Study On Spectrum Characteristics Of Metro Rail Mutual Impedance And Its Application In Transition Resistance Detection

Metro adopts DC power supply mode,and rail acts as return rail at the same time.Because rail can not be completely insulated to the ground,stray current will flow into underground.Stray current will not only damage reinforced concrete,but also corrode buried pipelines.Because stray current is not easy to measure,and transition resistance is the main factor affecting stray current,so it is more intuitive and feasible to measure rail-to-ground transition resistance.At present,the off-line method is mostly used to measure the rail-to-ground transition resistance,which has large workload and low accuracy.Therefore,it is necessary to explore a new method for measuring transition resistance.This paper studies the metro rail model needed to study the spectrum characteristics by CDEGS,explores the errors caused by rail length,rail type and number of segments in the model to the simulation results,analyses the variation law of simulation results errors caused by different parameters in the model,and finally gives the simulation model of rail mutual impedance spectrum characteristics.It is proposed that when the rail length exceeds 10 km,the rail length will no longer cause errors in the spectrum characteristics of mutual impedance.When the segment length of the model is less than 50 m,it can be considered that the rail length will no longer cause errors in the spectrum characteristics of mutual impedance below 1MHz.Then,on the basis of the established rail model,the effects of structural steel bar resistance,drainage network resistance,soil resistivity and transition resistance on the spectrum characteristics of rail mutual impedance are simulated and studied.The results show that: compared with the low frequency and high frequency stages,the mutual impedance modulus in the intermediate frequency stage is more sensitive to the longitudinal resistance of the structural steel bars;the influence law of the drainage network resistance is similar to that of the structural steel bars resistance,but different from that of the structural steel bars in the low frequency stage;the influence of the soil resistivity on the spectrum characteristics of the rail mutual impedance is mainly over 800Hz;The spectrum characteristics of rail mutual impedance are mainly between 50 Hz and 400 KHz.Finally,this paper studies the non-uniform distribution of the transition resistance in the common section in practice,and focuses on the influence of the amplitude and position of the transition resistance in the non-uniform section on the frequency characteristics of rail mutual impedance,and compares and analyses the difference between the transition resistance and other influencing factors on the frequency characteristics of mutual impedance.It is found that the transition resistance is different from the frequency band affected by other factors.Using this difference to select the appropriate frequency band can exclude the influence of other factors on the spectrum characteristics of mutual impedance,and the ratio method can be used to roughly determine the range of the transition resistance.The modeling method of the simulation model of rail spectrum characteristics in this paper provides a new idea for the study of rail mutual impedance spectrum characteristics and transition resistance,and can be used for the detection of rail to ground transition resistance.