A Method of Faulty Section Location Based on Algebraic Sum of Feeder Current Fault Component

When a positive pole grounding fault (PPGF) occurs in a certain zone of the straddle-type monorail (STM) DC traction system (DCTS), this causes multiple 64D grounding protections to activate and the circuit breaker of the DC feeder to trip. The protection loses selectivity and leads to a large-area power outage of the DCTS. It is necessary to locate the fault zone as soon as possible in order to reduce the impact of the accident. Firstly, this paper analyzes the simplified equivalent model of the DCTS fault component in case of PPGF and the equivalent model of DCTS in case of sudden entry of a locomotive. Secondly, it analyzes characteristic differences in the magnitude of the algebraic sum of fault current components (M-ASFCC) for the locomotive-free area, faulty area, and locomotive area based on the above two equivalent models, respectively. Then, it derives the characteristic differences in M-ASFCC of the three types of sections when PPGF occurs simultaneously with the sudden entry of the locomotive according to the law of superposition. After that, the faulty section location (FSL) method was proposed based on the feeder algebraic sum of fault current components (ASFCC). It should be noted that the theoretical derivation of the proposed method is based on a linearized small-signal approximation at the fault instant. The constant-power locomotive load with power electronic converters is approximated as a fixed impedance, which is only valid under minor voltage disturbance at the moment of fault inception. If the M-ASFCC of a zone in the DCTS exceeds the setting value, the zone is judged to be faulty; otherwise, it is identified as normal. Finally, the proposed method is verified by MATLAB R2019b simulations that can locate the fault section quickly and accurately, which lays a good foundation for subsequent fault processing. Compared to other methods, the method has higher protection sensitivity and can withstand larger transition resistance (TR).