media_Whitepaper_Gleisstromkreis - Track circuits versus wheel detection.pdf

Wheel detection and axle counting systems provide the basic informa-tion for track vacancy detection, for controlling level crossing systems and a range of switching tasks or trigger functions. This technology is established throughout the world for standard gauge railways and is increasingly replacing track circuits.

The requirements and the framework conditions in rail-based public transportation systems do, however, differ significantly from those in the standard-gauge railway and long distance track sectors. Neverthe-less, in this segment too there is a clear trend towards wheel detection and axle counting systems.

This white paper offers an overview of the specific features of public transport and the resulting challenges for track circuits and for wheel detection and axle counting systems. The advantages and disadvan-tages of the individual technologies are compared.

WHITE PAPER | EN

Frauscher Sensortechnik GmbH Gewerbestr. 1 | 4774 St. Marienkirchen | AUSTRIA T: +43 7711 2920-0 | F: +43 7711 2920-25 E: [email protected] | www.frauscher.com

Author:

Gerhard Grundnig Christian Pucher

Feb 2013

© Frauscher Sensortechnik GmbH | 2012 | EN

Track circuits versus wheel detection and axle counting in public transport systems



TABLE OF CONTENTS

About Frauscher

Frauscher Sensortechnik GmbH is the leading supplier of inductive sensor technology for use in the rail industry. The company was founded by Josef Frauscher in 1986 and employs more than 125 people. The export ratio of the company is 90%. Frauscher Sensortechnik’s portfolio includes the development, planning and production of innovative, highly-available and fail-safe sensor technology, as well as wheel-detection and axle-counting systems for a very wide range of technical rail applications. This also includes individual planning and pro-ject planning, as well as support during installation and commissioning.

1. History of public transport 4

2. Types of rail-based public transport 4

2.1 Light railways 4

2.2 Trams 5

2.3 High-speed trains 5

3. Legal framework conditions (EBO vs. BOStrab) 5

4. Particular requirements of SPNV 6

4.1 Vehicles, rolling stock 6

4.2 Rail beds and environment 8

5. Track circuits in public transport 9

6. Wheel detection and axle counting in public transport systems 10

7. Track circuits versus wheel detection and 11 axle counting in public transport systems



Practical experience from public transportation projects implemented worldwide has shown that the benefits of modern wheel detection and axle counting systems also considerably outweigh the negatives in this sector. Preconditions for this are, however, project-specific adaptations, which should be discussed and drawn up in advance, together with operators, system integrators and axle counting man-ufacturers. The reason for this is that due to the wide variety of vehicle types and structural conditions the framework conditions require customer-specific, often pro-ject-specific solutions.

In this segment the challenges to the manufacturers and wheel detection and axle counting systems are particularly demanding. Extensive expertise and services such as advice, laboratory tests or trials are required along with the capability to adapt hardware and software components to the respective project requirements.

New lines and projects are increasingly being equipped with modern axle counting systems due to the benefits in terms of functionality and operating costs. Nowa-days even in railed public transport systems, there is a clear move from track circuit systems to wheel detection and axle counting technology.

EXECUTIVE SUMMARY



Public transport has its historic roots in regular journey connections across rivers and lakes. In the second half of the 19th century, rail-based public transport (SPNV) saw a revival when, due to the industrial revolution , towns and industrial regions expand-ed significantly and the population increased. Those responsible for transport initially responded to this with the construction of the horse-drawn tram network, and 1890 saw the start of the triumphal procession of electric trams (trams, street cars, elec-trical), as well as of electrically operated underground systems . In millions of towns, the level of traffic increased so rapidly however, that by around 1900, trams had to deal with traffic congestion and unreliability. In order to improve the capacity of pub-lic transport, rail-based transportation systems were therefore given their own routes either above or below ground (elevated railways, underground railways, metro and suburban railways).

As the car became an increasingly popular mass transport method in the mid 1950s, the number of passengers travelling by railed public transport decreased. It was only within the scope of the environmental discussions which began at the start of the 1970s that attempts were made to win back lost ground through the formation of transport associations in accordance with the motto “Different transport companies; one ticket” and with an agreed timetabling structure that was independent of any company.

Rail-based commuter transportation systems are the most important pillar of public transport today.

