FEM of strain and thermal load of a train current collector with contact force during interaction with catenary

N. Theune1, T. Bosselmann1, R. Röckelein1, K. Schleicher1, W. Ecke2 & K. Schröder2 1Siemens AG, Corporate Technology, Germany 2IPHT Jena, Optics Division, Germany

Abstract

This paper reports on FEM modelling results simulating the effect of current on the collector strips thermal and strain characteristics during the interaction between pantograph and overhead contact line. Keywords: Fiber Bragg Grating, temperature and strain monitoring, overhead contact line, catenary, pantograph, contact force, collector strip, panhead.

1 Introduction

All railway companies aim for higher reliability and availability in train operation. As a consequence the quality of train control systems as well as monitoring equipment for the next generation of high speed railway lines needs to be improved. The deregulated rail market forces condition monitoring of infrastructure and rolling stock. This goal can only be achieved if the interface of rolling stock and infrastructure, i.e. current collector and overhead contact line (OCL) is monitored accurately with respect to contact force, thermal load and dynamic strain to avoid excessive wear [1]. Up to now diagnostic systems for the online measurement and control of the thermal and dynamic strain load and wear of the carbon strips of train pantographs are not available. Little is known about the amount of strain and thermal load in the carbon strip during operation. The goal of the European SMITS project is the measurement of these parameters as well as a theoretical investigation by simulation to achieve fundamental information about the collector strip and the overhead contact wire interaction.

Computers in Railways IX, J. Allan, C. A. Brebbia, R. J. Hill, G. Sciutto & S. Sone (Editors)© 2004 WIT Press, www.witpress.com, ISBN 1-85312-715-9

This information could consequently be applied for diagnosis of data for a condition dependent maintenance and replacement of carbon strips. Furthermore not only the wear condition of a collector strip, but also the precise magnitude of contact force could be drawn out of this data. Another goal for the future is to provide reliable steering information towards an actively controlled pantograph [5]. A fundamental Finite Element Model has been composed and the thermal and strain interaction between the collector strip and the overhead contact wire has been simulated under various ambient conditions. Furthermore the modal analysis of contact strips reveals resonances that can possibly cause arcing and short current breakage during train operation. The theoretical results have been correlated with experimental data. To measure temperature distribution, strain load and modal resonance data at electrical voltages of up to 25kV, the required sensors needed to be easily integrable in the catenary construction and must be able to measure on high voltages of up to 25 kV. In general conventional electrical sensor techniques could be applied, but due to the high voltage level on top of the pantograph an enormous amount of effort needs to be put into the insulation of these sensors or into provision of independent power supplies etc. [2]. On the other hand fiber-optical sensors offer, because of their vitreous nature, a simple way to measure on high voltages with a minimum of insulation material needed. Fiber optical sensors on the basis of Fiber Bragg Gratings (FBGs) have been integrated in carbon strips and investigated in a laboratory setup. As an outcome for the first time a fundamental understanding of the thermal and strain processes in the carbon strip is possible. The experimental data are used to provide reliable reference points for an improved computer model. Finally this is then used to calibrate sensors for contact force and wear monitoring.

2 Brief theory of Fiber Bragg Gratings

As in [3] a change in fiber strain ε∆ and temperature T∆ is connected to a change in center wavelength λ∆ of the Bragg reflex via the two equations

ελλ

∆⋅−=∆ )1( ep ,

Tpe ∆⋅+⋅−=∆ ])1[( ξαλλ ,

(1)

whereas ep represents the photoelastic constant, α the linear coefficient of expansion and ξ the thermooptical coefficient of the fiber. Almost in any case where FBGs are part of a composite material both effects, temperature and strain, contribute to a center wavelength shift of the Bragg reflex. In order to measure both – temperature and strain – independently the usage of self-contained sensor housings is necessary. This was done through a sensor design that decoupled any stress acting on the sensor housing, e.g. elongation of carbon through ohmic heating or arcs.

Computers in Railways IX, J. Allan, C. A. Brebbia, R. J. Hill, G. Sciutto & S. Sone (Editors)© 2004 WIT Press, www.witpress.com, ISBN 1-85312-715-9

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3 Modelling of current collector – contact wire interaction

The objective of the European SMITS project is an optical strain gauge monitoring system which is deployed on the current collector of a fast train pantograph to measure temperature and force between OCL and collector [4].

Figure 1: FEM Modelling of the carbon strip of a European panhead to determine force induced strain.

