Research On Single-pole-to-ground Fault Protection Scheme Of Fourth-rail Traction Power Supply System

Urban rail transit has the advantages of convenient travel,environmental protection,green,high operating efficiency,and strong transport capacity.As an important means of transportation,subway has become the preferred transportation choice for many citizens.The fourth-rail traction power supply system adopts the power supply method of contact rail power supply and return rail backflow.The return rail replaces the steel rail backflow,eliminating stray current from the root cause,and completely solving the problem of corrosion of stray current.At present,there are still some problems that need to be solved in the relay protection research of the fourth-rail traction power supply system.This paper conducts an in-depth study on the single-pole-to-ground fault of the fourth-rail traction power supply system and proposes a corresponding relay protection scheme,which can quickly detect and remove the faulty section,reduce the power outage range,and reduce the fault loss.Firstly,the fault analysis of the single-pole-to-ground fault is carried out,and the fault circuit is equivalent by superimposing the load component circuit and the fault component circuit;the model of the fault component circuit is derived and structure is simplified from two aspects: positive-to-ground fault and negative-to-ground fault;Based on the simplified fault component circuit,the fault component current distribution is studied,and the fault section and non-fault section are distinguished by comparing and analyzing the fault component currents on both sides of the fault section and non-fault section;and the variation rules of the fault component current under different transition resistances are analyzed.Then,this paper proposes current differential protection as the main protection method;analyzes the error of the current measuring device;analyzes the synchronization method of the sampled value;and distinguishes positive-to-ground fault and negative-to-ground fault by fault pole judgment;and proposes transducer disconnection self-checking schemes respectively,aiming at current transducer and voltage transducer disconnection;the singlepole-to-ground fault protection scheme is designed from the aspects of hardware structure and program design.Finally,the simulation model of the fourth-rail traction power supply system is built on the Matlab/Simulink simulation platform,and the protection scheme is simulated and verified from four aspects: different fault poles,different transition resistances,current transducer disconnection and voltage transducer disconnection.