Study On The Electromagnetic Interference Between High-voltage AC Overhead Transmission Lines And Railway Communication Signal System

With the rapid development of our social economy,the mileages of new railway,reconstruction and expansion railway have all increased continuously in our country.At the same time,high-voltage transmission lines are becoming more and more crowed because of the increasing demand for electricity.As a consequence,the crossing or paralleling between high-voltage transmission lines and railway has happened regularly in recent years.The electromagnetic fields surrounding high-voltage transmission lines have becomed a threat to the safe operation of railway signal system.One of the railway signal transmission ways is signal cable transmission.The electromagnetic interference from high-voltage AC overhead transmission lines(HOTL)to signals transmitted by cable can be evaluated by induced electromotive force(IEF)in signal cable.This paper combed the theoretic calculation methods of the IEF which was caused by HOTL.On this basis,employing CDEGS software,this study simulated the electromagnetic interference from 500kV HOTL to signals transmitted by cable under normal operating or fault condition(single-phase grounding fault).Meanwhile,changing single parameter(a total of 10 parameters,including parameters of HOTL and signal cable,as well as their positional relationship),the IEF in the core and sheath of the railway signal cable were calculated to analyze the influences of this parameter on electromagnetic interference degree.The results showed that for the single-circuit HOTL arranged in horizontal or triangular,the IEF in the core and sheath of the signal cable caused by the former was larger than the latter.For the double-circuit HOTL arranged in positive or negative phase sequence,the IEF caused by the former was larger than the latter.The IEF in the core and sheath of the signal cable caused by the HOTL could be effectively reduced by increasing the crossing angle,horizontal distance between HOTL and signal cable,increasing the height of HOTL and reducing parallel length of HOTL and signal cable.The second way of railway signal transmission is radio transmission.The electromagnetic interference from HOTL to signals transmitted by radio can be measured by radio interference intensity(RII)above ground 1.5m.In this paper,the theoretic calculation methods of RII above ground 1.5m were summarized.Moreover,combined with 500kV Ying River 5360 HOTL,the differences in power frequency electric field,magnetic field and radio interference surrounding HOTL between actual measurements and predicted values of Enviro module of CDEGS software were analyzed.It was verified that predicting electric field,magnetic field and radio interference of HOTL by Enviro module of CDEGS software was feasible.Based on this,Enviro module of CDEGS software was used to simulate the radio interference from 500kV HOTL to signals transmitted by radio.Meanwhile,changing single parameter(a total of 9 parameters,including parameters of HOTL,soil resistivity and weather conditions),the RII above ground 1.5m,as well as the intensity of power frequency electric and magnetic fields were calculated to analyze the influences of this parameter on radio interference degree.The results showed that the maximum RII produced by single-circuit HOTL arranged in horizontal was as great as that produced by single-circuit HOTL arranged in triangular.However,the latter declined more slowly in the direction which was perpendicular to the HOTL.The RII above ground 1.5m caused by the HOTL could be effectively lowered by increasing phase spacing and height of HOTL,separated numbers of conductors and cross-sectional area of sub-conductors,and reducing separated space of conductors.