Automatic Systems for Wear Measurement of Contact Wire in Railways

S. Borromeo, J.L. Aparicio Universidad Polittcnica de Madrid

E.T.S.I. Industriales. Divisi6n de Ingenieria Electr6nica C/ Jose GutiCrrez Ahascal, 2.28006 Madrid. Spain

Tel. +34 91 3363191; Fax. +34 91 5645966 e-mail: Jsusana; apa)@upmdie.upm.es

Abstract - Measuring systems that detect automatically the degree of wearing of the contact wire in railways are necessary in order to carry out an efftcient infrastructure management and maintenance based on contact wire condition. This paper describes automatic methods to measure the wear of overhead wires, in particular, those based on optical detection techniques. Different automatic systems that measure the wear will be outlined. The measuring basis of dillerent approaches, type of illumination and optics used, acquire and processing procedures will be studied. A comparative analysis of technical solutions adopted by each of them will be shown and the major advantages and disadvantages are highlighted.

1. INTRODUCTION

Catenary maintenance is a significant part of the total maintenance investment in railways. Overhead line conditions are very important for power collection performance and due to this reason an effective maintenance of catenary is required for an efficient operation.

The continuous friction between the pantograph and the wire produces a wear that reduces the effective cross section of the wire. Contact wire wear measurements are necessary in order to ensure railway service quality and security. Furthermore, they allow to detect at early stage any deterioration of contact line which results in an excessive wear and correct it, especially important for new lines at the beginning of system lifetime. Contact wire lifetime can be extended controlling the residual wire thickness.

Fig. I . Overhead wire The traditional method of maintenance of the overhead

wires is performed manually, by personnel operating from the platform of the ladder coaches, previous unpowering and earthing the overhead contact lines, during breaks of circulation. Rail network inspection is not completely executed, the section that is going to he inspected is selected

based on historical data. Automatic systems for wear measurement of contact wire are necessary to avoid the disadvantages of manual inspection.

Nowadays there are three automatic systems in use: MEDES system developed by UPM-DIE (Divisi6n de Ingenieria Electronica, Escuela Ttcnica Superior de Ingenieros Industriales, Universidad PolitCcnica de Madrid) and funded by RENFE (Spanish Railway

ATON (Automatic Thickness measurement of Overhead wires Netherlands railways) designed by TNO Institute of Applied Physics [4] Japanese system developed by Railway Technical Institute [ 5 ] .

In the next section the problem of automatic inspection will be outlined. Methods to measure contact wire wear, in particular optical detection ones, will he explained in Section 3. The operative systems already mentioned (MEDES, ATON and Japanese system) and other development [6], [7] under execution, that have been presented in Cologne in WCRROI(World Congress on Railway Research) will he described in the section 4. A comparative analysis of these systems is outlined in section 5 . At the end some conclusions are shown.

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11. DEFlNlTION OF THE PROBLEM

There has been a large increase in railway electric traction exploitation in the last 20 years. Maintenance operations involve interference with the train traffic. A preventive maintenance is necessary to get an efficient management of the service. As explained in former section the traditional method overhead wires maintenance is performed manually and has many disadvantages, in order to avoid them, an automatic inspection is necessary.

Different contactless measurement techniques have investigated [SI, namely magnetic fields analysis, microwave reflection analysis, electrical and optical detection systems. However, optical detection systems are those which have been successful. In the next section these systems will he explained in detail.

It is important to underline that all operative systems and the majority of systems under development are based on optical methods.

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Nowadays, there is only one approach that is not based on optical methods. It is under development by SCLE for SNCF (French Railway Company) [9]. Its measurement basis is based on a radar antenna, located in pantograph that emits at 25 GHz. The thickness is calculated by Fourier Transform of contact wire image.

All developments are conditioned by the following factors: Number of wires in measurement range. In the overlap section, there are four contact wires, so systems have to be able to measure them simultaneously. Measures have to he carried out at speed train. Systems have to acquire, process and store a considerable amount of data in real time. Contact wire height. Due to tunnels, road crossing, stations, the contact wire height varies.