From that information the normal and excess wear of OCL and collector shall be evaluated. Moreover data about user caused wear, life time, life cycle cost, and predictive maintenance of OCL as well as train shall be derived. A Pan European design carbon strip according to the TSI Energy was modelled, well suited to be mounted on top of a European panhead as in Figure 1:. The 3D simulations, as in Figure 2: (strain load) and Figure 3: (thermal load) was carried through with the following simplifications: (a) bonding interface neglected and (b) symmetrical load and boundary conditions. The modal analysis reveals relevant resonance frequencies that range from 7Hz up to 1200Hz, whereas resonances beneath the sampling rate of 500Hz need strongly be avoided. In Figure 2: the strain distribution inside the current collector with respect to 3 different sensor heights inside the carbon – aluminium support is shown. The strain along the profile axis is strongly dependent on the z-position of the strain layer and exhibits an approx. linear behavior between the ends of the carbon strip.

Computers in Railways IX, J. Allan, C. A. Brebbia, R. J. Hill, G. Sciutto & S. Sone (Editors)© 2004 WIT Press, www.witpress.com, ISBN 1-85312-715-9

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Figure 2: Strain under load force.

Figure 3: Electro thermal analysis of Euro panhead, temperatures in °C.

Computers in Railways IX, J. Allan, C. A. Brebbia, R. J. Hill, G. Sciutto & S. Sone (Editors)© 2004 WIT Press, www.witpress.com, ISBN 1-85312-715-9

872 Computers in Railways IX

Carbon strip B5: 100N asym.

0.00E+00

1.00E-05

2.00E-05

3.00E-05

4.00E-05

5.00E-05

6.00E-05

7.00E-05

8.00E-05

9.00E-05

-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5

Profile axis [m]

Stra

in

1.18E-022.76E-024.33E-025.91E-027.48E-029.06E-021.06E-011.22E-011.38E-011.54E-011.69E-011.85E-012.01E-012.17E-012.32E-012.48E-012.62E-012.76E-012.89E-013.02E-013.14E-013.25E-013.36E-013.46E-013.56E-013.65E-013.74E-013.82E-013.90E-013.98E-014.05E-014.12E-01

Figure 4: Modelling of contact force induced strain and position resolved.

To get a good estimation about the thermal heating of the current collector strip during operation a steady state electro thermal analysis was carried through, as in Figure 3:. The thermal convection was assumed to depend linearly on speed. The contact resistances between contact wire and carbon strip was measured in a laboratory setup and ranged between 16mΩ and 24mΩ for typical contact forces of about 70N. Thermal radiation was included while the ambient air temperature was assumed to be fixed at 25°C. In Figure 3: the electro thermal analysis of a Euro panhead current collector was performed. The Zig-Zag of the contact wire was also incorporated into the model. This results in a smearing distribution of the thermally heated strip surface. The data of the simulation have been cross checked with experimental data. So far simulated and experimental data agree quite well, experimental tests and simulations will be continued.

4 Conclusions

The modelling and first field tests have demonstrated the possibility to acquire information about the interaction between OCL and current collector via optical strain gauges integrated into conventional current collector strips.

Acknowledgements

The authors thank the partners of the SMITS consortium for support, especially Matthias Jenzer and Martin Kocher from BLS Bern-Lötschbergbahn AG. Part of this work was financially supported by the European SMITS project.

Computers in Railways IX, J. Allan, C. A. Brebbia, R. J. Hill, G. Sciutto & S. Sone (Editors)© 2004 WIT Press, www.witpress.com, ISBN 1-85312-715-9

Computers in Railways IX 873

References

[1] Kohlhaas, J.; Ortstädt, W.; Puschmann, R.; Schmidt, H.: ”Interoperable overhead contact line SICATH1.0 for high-speed line Cologne-Rhine/Main”. Elektrische Bahnen 100 (2002), H. 7, S. 249-257.

[2] Kießling, F.; Puschmann, R.; Schmieder, A.; Schmidt, P.: “Contact Lines for Electric Railways – Planning, Design, Implementation”. Siemens AG, Publicis Corporate Publishing, Munich, 2001.

[3] Theune, N.M.; Bosselmann, T.; Kaiser, J.; Willsch, M.; Hertsch, H.; Puschmann, R.: “Online Temperature Monitoring of Overhead Contact Line at New German High-Speed Rail Line Cologne-Rhine/Main”. Conference Proceedings, CompRail 2004, 17.-19. May 2004, Dresden, Germany.

[4] Poetsch, G.; Baldauf, W.: ”Simulating the interaction between pantographs and overhead contact lines”. Elektrische Bahnen 99 (2001), H. 9, S. 386-392.

[5] Baldauf, W.; Behr, W.; Heine, Ch.; Kolbe, M.; Blaschko, R.; Richter, H.: ”Actively controlled acoustically optimised single arm pantograph ”. Elektrische Bahnen 100 (2002), H. 5, S. 182-188.

Computers in Railways IX, J. Allan, C. A. Brebbia, R. J. Hill, G. Sciutto & S. Sone (Editors)© 2004 WIT Press, www.witpress.com, ISBN 1-85312-715-9

874 Computers in Railways IX