EMC in railway systems : measurements, modeling and analysis

Abstract: The subject of this study and resulting thesis was to investigate the electromagnetic compatibility (EMC) problems in the multi-electrical signaling circuitry along a railway track. These signaling systems have been expanding over time from buried multi-wired electrical copper cables to optical fiber cables, sometimes located parallel to the contact line in the catenaries. Systems have evolved from simple electromechanical to complex electronic systems and each one of these systems still exists and have to operate together. There intractability has to be faultless, which is unfortunately not always the case. The multi-electrical systems of the railway include the signaling systems along the railway line and security systems, for example point activation mechanism and train indication system. In addition there are detectors measuring the presence of trains, temperature sensors for the points to allow heating during winter, and sensors measuring hot bearings, hot wheels and flat wheels on passing trains. The recent increase in axle pressure from 25 to 30 tons means that higher currents in the rails are now being generated. On top of this, a new generation of trains is being introduced with regenerative electric braking system in the motor, which delivers current back into the system when slowing down the train. This makes it important to have resistant systems close to the railway environment. The systems has to have a robust construction and last over a long period of time with consideration to externally applied fields and influences of weather conditions. The location of the different systems can also be far from support, maintenance, and service. To investigate the problem of radiated and conducted electromagnetic (EM) interference, it was necessary to develop measuring methods. Measurements have been done to find out if the more sensitive systems are influenced by higher voltage systems in the signaling circuitry. An existing EM modeling tool was utilized, to model crosstalk between rails and contact lines, and modified to incorporate a combination of two- and three- dimensional models for reduced time and space complexity. The resulting simulation environment can be used to analyze possible sources of EM disturbances in the multi-electrical signaling circuitry as it is today, and to reduce the sources that generate problems. This gives a new application of the measurement method and further development of a simulation tool. One of the objectives in this project is to find out the tolerance of the low voltage detector systems in the presence of higher voltage system used in the railways. One of the conclusions is that correct installation is important and failure to comply with installation procedures results in high EM interference.