*Contact wire stagger. The stagger is the horizontal displacement of the catenary and contact wires either side of the track centre line. The purpose of the staggering of the contact wire is to maximise the surface contact with the overall width of the pantograph. This reduces localised wear and increases the interval between pantograph replacements. Weather conditions: daylight, solar radiation, rains. Systems have to run at day and night.

111. METHODS TO MEASURE CONTACT WIRE WEAK

A . Contact Wire Catenary is the term given to the overhead line equipment

on an electric railway with the exception of the supporting structures. Although this term is widely accepted as referring to all the wiring, including the contact wire, strictly speaking it refers only to the catenary wire.

Fig. 2 Diagram of Overhead Current Supply System showing principal parts

The catenary wire is a cable that is supported at each overhead electrification structure and from which are suspended the droppers and contact wire. Masts and overhead structures are located at intervals along the railway. These are known as masts, portal frames, cantilevers or headspans. From these, the catenary wire is suspended. The droppers are hung from this wire. The contact wire is

attached to the ends of the droppers. The contact wire is the conductor from which the traction power is collected.

The contact wire is typically circular in cross-section and has two grooves formed longitudinally, slightly above the horizontal centerline, and equi-distant about the vertical centerline. This facilitates the attachment of the dropper connections and the registration connections at the cantilevers.

The contact wire can he manufactured from many different alloys of copper (cadmium copper, silver copper, etc.), and in hard drawn copper.

Railway companies use the residual thickness or cross section of the wire (RENFE) as indicator of the degree of wire wear.

Fig. 3 shows the section of new contact wire (left side) and the section of a contact wire with wear (right side).

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a = arcsit( T) Based on (1) and (2) the thickness (h) can be calculated

starting from the width of the wearing track (w):

h = r . 1 +cos arcsin - [ ( ;*.I1 (3) Applying that worn section is the area of the segment of

circle with central angle 2a the relationship between the worn section (A) and the width (w) of the wearing track can be described by:

B. Optical detection systems As explained before, different contactless measurement

techniques have investigated [SI. However, optical detection systems are the only successful ones.

The three main work lines have been the following:

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The width of the wearing track is illuminated and CCD cameras capture the reflected light. RENFE [I] , [2], [3], NS (National Railway Company of Netherlands)[4], IPM (Fraunhofer Institute of Physical Measurement Techniques IPM) [6], and FS (Italian Railway) [7] have studied this approach. Japan Railway approach has been the following: the width of the wearing track is measured by reflection return time [SI SNCF (French Railway Company) [9] bases its development on measuring the thickness by infrared photoelectric device.

The advantages of measuring the width of the sliding surface are the possibility to measure double wire systems, the measurements are done independently of overhead line equipment such as support points, hanger, dropper, and it is possible to obtain additional information on wearing track condition.

The major advantage of measuring the thickness is the low cost and the simplicity. However, it does not allow measuring two wires simultaneously. Another drawback is the necessity of modifying the pantograph.

IV. DESCRIPTION OF SYSTEMS

A description of operative systems already mentioned (MEDES system, ATON system and Japanese system) and the systems under development will be outlined.

MEDES system is installed and operative in laboratoly coaches used by RENFE and SNCF (under test). The system is in operation and the Spanish track network has been evaluated several times. Manual confirmations have shown the good behaviour of the measuring system.

Measuring coach of the Dutch Railways is equipped with a wire measuring system (ATON) and Japanese system is used to inspect Japanese lines.

A. MEDES and ATON Svstems MEDES and ATON systems have the same measurement

basis: the wearing track is illuminated with infrared light and the reflected image is captured with linear CCD cameras.

Both systems use laser diodes as illumination source with wavelength around 810 nm. A band-pass filter suppresses the backmound lieht from the skv.

