Research On Groungding Circulating Current Of 27.5kV Feeder Cable For High-speed Railway

With the rapid development of railway construction,the application of 27.5k V high-voltage single-core cables as traction feeder cables in electrified railways has become more and more common.The traction substation and the traction contact network need to be connected through a traction feeder cable.Therefore,ensuring the normal operation of the traction feeder cable is of great significance to the entire traction power supply system.The method of judging the insulation state of the cable by detecting the cable grounding circulation has been recognized and applied in the conventional power system.The core point of this scheme is to confirm a threshold for judging the insulation state of the cable.The threshold used is calculated based on the rated current.However,the common VCB operating overvoltages and locomotive harmonics in the railway system will increase the amplitude of the cable grounding circulating current.If the above method is used to calculate the threshold value,it will cause the staff to misjudge the cable insulation status.Therefore,it is necessary to study the influence of VCB operating overvoltage and locomotive harmonics on cable grounding circulating current in order to provide a data basis for the application of cable grounding circulating current detection in railway systems.This thesis combines the actual use of the traction feeder cable in the railway AT power supply system,and analyzes the generation mechanism of the cable grounding circulating current and its main influencing factors.Then using PSCAD/EMTDC electromagnetic transient simulation software,a simulation model of the traction feeder cable is established.The simulation analyzes the influence of the time-domain and frequency-domain information of the core current on the cable grounding current.On this basis,a cable grounding circulation test is carried out to verify the simulation results.In order to analyze the influence of VCB operating overvoltage and locomotive harmonics on the ground circulation of traction feeder cables,PSCAD/EMTDC was also used to establish a simulation model for VCB operating overvoltages and locomotive harmonics.Two aspects of the domain verify the accuracy of the simulation model.Finally,through the joint simulation of the VCB operating overvoltage model and the locomotive harmonic model with the cable model,the influence of these two working conditions on the cable grounding circulation is obtained.The research results show that: VCB operating overvoltage and locomotive harmonics will cause an increase in the ground circulating current of the traction feeder cable.The difference is that the grounding circulating current under the influence of the VCB operating overvoltage has a high-frequency component dominated by 800 k Hz,which makes the relationship between the cable length and the grounding circulating current appear to be approximately sinusoidal.Therefore,it is necessary to know the specific length of the cable used in actual application.In summary,the research helps to confirm the cable grounding circulating current threshold required to judge the cable insulation status.