scholarly journals Increase of metro line capacity by optimisation of track circuit length and location: In a distance to go system

2010 ◽  
Vol 44 (2) ◽  
pp. 53-71 ◽  
Author(s):  
J. Gonzalez ◽  
C. Rodriguez ◽  
J. Blanquer ◽  
J. M. Mera ◽  
E. Castellote ◽  
...  
Keyword(s):  
Track Circuit ◽  
Circuit Length

Assessment of Broken Rail Protection in Audio Frequency Track Circuits

2014 ◽  
Author(s):  
Joseph W. Schaad
Keyword(s):  
Formal Method ◽  
Mathematical Methods ◽  
Operational Characteristics ◽  
Track Circuits ◽  
Track Circuit ◽  
Impedance Calculation ◽  
To Receive ◽  
Circuit Length ◽  
Normal Track

In addition to the vital function of train detection, a track circuit is also expected to provide an indication of a broken rail within its boundaries. Ability to detect a broken rail in a double rail track circuit is a result of the failsafe design principle, which interrupts the flow of track signal current and drops the track relay in the presence of any credible component failure. The overall result of such an event is identical to that of track occupancy, which causes the associated signals to be set to the most restrictive aspect. In the case of electrified territory, the ability to detect a broken rail may be compromised by the presence of crossbonds between parallel tracks. These additional connections, which are intended to minimize potential differences in the negative return system, also provide a sneak path for track signal current to flow from transmit to receive ends of the track circuit under broken rail conditions. In most cases involving 2 parallel tracks, application of a simple rule of thumb (described in this paper) regarding crossbond spacing and track circuit length is sufficient to ensure broken rail protection. In situations which are marginal, or where complex track work is involved, a more detailed analysis is necessary. Evaluation of the broken rail protection in such cases requires that the sneak path impedance be calculated and compared to the normal track circuit impedance. A formal method for this impedance calculation, based upon the classical circuit analysis techniques, is presented. To completely characterize the behavior of the track circuit under broken rail conditions, the operational characteristics of the track circuit must also be considered. In this paper a digital jointless AF track circuit, operating in the 9.5–20.7 kHz range, is used as a basis for this discussion. The operational characteristics of the S-bond, O-bond, as well as the role of overdrive are considered in the context of broken rail (BR) protection. The mathematical methods described for the simplified examples in this paper can readily be expanded to include any number of parallel tracks.

The Effect of Friction Modifiers on Wheel/Rail Isolation

2008 ◽  
Author(s):  
E. A. Gallardo Hernandez ◽  
J. Cotter ◽  
R. Lewis ◽  
D. T. Eadie
Keyword(s):  
Input Voltage ◽  
Electrical Circuit ◽  
Friction Modifiers ◽  
Friction Modifier ◽  
Contact Impedance ◽  
Static Tests ◽  
Railway Systems ◽  
Significant Difference ◽  
Track Circuit ◽  
The Impact

Train detection, for signalling purposes, is often by means of track circuits. Signalling block occupancy is triggered by the wheelset of the train ‘shorting out’ the track circuit, i.e. the wheels and axle act as a shunt. Contamination on the track such as ballast dust, rust, oil, or leaves as well as substances designed to improve train operation such as friction modifiers or sand may cause the contact between the wheelsets and the track to be compromised, inhibiting train identification. In previous work a twin disc approach has been used to study the effect of sand (used to improve adhesion) and leaves on wheel/rail isolation. Friction modifiers are of significant current interest in wheel/rail research. Introducing a new material into the tread/top of rail interface can raise questions about the impact on signalling systems. Although no significant effects have been observed in practical operation on a range of railway systems, the intention in this work was to evaluate conductance between wheel and rail in a more controlled and systematic fashion using the previously established methodology. Using the twin disc technique, friction modifier, in the form of a solid stick, was applied using a spring loaded device to the rotating wheel disc to generate a visible film. Tests were run to measure contact impedance at typical loads and slips. Static tests were also carried out using discs pre-conditioned with a friction modifier film. The electrical circuit used was a modified simplified simulation of audio frequency track circuit. No significant difference was observed in the measured impedance for dry conditions with no friction modifier, versus tests where friction modifier was applied, regardless of percentage slip or input voltage. The analysis suggests that the introduction of friction modifier into the existing wheel/rail interfacial film does not result in increased impedance with all other factors being equal.

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