Research On Traveling Wave Fault Location Method For Complex Transmission Lines Based On Distributed Current Measurement

Transmission line is an important facility connecting the power plant and the user side of the power system.The traditional fault location method of transmission line traveling wave is based on the three-phase voltage and current signal in the line-end substations,and the location of fault point is calculated according to the time when the traveling wave arrives at each substation.For faults occurring in complex transmission lines such as multi-terminal lines and overhead line-cable hybrid lines,the conventional traveling wave method is difficult to accurately identify the line from the fault point due to the occurrence of wave reflection and wave velocity mutation at impedance discontinuous points.To solve the problems aforementioned,the current-wave propagation behaviors in complex transmission lines is studied in this paper,the transient current sensor based on load current coupling is developed.The relevant algorithms and devices have been verified in actual enginerrings.The main work and achievements are as follows:The reflection and refraction law of current waves in dual-power transmission line is studied,and a method to calculate the location of fault points using midpoint current is presented.A method to identify the faulty interval based on the deviation degree of the fundamental current wave at both ends of the line and the energy of the transient wavefront is proposed in this paper.Furthermore,according to the calculated value of wave velocity of current wave in overhead line derived from line parameters,the accurate time of reflected traveling wave from the end of transmission line arriving at the middle point of line is obtained by analyzing the length of transmission line and the time of initial traveling wave arriving at the middle point of line,and finally the exact location of fault is obtained.This method does not need time synchronization,eliminates the error between the calculated value of wave velocity and the real value,eliminates the interference of false root,improves the accuracy of fault location,and the correctness of this algorithm is verified through simulation.The fault current traveling wave has different propagation speeds in the overhead line and the cable,and the characteristic impedance is discontinuous on different sides of the line-cable connection point.This paper analyzes the law of refraction and reflection of the current wave passing through the joint point,and divides the mixed transmission line into three fault location intervals.According to the characteristics of the traveling wave propagation network of the fault point at different positions,combined with the polarity law of the wavefront after multiple reflections,the faulty interval is determined.Based on the information of the faulty interval,the recorded data in the corresponding current sensor is extracted,the true propagation speed of the traveling wave in the overhead line and the cable can be calculated,and finally the exact position of the fault is obtained.Multi-terminal transmission lines are common in the medium-low voltage distribution network.It has the characteristics of complex network structure,short length of each branch line,and large randomness of the fault.In this paper,the complex topology of the multi-terminal transmission line is simplified into several fault location intervals,the time instants of the initial traveling wave passing through the midpoint of each branch line is taken as the analysis object,and the specific faulty branch is determined by comparing the calculation value of the traveling wave velocity.The recorded current wave data in the distributed current sensor mounted at the midpoint of the branch is applied as the analysis object,and the precise wave velocity and the true position of the fault point can be obtained.Time synchronization is not required.The hardware cost is reduced while improving the positioning accuracy,and the positioning step is simplified.A distributed current measuring platform for fault location applications in complex transmission lines has been developed.The platform is installed on the overhead transmission line with load,it is powered by load current coupling together with backup battery,and the broadband Rogowski coil is used to obtain the high-frequency post-fault transient current wave.Considering that the energy conversion of current coupling is relatively low,the data acquisition card cannot work in the high-frequency sampling mode for a long time,so the intelligent dual-frequency switching function is designed in the device.The distributed current-measuring-based fault location method for complex transmission lines is completed depending on the theoretical research results and hardware platform I developed aforementioned.The new method is verified in actual enginerrings.The results show that the test results are consistent with the theoretical analysis.