Research On Fault Location Methods For City DC Railway Traction System

With the development of economy and society, urban rail transit has become one of the main public transport in more and more cities. Due to the increase of lines and the traffic density, higher requirement has been put forward to the safety and reliability of urban rail transit power supply system. The power grid provide electricity to the locomotive by power supply system, which operates under harsh conditions and without reserve. In order to enhance the reliability of metro power supply system, improvements can be considered from two aspects. On the one hand, a more reliable protection algorithm should be designed so as to reduce or eliminate protection mal-operation. On the other hand, fault location techniques are needed, which can estimate the fault location and help to speed up the repair process after fault clearance by the protection devices. At present, mature fault location methods or devices for DC traction power supply system have not yet been put into practical application. The traditional way of manual patrol is not good enough nowadays taking the time and cost into account. This paper focused on the fault location methods for DC railway traction system to ensure safe and reliable operation of the power supply system.Firstly, this paper studied the structure, parameters, operation and fault feature of the DC traction power supply system in-depth, and put forward an improved algorithm using steady-state electrical parameters based on the impedance method. To improve the accuracy and avoid the impact of transition resistance to fault location results, a double-ended differential time-domain algorithm solved by the least square method was presented. In the case of the subway substations do not have communication condition, an improved single-ended fault location algorithm on the basis of double-ended differential time-domain algorithm is further proposed, through constructing optimization function and solved by genetic algorithm to get the fault location. Modeling based on Matlab/Simulink according to an actual metro power supply system parameters, through fault simulation analysis to verify the feasibility of the algorithm, and the measured data of Shenzhen metro were used to prove the practicability and accuracy of the algorithm.Reference to the traveling wave method which is commonly used in high voltage DC transmission line fault location, this paper analyzed the applicability of traveling wave method in the DC railway fault location. Based on the existing transmission line traveling wave fault location principle, an accurate fault locating method based on single terminal travelling wave avoids the influence of wave speed was presented. Choose the wavelet transform in travelling wave analysis and fault feature extraction, and get the exact arrival time of travelling wave based on wavelet modulus maximum principle.At last, due to the two common methods applied in fault location, the travelling wave method and the failure analysis method have advantages and disadvantages in different conditions. This paper combines the two algorithms of complementary advantages, which can use the fault transient information of time domain without the need of time-frequency conversion and the data window is short. Therefore, the accuracy can be guaranteed and locating quickly and accurately at the same time. The combination algorithm isn’t affected by the distance, fault type and transition resistance through simulation tests, that verified the high fault location accuracy and strong robustness.