EMFRail: A Tool to Calculate Rail Traction Electromagnetic Fields

EMC/EMI is a source of concern from the beginning of planning a new railway line. High powered electrified railways such as HSR are usually AC electrified. This poses a hazard for nearby systems and users. Induced voltages can create electric shock risks or malfunction in signalling or other nearby systems. LRTs, metro lines or commuter systems are usually DC fed and can be located near electromagnetic sensitive equipment such as MRI equipment in hospitals or research equipment — such as electron microscopes — in campuses or laboratories. EMF calculation and impact assessment in early phases of the project rely on simulation and expertise in these complex multi system interrelations. Rail traction creates EM fields which tend to decrease rapidly as the distance from the track axis increases. However, considerations about passengers, workforce and public safety and system compatibility are always needed. As an example, transient currents in DC rail, especially due to short circuits or arcs can interfere with nearby equipment. Even semi steady state DC currents associated with normal operation of the line (traction and breaking currents) present EMC related hazards that need to be assessed in order to evaluate if mitigation measures for associated risks are needed. AECOM’s Madrid Transportation Design Center has developed a tool that provides 3D EMF calculations for railway lines, either AC or DC. This tool, called EMFRail, can deliver EMF estimations based on power load supply simulations considering alignment, separation between tracks, geometry of the electrification system (OCS, third rail), rolling stock mechanical and electric features as well as regenerative braking in order to provide decision support information to make educated project decisions from the beginning of the design. Regenerative braking is a common energy saving tool for railways these days, but has posed new EMF hazards since currents sent back to the OCS can be bigger than those related to traction and this process can occur in different locations of the line (usually when the train is decelerating from maximum speed). This tool can calculate both magnetic and electrical fields for traction frequencies. This tool has been used in several LRT and rail projects providing insightful information to adopt mitigation measures such as underground feeders or operational limitations. EMFRail can simulate mitigation measures for challenging situations such as EMF caused by semi steady state maximum currents (prior to the trip of protection systems). EMFRail can also provide EMF calculations for transmission or distribution power lines once the required current or voltage values (module and phase) are known as well as the position of the different conductors (OCS wires, feeders, rails) of the line under study. EMFRail is developed using MatLab programming suite taking advantage of matrix operation capabilities. Output results are isocurves that can be superimposed to a raised view drawing, 3D contours for specific magnetic field values or even time animated frames to understand worst case scenarios that sometimes are not easy to foresee based on common assumptions.