The individual types of rail-based public transportation systems (SPNV) can be differ-entiated between and/or defined in the following way: [1

Light railways are, in some stretches, operated completely separately from road traffic as underground systems. In areas outside towns, they travel above ground on

1. History of public transport

2. Types of railed public transport

Figure 1: Trams rely on innovative axle counting technology

2.1 Light railways



2.2 Trams

2.3 High-speed trains

Trams are electrically operated railways that are either run on grooved rails set into roads (street-level rail beds) or on special rail beds.

Trams are subject to the local road traffic regulations when using the public transport.

Urban high-speed railways are predominantly self-contained electrically operated rail-way systems which serve public transport within a town (elevated railways and underground railways) or region (high-speed railways) and follow a rigid timetable with frequent trains throughout the day. High-speed railways have the absolute right of way on the few level crossings which are at the same level as road traffic.

The German Railway Building and Operating Regulations (EBO) is an ordinance that was introduced in Germany for the construction and operation of railways. The EBO is also in general use as a benchmark on an international level. The objective of the EBO is to standardise all rail systems and vehicles such that they fulfil safety require-ments. It regulates the methods of construction and operating of numerous rail facilities (e.g. platforms, level crossings, signals, points, etc.) and defines a number of terms for rail systems and operations.

Railways generally came into being to link towns, regions, countries and continents. High-speed passenger trains and heavy-goods freight trains generally travel on the same tracks. Railways always have a special rail bed and the spatial sequence of trains is controlled using signals. The EBO is used for this international railway network.

Figure 2: Modern tram systems rely on axle counting systems

special rail beds. Intersections with roads are at the same level and priorities are governed by standard road traffic signalling systems, rather than light railways having absolute right of way.

3. Legal requirements



The urban railway is the modern successor of the horse-drawn tram network, which developed into the tram network and ultimately into the railway over the next century. Train drivers usually drive based on what they see and are responsible for the route themselves. However, this does not apply in tunnels or on single-track distances.

High speed urban railways and underground railways have expanded historically but are still generally administered at a local level. The ordinance for the construction and operation of trams (BOStrab) is designed as a standard set of rules for all users.The significant differences between EBO and BOStrab are listed below:• Design parameters for track construction• Mandatory structure gauge • Level crossings• Speeds of travel• Vehicle guidelines• Braking capacities

In the context of public transportation systems, there are sometimes significantly dif-ferent requirements for wheel detection and axle counting systems as compared with standard-gauge railways. In the following we will try to outline the variety and com-plexity of these demands.

As mentioned at the start, BOStrab allows for considerably more design scope than EBO in the structural design of vehicles. This is a historical development but is also related to manufacturers/operators. Track vacancy detection systems must be completely compatible with these circumstances.

There are high and low wheel flanges, narrow and wide running surfaces and a wide range of wheel diameters. These wheel geometries and wheel flanges have a direct influence on reliable wheel detection. Small wheel diameters of up to 300 mm and small wheel flanges of up to 20 mm in height are not uncommon in this field. The range of dimensions in this regard is very varied and must be taken into account.

Wheel sensors have defined and clearly determinable spheres of influence and sensitivity areas. As a result of this, the sensitivity to approaching iron masses is differentiated accordingly. In the case of trams, metros, underground vehicles and urban transport trains, optimised truck geometries combined with electromagnetic brakes often result in problems with secure and available wheel detection.

The figures show a small cross-section of possible arrangements of electromagnet-ic brakes in trucks. The resulting characteristics of the analogue wheel sensor current are also depicted here.

4. Particular requirements of rail-based public transport

4.1 Vehicles, rolling stock

4.1.1 Wheel geometries and wheel flanges

4.1.2 Truck geometries and electromagnetic track brakes



The different influences of the electromagnetic brakes are clearly visible. What is more, different assembly heights and positions make safe and reliable differentiation of axles and electromagnetic brakes more difficult. [2]

Rail feedback currents create concentric magnetic fields around the track which lie within the range of influence of the wheel detection components. In the case of contact wire short circuits, rail feedback currents of 15 kA and higher may occur.

IGBT converters and low-loss service inverters require high switching frequencies and steep switching flanks. Therefore, with rail-based vehicles, disruptive magnet-ic fields are to be expected, which demonstrate a wide spectrum of technical energy frequencies.

