Research On An Automatic Fault Isolation Method In High Speed Railway 10kV Power Transmission Line

Until January 2016, the length of China high-speed railway has covered a distance of 19 thousand kilometers, making up 60% of the total railway distance of the world. China high-speed railway has the longest operation length, the largest construction scale, and the busiest management, making it essential to guarantee the high-speed railway in safe and stable operation. lOkV power transmission line provides power supply for railway station, communication signals along line, and other non-traction electrical equipment. It features long distance, massive load connection, adverse geological conditions, and high chance of fault event. It requires the fault section be quickly and accurately isolated, and the power supply of non-fault section be quickly restored to keep the railway in safe and reliable operation. However, current relay protection and isolation schemes for high-speed railway power transmission lines are not selective. For example, existing protection device is only installed at the head end of the line. Once fault occurs at any location of the line, the protection trip will cut off the power supply of the whole line, which causes a wide range of damage and affects the efficiency of fault location and power restoration. Therefore, this paper proposed a novel fault section isolation scheme for lOkV power transmission line. According to the scheme, the fault of the transmission line can be quickly identified, then fault section is isolated and the power supply of non-fault section quickly recovers. It avoids the power loss of non-fault section resulted from manual switching actions, and significantly improves the reliability of power supply of railway power transmission line. The main contributions of this paper are summarized as follows:(1) Modeling and fault characteristic analysis of lOkV power transmission line of high-speed railway. Based on the basic structure, operation mode, and neutral point grounding mode of the railway power transmission line, a simulation model of the power transmission line was built on MATLAB/SIMULINK platform according to the practical parameters of power source, voltage regulator, cables, and loading in a high-speed railway. The models can accurately reflect the fault characteristic of electrical quantities under different operation conditions, providing basis to put forward and verify the fault section isolation schemes.(2) A fault section isolation scheme independent of communication for power transmission line was presented based on non-communication protection principles of the distribution lines. The protection device is only installed at the distribution substation in traditional lOkV power transmission line, while in this paper, we consider to deploy additional protection devices to the box transformers along line. With fault information of the lines, when the breaker of the box transformer trips first, the breaker at the other side trips subsequently based on the secondary disturbance information of the variations of power frequency quantity. Based on the premise that previous time coordination is not affected, single-terminal fault location algorithm is applied to accelerate protection action time, and the isolation time of fault section is further reduced. The proposed method can cut off fault section from both sides, ensuring the rapidity and selectivity of fault isolation.(3) The automatic fault isolation scheme for power transmission line presented in this paper can isolate most faults, while it lacks selectivity for symmetric faults. Therefore, a fault section location and isolation scheme for power transmission line based on communication was put forward by utilizing original SCADA communication channels. According to the characteristics that the directions of the zero-sequence current at two ends of the fault section are opposite, while those of the non-fault section are identical, firstly a fault section location method for power transmission line was proposed. This method only utilizes the zero-sequence current of each measuring point to achieve fast location of the fault section, and can avoid the influence of fault distance, distribution transformer loading, and transition resistance. According to fault section location result, the box transformer protection of both sides of the fault section is activated based on communication. Both symmetric and asymmetric fault can be automatically isolated quickly, therefore the power-loss area is reduced and power supply reliability is improved.(4) Aiming at the fault section isolation schemes under both non-communication conditions and communication conditions, corresponding automatic put-in schemes of standby power source were presented, and the power supply of non-fault area is fast restored after fault occurs. Then a complete automatic fault processing system for railway power transmission line was designed, which works under both communication conditions and non-communication conditions. When fault occurs, the system quickly and accurately cut off the fault section, and the non-fault section restores normal operation to guarantee the stability and reliability of railway power transmission line..