Track vacancy detection system
The train detection system , being a part of the grounds of a signal box to the signal system of a railroad. Its purpose is to determine that the individual sections of the route of a train are free before the main signal is set . In addition, the change of the vacant and occupied display in relay interlockings and electronic interlockings controls all essential functions of the interlocking when setting, securing and clearing the routes and when setting the signals. The vacancy of the individual guideway elements as well as the occupancy is indicated by detectors in the schematically shown track diagram on a table or monitor.
A train detection system, which in a track of the free section is incorporated is called track track-free signaling system . Automatic route blocks cannot be implemented without them.
Route sections that are equipped with a track vacancy detection system are called vacancy detection sections . The track sections of the train station and the free route as well as the switches and crossings in the route, which have a common track vacancy detection, each form a vacancy detection section. For example, adjacent switches or a switch together with the track section adjoining them often form a vacancy detection section.
The following three systems are used in Germany:
- Track circuits,
- Audio frequency track circuits and
- Axle counting circles.
Deutsche Bahn assumes an average operating time between failures of track vacancy detection systems (including their interface) of 219,000 hours and an average downtime (MDT) of two hours.
Track circuit
function
A track circuit works together with a track section in which the two rails are isolated from one another (consequently at least one of the two from earth ). Depending on the manufacturer, an electrical voltage of 1 V to 4 V is applied between the rails (closed- circuit current principle ). Due to the otherwise possible interference of the third harmonic of the drive return current on electrified routes in the 15 kV network, but also on non-electrified routes, the frequency is 100 Hz or 42 Hz. Until the introduction of general electrical heating of passenger trains, non-electrified routes were also used the easily provided frequency of 50 Hz is used. As long as the circuit consisting of a series resistor, insulated rail, separate cable route to the winding of the track relay and back is not interrupted or short-circuited, this relay picks up and the track vacancy detection system shows the unoccupied state. If the circuit is short-circuited to the other rail via the wheel sets of a rail vehicle or - z. B. due to a technical fault - interrupted or there is a discharge due to insufficient bedding resistance, the voltage on the track relay breaks down, it drops and the track vacancy detection system reports the occupancy. In addition, track circuits enable conditional rail break monitoring. The isolated strings are connected in series within a section .
In the case of single-rail insulated track circuits, the insulated rail must be interrupted at both ends. At the separation points, it is connected to the following track section with what is known as an insulating joint. The phase sequence of the supply to the individual sections must be selected so that if an insulation joint fails, none of the track relays involved can pick up due to the supply voltage of the neighboring section. The safest way to do this is to change the insulated rail at each of these transitions. This means that each isolated strand is adjacent to an earthed one. The earth rails are connected to one another at these insulating joints using diagonal or Z-connectors. It is disadvantageous that the isolated strand cannot be used for the return current flow in the case of electrical traction. In order to be able to use the full cross-section of both rails for this purpose, long insulation sections in particular are double-rail insulated in line and continuous main tracks and equipped with impulse transformers. A choke surge transformer contains a low-resistance low-voltage winding with a large cross-section and center tap and a high-voltage winding with many turns. The reverse current flows through both parts of the low-voltage winding bifilar and therefore has no effect on the track vacancy detection; A simple transformer is used for the free signaling current, which is fed in via the high-voltage winding on the supply side and taken from the relay side . Double-rail insulated track circuits are only used in track sections, but not in switches and crossings.
To ensure the highest possible level of safety, a three-phase system is used for the track circuits . One of the phases is applied to the rail . A three-phase asynchronous motor that works against a spring is used on the receiver side for evaluation. In order for this so-called motor relay to leave the basic position, one or both of the other phases directly taken from the three-phase network are necessary in addition to the phase taken from the rail, depending on the design. With two-phase supply, the phase shift between the control and auxiliary phases should be 90 °. Two adjacent track sections may not use the same phase. In this way it is prevented that a current fed in from the neighboring track section is evaluated via an insulation joint bridged due to a fault - the current would flow through the winding of the motor relay, but due to the incorrect phase position the motor cannot deliver sufficient torque to counteract the Spring to work.
As a side effect, it is possible to change the direction of rotation of the motor relay by reversing the polarity on the feed side of the track circuit. In this way, in older self-blocking systems, the information about the position of the main signal is transmitted to the previous block or exit signal .
advantages
Track circuits offer immediate monitoring of freedom. The entry and exit of road-rail vehicles is recognized as well as vehicles standing on the track, e.g. B. after construction work. Since there is no axle counting due to the system, counting errors cannot occur in the first place.
disadvantage
Wrong busy message
Track circuits are sensitive to soiled bedding and changing weather conditions. So z. B. Rainwater in connection with cargo residues (especially salts) lower the bedding resistance so much that the track relay drops out and triggers an occupancy indicator.
In addition, the insulation joints are mechanically relatively sensitive and a foreign body in the gapless track. A glued insulating joint behaves like a normal rail profile when it is new, but the gluing can come off due to the load changes when driving on it. If the intermediate insulating layer breaks out between the two rail profiles, the rail heads can close the insulating gap by rolling over them and also lead to incorrect red illumination. Both errors work on the safe side, however.
Wrong vacancy report
False clearance reports are dangerous. One possible cause for this is the disruption of the electrical contact between the wheel sets and the rail due to sand or rust. Therefore, a minimum number of axes running over them is required within 24 hours. If this is not achieved, the section concerned must be checked in another way to ensure that it is clear before the next journey is permitted. However, the problem can be avoided with little effort by a corresponding timetable construction; it practically does not occur on main and main tracks that are regularly used.