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Fig. 4 Measurement basis of MEDES and ATON systems

Both systems include five overlapped CCD cameras to cover the stagger.

There are two possible solutions to achieve the necessary definition: telescopic or conventional optics. The first solution is used by ATON system. The main advantage of this solution is that the optical resolution is constant. However the cost, size and simplicity are penalised. MEDES system uses conventional optics simpler and easier than telescopic optics. The overhead wire is not always at the same height. Both systems use focus system to position the cameras with respect to the lenses.

The processing is complex, due to the large amount of data that must be processed in real time. So, MEDES system is capable of taking and processing 250 images per second independently on train speed. Each CCD camera has 2.592 pixels, so the system has to process 3,2 Mbyteds. Both systems carry out parallel processing by DSPs (ATON) or transputers [IO] (MEDES) to get that processing Capability.

UPM-DIE is developing a new processing system to improve MEDES performance. Targets of new development are: the increase in the number of measures per second (minimum 1000 per second), the compatibility with existing system (RENFE and SNCF) and the capability to elaborate reports on line. New system is based on programmable logic and is modelled in VHSIC Hardware Description Language (VHDL) and implemented in Field Programmable Gate Array (FPGAs) [ I l l . The advantages of these devices compared to DSPs, are concurrency (simultaneous execution of all control procedures) and technology independence.

Both systems are installed inside measuring cars. No component is mounted on the roof or installed on the pantograph, so, mechanical and maintenance problems are avoided.

B. Japanese system Measurement basis is the following: a laser beam scans the

whole stagger zone with a rotary mirror. When the laser beam catches the sliding surface of the contact wire, it causes irregular reflection and part of it returns to the light source, which is caught by a photoelectric transfer element and is used to measure the duration of reflection. Since the laser beam scans at a constant speed, the duration of the received refle on is proportional to. the width of the wearing track

Mirror I

Fig. 5 Japanese measuring system

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A diode pumped YAG laser (wavelength 1064 nm, output 350 mW) is used as laser light source.

The optical system consists of several mirrors and lenses. It is installed on the roof and its large dimensions are 2500 x 1000 x 400 nm. It is illustrated in Fig.5

This system also incorporates a servomechanism that moves one of the lenses with the change of contact wire height.

C. Systemfor contact wire rhickness measurement Measurement basis is shown in Fin.6.

Fig. 6 Contact wicc thickness measurement

This system does not allow measuring two contact wires simultaneously. To solve this problem, Cyhemetix (France) [9] is developing a system that will be able to measure two wires simultaneously. This system incorporates a device that elevates one of the wires, so, the maximum train speed is 5 K d h . This system has a horizontal limitation of Cl50 mm, therefore it does not cover whole horizontal displacement of contact wire (3500 mm for Spanish track and M50 mm for French one).

D. Systems under development

Measurement Techniques IPM I ) Development of Fraunhofer Institute of Physical

Fraunhofer IPM is developing optical inspection systems to monitor the overhead wires. Among them, there is a wire wear measuring system (WWS 101).

WWS 101 is installed on coach roof and it is equipped with two cameras with motorised zoom objective that capture frames from the illuminated sliding surface. Each frame corresponds to 25 mm wire length. It uses a row of white spotlight as illumination source. The viewing beams of both cameras are directed towards the contact wire by a mirror.

For its operation WWS 101 needs the contact wire position measuring system CRS204, developed by Fraunhofer IPM, to control the scan angle of plane mirror as well as the zoom cameras.

Images are transferred via optical fibres to the control computer where a software processing is camed out. Image processing algorithms and edge enchancing filters are applied to define the edges of the wearing track. The direction of the edges is calculated and averaged every 25 mm. Furthermore the width of sliding surface is determinate. This calculation procedure has an important problem: if there is a sharply slope change, such as in the mast, calculation errors will appear.

