The Model of Conductive Interference in Rapid Transit Signaling Systems

With the objective of gaining a complete understanding of conductive interference (CI) in rapid-transit signaling systems, many aspects of the problem have been investigated. This effort has formed part of the Department of Transportation´s Urban Mass Transit Administration (UMTA) rail transit EMI/EMC program and has been conducted in coordination with the UMTA-sponsored Rail Transit EMI Technical Working Group. Topics studied have included dc current-dependent ac impedance of third rail and running rail; circuit properties of the running-rail third-rail circuit from train to substation; statistical signal properties and circuit properties of the multicar train as a source of audio-frequency chopper interference; the coupling of CI currents from rails to track circuit receivers; and field measurements of multicar CI. The result of this program is a complete model of CI that relates CI characteristics of single isolated cars to those of an actual system with multicar trains. Implications of the model for system design are discussed.