Figure 3: Illustration of analogue sensor signals due to different truck geometries and electromagnetic brakes

4.1.3 Rail feedback currents

4.1.4 Magnetic fields



The rail beds and their environment in public transport vary in many respects from those of standard-gauge railways.

Alternating current tractions are sometimes used in public transport systems but direct current tractions are more prevalent. Power supplies range from 600 to 1500 V DC. The direct current tracks can be arranged as overhead rails, however these are usually arranged as so-called “third” rails in or alongside the track bed. Figure 4 shows an elevated railway application in Germany with direct current traction (750 V DC), which is run in a third rail alongside the track.

The wheels and the wheel flanges of trams often run on grooved rails. These grooved rails are surrounded by concrete or solid bedding material.

4.1.5 Maintenance vehicles

4.2.1 Traction

4.2.2 Track profiles

Figure 4: Wheel detection systems must be resistant to direct current trac-tions running parallel to the track, amongst other things

Figure 5: Robust and compact enclosure of the wheel detection components

In addition to regular vehicles, different maintenance vehicles such as trolleys for materials and tools, two-way vehicles or inspection vehicles also run on the tracks, usually outside operating hours. These are often highly idiosyncratic in terms of truck and wheel geometries.

4.2 Rail beds and environment



5. Track circuits in public transport

Track circuits work with a track section in which one or two rails are isolated from one another and from the ground. An electric voltage from 1 V to 3 V is applied to the iso-lated rail (and/or to isolated rails) (idle current principal). Unless the circuit is broken, the track vacant system registers a vacant state. If the circuit is broken e.g. short-cir-cuited to another rail by the axle of a railway vehicle or due to a technical fault, the track vacant system registers a busy state.

The use of track vacant circuits involves evaluation of the following points when planning the operating system, the vehicles and maintenance : [3]• Sensitive to disruptive currents from vehicles• Bedding resistance of track sections• Axle shunting circuits• Maintenance required for isolating joints• In addition to actual vacancy, logistical vacancy is also required at the interlocking

system level• Restrictive meshing of traction current feedback circuits in electrified railways• Track-mounted components must be insulated• Monitoring of long sections of track is costly• Lubricant or dirt between the wheels and rails may potentially limit availability

Along with project management requirements, the use of track circuits is highly in-vestment- and maintenance-intensive (insulating joints, connectors, meshing, track terminals).

A frequent argument for selecting track circuits is the detection of rail breaks. This context however is only applicable to a certain extent. Due to the meshing of the current feedback cables in rail lines (bridging), rail breaks cannot be detected by the track circuit in these areas. Rail breaks can only be detected on isolated sections of track [3]. Of the many investigations and studies that exist, the majority conclude that track circuits in no way guarantee reliable identification of rail breaks.

Waterlogging and flooding around the grooved rails and the self-contained design require special protective measures for wheel detection components on the track, their cabling and clamps.

In the area of public transportation systems in particular, wheel detection points may be driven over, trodden on or become dirty. This requires technical, operational and structural remedies.

4.2.3 Flooding and waterlogging

4.2.4 Driving over tracks and crossing by foot



6. Wheel detection and axle counting in public transport systems

Frauscher wheel sensors are mounted on the inside of the rail and detect the influ-ence of the wheel flange with upward-directing coils. The field lines of the transmis-sion coils, which for instance in the RSR180 wheel sensor are in the centre of the wheel sensor housing, flood the two sensor coils. When traversed, the induced voltages change as the field lines curve. This effect is used to detect the wheel flange and thus the axle.

The wheel sensors comprise two sensor systems with the two receptor coils ar-ranged in line along the rail. In this way, both detection of the vehicle direction and the safety level (CENELEC SIL 4) can be guaranteed. The two signal values on the wheel sensor are available as load-independent current values. These can be evaluated/an-alysed over the entire length of the cable by an intelligent evaluation board in the in-door equipment using different algorithms.

When using axle counting systems the following points must be observed: [3]• An operating directive must be produced for basic axle counting settings• Problems arise in permissive travel modes in conjunction with the axle counting

basic setting• If the setting is inaccurate, activated or low hanging track brakes are detected• May detect influences from converters in vehicles• Wheel dimensions• Rail wear-and-tear• Operating and display elements are required for axle counting sections (central/

decentral)

Once axle counting system are not affected by the bedding resistance of the tracks or the axle shunt circuit value of the vehicles, benefits emerge with respect to availa-bility. Further reasons in favour of axle counting systems are low investment as compared to track circuits and the possibility that axle counting systems can be in-stalled under the “rolling wheel” alongside track vacancy systems when upgrading/changing train safety systems without interference of the superstructure.



