SHUNTING SENSITIVITY OF TRACK CIRCUITS
This report briefly recalls in the first place the problems entrusted to the Specialists Committee. The report then discusses the theoretical studies and laboratory tests made in order to determine the nature of the physical phenomena concerned and the conclusions deduced from these tests. These studies and tests have been described by the following reports: "Interim Reports" No. 1 of July 1957, No. 4 of November 1958, No. 5 of November 1960 and No. 7 of March 1962. It is emphasized that these investigations have shown that there are sound reasons for replacing the previously customary concept of the "shunt limiting resistance" (that is that greatest ohmic resistance which, when it becomes effective between the rails of an insulated section, is still capable of de-energising the track relay) by the new concept of the "disruptive voltage" or "breakdown voltage", so as to take into account those cases where an insulating layer exists between rail head and tyre, which has to be "broken down" by means of a high voltage. Especially recommended, in order to ensure correct functioning of a track circuit in any possible operating conditions likely to be met, is the high-voltage impulse track circuit, which has been developed by the SNCF and which this Administration uses on non-electrified lines just as much as on line electrified at direct current or at single phase alternating current. This solution, which has been described in Interim Report No. 3 of March 1958, consists in the use of short high-voltage impulses (in the order of magnitude of 100 V during several milliseconds) for feeding the track circuit. It therefore permits the employment of considerable power on the one hand and, because the track is not constantly "live", avoids any danger to the personnel on the other hand. However, the maximum value of the voltage used permits to achieve a break down of even heavily oxidised layers or thick layers of other impurities which may cover the rail surface. Furthermore, the employment of high-frequency track circuits may be mentioned as a recommended solution. The report gives details on the frequencies which are actually used. Furthermore, the report gives an account of the tests made by the FS for the determination of the axle impedance as a function of the frequency. The problem of sanding is likewise dealt with by way of a summary concerning the conclusions in which the many tests made by the SNCF, and partly also those made by the NS, have resulted. The solutions which are to be adopted in practice have been summarized in Interim Report No. 6 of November 1960. Finally, full information is given concerning the question of the functioning of track circuits when passed by vehicles equipped with disc brakes.
- Restrictions on the use of this document are contained in the explanatory material.
International Union of RailwaysOffice of Research and Experiments
- Publication Date: 1962-3
- Pagination: 16 p.
- TRT Terms: Disc brakes; Electromagnetic interference; Track circuits
- Identifier Terms: Ferrovie dello Stato; Societe nationale des chemins de fer francais
- Old TRIS Terms: Question a4
- Subject Areas: Operations and Traffic Management; Railroads; Vehicles and Equipment;
- Accession Number: 00052809
- Record Type: Publication
- Source Agency: International Union of Railways
- Report/Paper Numbers: A4/RF/E Final Rpt.
- Files: TRIS
- Created Date: Jul 8 1994 12:00AM