This system is not in operation yet. It is under test in Italy. 2) In WCRR'OI [7] was presented an integrated

diagnostic prototype (Geocat) installed in a special coach of FS (Italy). Geocat will check geometrical, mechanical and electrical parameters of contact lines. The width of wearing track is one of these parameters. The system designed to measure it will be installed on the pantograph. Vibrations on the pantograph can make mistakes. This system does not use laser illumination. It has only been tested in laboratoly and it does not check in line yet.

Table I lists the technical solutions adopted by each of system described.

Thc width o f the The wearing track is Lam diodes A= 8Un OIrrlapped Cameras Sophirtuatcd. w a h g ,rack illuminated with nm ~ o w l c x and

inhared llghl and wscomissd optics rcflretcd imgr 13 raptured w t h lincai CCD camms

I nsidcmrarunngcar 1 hogration I

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V. COMPARATIVE ANALYSIS

Solutions for automatic measuring system have been described in the former sections. The purpose of this section is to compare them.

As for the magnitude measured, there are two possible parameters to be measured: width of wearing track or contact wire thickneis. The advantages of measuring the width of the sliding/ surface are the possibility to measure double wire ystems, the measurements are done independently of overhead line equipment such as support points, hanger, dropper, and it is possible to obtain additional information on wearing track condition. The main advantage of measuring thickness is its low cost and its simplicity. However, its drawbacks are more important: limited measurement range, limited measurement speed and the maximum number of detectable wires is only one. Another disadvantage is the necessity of modifying the pantograph. All systems described in this paper measure the width of wearing track but the system described in section 1V.C. The wearing track should be several times brighter than the rest of image (the sky and other parts of the overhead wire) to simplify the processing of image. The best solution is to use a monochromatic source of light. Flash lamp or sodium light could be used, but their complexity, cost and mechanical and power considerations do these solutions unfeasible. A better solution is to use laser light and among laser solutions, diode laser is the best solution. Its benefits, compared with other laser sources as gas laser, are: small size, light, easy to cool, higher reliability and a very short time to be stabilised. On the other hand, the solar spectrum component is smaller at infrared wavelengths (see Fig.7), so the radiant energy to reduce the solar light is lower than at wavelength in visible spectrum. Besides, it is possible to reduce almost completely the effect of the skylight employing interferometric filter. Power emission is an important issue to consider when laser light is used. System must comply with Standard of Safety of Laser Product (EN 60825-1, for Europe). The three systems in operation use laser illumination, laser diodes (MEDES and ATON) or diode pumped YAG laser (Japanese system). There are several alternatives to cover the contact wire stagger. MEDES and ATON systems include five overlapped cameras. Japanese system employs a rotary mirror and the development of Fraunhofer IPM uses two cameras and their viewing beams are directed towards the contact wire by a mirror. Although the first solution includes a major number of components, it is best option because the other solutions complicate the optics system and they need additional systems that follow the contact wire.

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Fig. I Solar Radiation There are two possible solutions to achieve the necessary definition: telescopic or conventional optics. The constant optical resolution is the main advantage of telescopic optics. However, it is more expensive and complex than conventional optics. The overhead wire is not always at the same height, a focus system is necessary to position cameras with respect to the lenses. Another important factor in the design of measuring system is its location. It is desirable that no component of systems is mounted on the roof of measuring car to avoid mechanical and maintenance problems. It is not suitable to install systems on the pantograph structme because dynamic behaviour of pantograph is complex and measurements will be done under high voltage. Some systems that have modified the pantograph have important speed limitations and in other cases vibrations and interferences caused by high voltage could makes measurement errors. MEDES and ATON systems are installed inside measuring cars. The rest of systems described in this paper are mounted on the roof.

Having the technical solutions adopted by the different systems described in former sections as reference, it could say that MEDES system is the best approach. This system, developed by UPM-DIE and funded by RENFE is not only in operation in Spain. Other Railway Companies have been interested in it, among them, SNCF (French Railway Company). Its interest led up to develop a new MEDES device that is installed in SNCF laboratoly coach (Voitiere 1.E.E 142.9).

