United States Department of Transportation
i
Inductive Interference in Rapid Transit Signaling Systems Volume I: Theory and Background
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1986-05-01
[PDF-1.61 MB]
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Abstract:This report describes the mechanism of inductive interference to audio frequency (AF) signaling systems used in rail transit operations, caused by rail transit vehicles with chopper propulsion control. Choppers are switching circuits composed of high-power semiconductor devices, inductors, and capacitors. Chopper-controlled propulsion systems on subway cars can cause inductive interference with AF signaling systems, when time-varying magnetic flux lines emanating from chopper systems on vehicles pass through the rail-axle loops under the cars. When a vehicle passes over points at which track circuit receivers are connected to the rails, inductively generated interfering signals can cause track circuits to malfunction. Observation of such interference led directly to the establishment of the Rail Transit EMI Technical Working Group, under the sponsorship of the Urban Mass Transportation Administration. This report also examines chopper interference generation as well as methods for observing and recording interference signals; develops a physical model for calculating levels of inductive interference; gives selected results of field observations; and discusses methods for alleviating the problem, such as improved track signal detection, frequency-domain coding, and new chopper components that generate less stray flux.
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