Sand on the rails caused critical situations several times, most recently in a near-accident in Mainz on August 1, 2013 . The Federal Railway Authority has therefore set up rules for the use of the sand spreading device in several general decrees, according to which sanding is prohibited at speeds below 25 km / h except in the event of operational danger. If it happened anyway, the driver has to notify the dispatcher immediately .
In principle, track circuits do not recognize derailed wagons.
Audio frequency track circuit
An audio frequency track circuit works on the same principle as a track circuit. Here, however, instead of the closed circuit, the rail is energized from one side via a transmitter , which is modulated with an audio signal with a frequency of 9,500 Hz or alternatively 14,500 Hz, which is picked up by a receiver on the other side. Occupying the vacancy detection section with a rail vehicle leads to a disruption of the audio signal and thus generates the occupancy indication of the track vacancy detection system.
In contrast to the track circuits, the ends of the audio frequency track circuits do not have to be galvanically isolated from one another. The separation of the neighboring track sections is realized by applying different frequencies in these track sections and special resonance circuits at the ends of the sections. This arrangement, also known as S-connector , enables the separation to be relatively imprecise - in switch areas where an exact separation of the adjacent track sections is necessary, insulating joints are therefore usually required even with audio frequency track circuits.
With modern audio-frequency track circuits, information can also be transmitted from the route to the locomotive via various types of modulation . This is used in various train control systems , for example the TVM used on French high-speed lines.
A faulty audio frequency track circuit resulted in a serious accident at Metro Washington in 2009 with nine fatalities and many injuries. Here, the audio frequency signal from the transmitter was coupled directly into the receiver via the heat sink, the metal structure of the racks and the shared power supply, so that the receiver detected the audio signal, which led to the cover signal being set even though the track was still occupied.
Axle counting circle
An axle counting circuit works on a completely different principle. It uses contact-free electromagnetic pulse generators , also known as axle counters , which, depending on the type, are attached to the outside and inside or only to the inside of the rails at the beginning and end of a vacancy reporting section. Each wheel on one side of the axles of the rail vehicles generates an electrical pulse when passing the pulse generator, which is recorded and processed by a motor-driven or electronically operating counter . By arranging two pulse generators a short distance apart, often in a common housing, the direction of travel can also be determined. The track vacancy detection system only reports vacant if the status of both counters at the beginning and the end of the vacancy detection section is the same ; every difference between the two counters generates an occupancy display.
Due to the sensitivity of track circuits to interference, axle counting circuits are mainly used in new buildings in Germany today. Axle counters and their components are practically wear-free and overall function more reliably than track circuits. However, they work with active electronics that require maintenance and are more expensive to purchase. A disadvantage of axle counters is that they only indirectly check whether the track is clear, the condition of the system can change unnoticed in the event of a malfunction and therefore a manual check for clearness is necessary after a malfunction.
Since axle counters can also be installed on tracks equipped with track circuits without the two vacancy detection systems influencing each other, systems of the type that are not yet available are often installed during conversions.
Modern axle counting systems, so-called multi-range axle counters, can compensate for individual counting errors by not only using the two limiting counting points to report a section as free. If 24 axes enter at the first counting point, at the next counting point only 23 axes are recognized due to an error, but 24 axes are reported again from the next but one and the following counting point, both sections can be reset to the basic state. However, this procedure is not permitted in the area of Deutsche Bahn. In practice, therefore, the first section remains occupied because there is still one axle in the section, and the second section is faulty because more axles are extended than retracted.
ETCS level 3
With ETCS Level 3 , the track vacancy is reported via position reports from the trains, which contain completeness reports on the vehicle. The ETCS center (RBC) transfers the vacancy information to the respective interlocking.
Mixed forms, in which larger, conventionally cleared sections are divided into smaller, “virtual” sections, cleared by the train, are possible and are referred to as “ETCS Level 3 Hybrid” or “ETCS Level 2 HD”. Such a mixed form is used, for example, in the Wuppertal suspension railway .
literature
- Wolfgang Fenner, Peter Naumann, Jochen Trinckauf: Railway safety technology: controlling, securing and monitoring of routes and speeds in rail traffic. Wiley, 2011, ISBN 978-3-89578-683-9 , limited preview in Google Book Search.
- Basic knowledge of the railway. 6th edition. Verlag Europa-Lehrmittel , Haan-Gruiten 2012, ISBN 978-3-8085-7423-2 .
Web links
Individual evidence
- ↑ Study on the introduction of ETCS in the core network of the Stuttgart S-Bahn. (PDF) Final report. WSP Infrastructure Engineering, NEXTRAIL, quattron management consulting, VIA Consulting & Development GmbH, Railistics, January 30, 2019, p. 269 , accessed on April 28, 2019 .
- ↑ a b Wolfgang Fenner , Peter Naumann, Jochen Trinckauf . Railway safety technology: controlling, securing and monitoring of routes and speeds in rail traffic. 2nd edition Publicis Corporate Publishing, Erlangen 2003, ISBN 3-89578-177-0 .
- ↑ See justification of August 12, 2013 on the general ruling of August 8, 2013 ( Memento of December 27, 2013 in the Internet Archive ), website of the Federal Railway Authority
- ↑ Authority warns against the use of sand on rails. In: The world . January 3, 2013.
- ↑ General decree of August 8, 2013 ( memento of December 27, 2013 in the Internet Archive ), PDF file on the Federal Railway Authority's website
- ↑ Safety Recommendation on the Washington metro disaster. (PDF; 88 kB) (No longer available online.) National Transportation Safety Board Washington, September 22, 2009, archived from the original on January 3, 2015 ; Retrieved January 3, 2015 .