7. Track circuits versus wheel detection and axle counting in public transport systems

The table below compares the key features of these two technologies: [3]

Criterion Track circuitWheel detection and axle counting

Bedding resistanceMust be above 1.5 Ohm x km

Non-critical

Axle shunting circuit valueMust be less than 0.1 Ohm in track circuits

Non-critical

Rail break detectionMay not always be de-tected in track circuit systems

Rails breaks not detected in axle counting systems

Isolation jointsNecessary at least in points

Not necessary

Traction feedback current meshing

Requirements to be taken into account for meshing the traction feedback current

Not very relevant

Isolation intensityNon-isolating with railway thermal expansion joints

Intensive

Effective length (maximum length of a travel section)

Limited, depends on the superstructure, max. ap-prox. 700 metres

Unlimited

Logical vacancy signalling of interlocking system

Required Recommended

Reset Not required Required and critical

Procedure after power outage or commencing operation.

Section is physically va-cant but logically busy and is "freely travelled" by a pantograph test

Section is physically busy, the "free travel" process must be outlined in the operating directive

50-Hz monitoring on vehicle

Depends on construction type

Not required

Maintenance outlay High Low

CablingStar quad with four-core configuration

Start up after conversion

Problematic because start-up in parallel with track circuits in operation is difficult

Less problematic becau-se they can be fitted and started up in parallel with track circuits

Investment costsHigh (costs of isolation joints)

Better

Permission Available Available

Spare parts Many part types Fewer part types

Wheel profile N/A Applicable



Rail profile N/A Applicable

Rail wear-and-tear N/A Applicable

Influenced by converters in vehicles

No influence Influences rare

Electromagnetic track brakes

No influence Possible interference

Influence due to metal abrasion

Significant in the case of isolation joint

Significant in the case of wheel sensor

Track circuit technologies are currently the most widespread in public transportation systems. However, it is clear that the benefits of the axle counting systems outweigh those of track circuits in terms of life-cycle costs, safety and availability. Negative effects as a result of isolation shocks, isolation problems, dirt, leaves, salt, etc. are not an issue in axle counting technology. What is more, any track layouts (narrow and complex points, gridirons or level crossings) can be achieved.

The critical factors or possible disadvantages can now be overcome thanks to inno-vative and high quality wheel detection components. [4, 5]. Modern wheel sensors and intelligent analysis software also open up a range of added functions.

A more detailed white paper entitled “Modern wheel detection and axle counting in public transport systems” [6] describes the possible applications and specific solutions of Frauscher Sensortechnik GmbH.



BIBLIOGRAPHY

Contact

Frauscher Sensortechnik GmbHGewerbestraße 1 | 4774 St. Marienkirchen | AUSTRIAT: +43 7711 2920-0 | F: +43 7711 2920-25E: [email protected] | W: www.frauscher.com

The Authors:

Gerhard GrundnigSales, Head of Business [email protected]

Christian PucherHead of [email protected]

[1] Fiedler, J.: Bahnwesen, Werner Verlag, 5. Auflage 2005

[2] Frauscher J. / Thalbauer R.: Aufzeichnung und Analyse störender Ein wirkungen auf induktive Radsensoren, SIGNAL+DRAHT, 2008, Heft 7+8

[3] Verband deutscher Verkehrsunternehmen, Achszähleinrichtungen im ÖPNV, Mitteilung Nr. 3307, Dezember 2005

[4] Rosenberger, M.: Die Herausforderungen an Raddetektion und Achszählung in der Zukunft – Teil 1, SIGNAL+DRAHT, 2011, Heft 9

[5] Grundnig, G.: Die Herausforderungen an Raddetektion und Achszählung in der Zukunft – Teil 2, SIGNAL+DRAHT, 2011, Heft 12

[6] Grundnig, G. / Pucher C.: Moderne Raddetektion und Achszählung im Nah verkehr , Whitepaper 2012

media_Whitepaper_Gleisstromkreis - Track circuits versus wheel detection.pdf

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