave head at measurement points after the fault,and does not require synchronization support.The proposed algorithm is simple,rapid and reliable,and has great engineering application value,which is verified by IEEE-14 and IEEE-30 power system.