Fig. 8 Lab Coach IO02 (RENFE) Fig. 9 Coach 1.E.E 142.9 (SNCF) It is important to underline that SNCF [I21 and Japan Railway Company, were the first companies that proposed

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methods to measure the contact wire wear, although the French system has never been operative.

RENFE has registered the system with Spanish patent #9401633 and the European one #96500022.7 has been requested.

Although MEDES and ATON system have the same measuring basis and they have used similar technical solutions (laser diodes as illumination source, CCD overlapped cameras, parallel processing) MEDES has several advantages. The main difference between both systems is that ATON uses a sophisticated complex and customised designed telescopic optics, while MEDES system is based on electronic solutions and commercial optics. This fact makes the MEDES system easier and cheaper to maintain and operate.

Measurement basis of Japanese system is simpler than MEDES and ATON. Acquire and processing procedures are less complicated. However, its optic system is more complicated and larger and it has to use by qualified personnel. On the other hand, because the system is on the roof there are more mounted and maintained problems.

VI. CONCLUSIONS

In this paper we have presented a review of the most interesting solutions for automatic measuring of the wearing of overhead wire in railways, in particular those based on optical detection techniques.

The different alternatives adopted by the three systems in operation (MEDES, ATON and Japanese system) and the other systems under development have been compared highlighting their advantages and disadvantages.

Some studied issues are the measuring basis of different approaches, type of illumination and optics used, acquire and processing procedures. After a comparative analysis it could be said that MEDES system is the best development. This system is installed and

operative in laboratory coaches used by RENFE and SNCF (under test). This system is based on electronic solutions and commercial optics. Its good behaviour and reliability have been confirmed by manual check and several thousand of kilometres of Spanish track have been inspected.

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VII. REFERENCES

[ I ] S.Borromeo, J.L.Apancio, P.M.Maninez, MEDES: Automatic system for wear measurement of overhead wires WCRROI, November 2001.

[2] J.L.Apacio, E.De la Torre, Y.Torroja, P.L.Castedo, P.M. Martinez, Sensor for Railways Maintenance II School on Sensor, September 1995.

[3] Y.Torroja, Garcia.S, Aparici0,J.L. and Martine2,P.M. An artificial vision system used for measurement of the overhead I wire in railway applications IEEE Industrid Electronics , Conference (IECON), November 1993

[4] J.M.Van Gigch, C.Smorenburg, A.W.Benschop, Le systeme : de mesure de Iepaisseur des fils de contact des Chemins de fer neerlandais (NS). Rail International, AVrI 1991, pp 20-31

[SI TShimada, T.Kohida, Y.Satoh,Y. Development of Solid : Laser Measuring Apparatus of Contact Wire Wear,QR of RTN, Vo1.38,No.I,March 1997 pp 19-24.

[6] H.Hoefler, M.Seib, M.Dambacher,V.Jetter, High Speed Overhead Wire Monitoring, WCRRDI, November 2001.

[7] A.Fumi, A.Forgione,A new complete system for catenarys , checking. WCRROI, November 2001

[8] R.Miiller, Contact wire wear measurement devices. A system comparation WCRR97, November 1997.

[9] Forum Maintenance catdnaire. September 2000, Paris [IO] INMOS, 77ze Transpuler Dolobook. lnmos Limited, 1989 [ I I] T.Riesgo, Y.Torroja, E.De la Torre, Design methodologies

based on hardware description languages, IEEE Transactions on I~dustrinlEIectronics, vol. 46, no. I , pp. 3-12, Feb.1999.

[ 121 H.Mathieu, J.M,Dadonneau, and G.Rouan, Automatissation de la mesure de Iepaisseur du fil de contact des catenaires Reveu Gmkale des Chemis de Fer , May 1977, pp, 284-288

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