Keywords

1 Introduction

The main railway subsystems have been involved in continuous evolutions that have allowed the development of increasingly fast, efficient and, above all, safe transport.

Making a special focus on the energy subsystem, the authors of this article have observed that, during the last decades there have been significant advances in the standardization of systems and components. These developments have evolved from what it can be considered guidelines to the application of authentic manuals of good practices, whose level of detail allows the development of the works in an unambiguous way, reducing the subjectivity and the possibility of interpretation of the normative documents.

It is worth asking at this point if the difference between a flexible catenary system and an overhead contact rail system is insurmountable, so that the requirements established for one cannot be directly applicable to the other. The evolution of flexible catenary systems has gone hand in hand with the increase in the maximum operating speed at which trains can circulate. The main aspect that has been modified is the complexity of the assembly of the overhead contact line, supporting cables, Y-Greek hangers, independent compensation systems for the different wires that make up the system have been added, which, for practical purposes, allows the search of a geometrically uniform system achieved by increasing the rigidity of the assembly to the detriment of its elasticity. The range of solutions currently available and widely used should be considered, since otherwise, there are gaps that condition the search for intermediate solutions that allow favoring the operating conditions, maintenance, and the quality of electric current transmission for railway traction.

2 Normative Framework

To establish a simple search and comparison criteria within standards, the word “rigid” and the acronym ROCL for Rigid Overhead Contact Line will be used as key terms as rigid upper contact line or rigid catenary.

EN 50,119:2020 is focused on the installation characteristics of railway current collection systems and recently updated, it can be observed that the word rigid is referenced within the document itself. 15 times, of which only four of them are specific for rigid catenary systems. The ROCL acronym is used only 4 times, linked precisely to the definitions and nuances provided about the catenary system in question.

Given that contact force limits are imposed for the rigid catenary system, it is immediate to introduce the standard EN 50,367:2020, which contains the criteria to achieve technical compatibility between pantographs and overhead contact lines. Then, it focuses on establishing certain parameters and conditions that allow guaranteeing a current transmission between the infrastructure and the rolling stock in a continuous and stable way possible.

Standard EN 50,317:2012 includes the requirements and validation of measurements of the dynamic interaction between pantograph and overhead contact lines, once again completely lacks references to the criteria considered. EN 50,318:2018 standard should therefore be considered, focused on the validation of the dynamic interaction between pantograph and catenary.

3 Simulation Tools Utility

There is a preliminary vision of the electrical and mechanical coupling of the components in particular conditions when simulation tools are used. Credibility finds the correspondence to the standards reference. The simulation process allows to study the quality of the current transmission and to evaluate the continuity of the contact, as well as its aggressiveness with the materials of the contact wire and of the pantograph plates.

For the electrical case, an increase in the contact force leads to an increase in the real contact area between the components of the pantograph and the catenary, so that the resistance to the current at that point is reduced and a minor temperature increase is produced. Reducing the contact force produces the reverse effect, reducing the area of current transmission, increasing the electrical resistance at the point of contact and increasing the temperature.

The extreme case would be for a loss of contact, with the consequent formation of electric arcs at the instants in which both components are very close, but not in contact. The formation of an electric arc is the worst possible situation, since the temperature increase is so high that it can cause loss of material due to its melting. All this, and its application to component wear calculations, is collected according to Archand's formulation (Fig. 1).

Fig. 1.
figure 1

Wear depth profile of a pantograph plate. Source. Own elaboration

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4 Model Development for OCR

This process has been carried out within the framework of the development of the UIC International Railway Solution (IRS) 70,020, which aims to establish a series of recommendations that can guide to the inclusion of rigid catenary systems.

The generated model is based on the use of finite elements [1,2,3] for the resolution of the rigid catenary structure. Because the main beam of the assembly consist on an element of constant section, the inclusion of the physical characteristics is especially simple within the matrix structure used to solve the problem (Fig. 2).

Fig. 2.
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Simplification of the rigid catenary system through finite elements. Source. Own elaboration

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For each element considered, twelve degrees of freedom are taken into account, since, as it is a highly rigid system, the small torsional displacements that occur during the assembly conditions the local behavior of the system.

The simplification of the catenary supports is also considered as an element that only allows vertical displacements of the catenary at the mooring point, so that a node of the beam can be made to match the extreme node of the support and thus close the configuration of the catenary [1, 4, 5]. In the case of the pantograph, the standards themselves include simplified mass models. The use of this type of multibody models has been shown over time to faithfully reproduce the dynamic requirements that are demanded of it, which is why they have been incorporated into the standards. In addition, pantograph manufacturers provide values for this type of reduction with each model they sell.

The integration of both models can be done in a matrix, establishing a relationship of position and mutual force at the point where contact occurs. This point moves in time, so an integration method is needed that can allow the calculation of the temporal evolution of each point or node that composes the structure of the system. With time evolution, we want to refer to the fact that for each point of the system, it is necessary to know, mainly, its position, displacement speed and acceleration, as main variables. In this way, the behavior of the catenary system can be known before the passage of the pantograph, at the exact moment and the behavior of remaining energy dissipation, which sometimes conditions the quality of capture of a second pantograph of the same composition.

For this task, the HHT algorithm (Hilber, Hughes and Taylor) has been used, which is widely applied in the calculations of structural dynamics. One of the main advantages of this method is that the numerical damping can be controlled and adjusted according to the test conditions to adapt it to the reality of the structure. In addition, it allows improving the convergence of the problem, being a robust method of obtaining results in linear and non-linear systems. [6,7,8,9]

5 Model Validation

In this work, comparison methods to existing standards for flexible catenary and lab and on-fied tests has been used to validate a simulation for the rigid catenary. The first validation step has been carried out applying the methodology for defining the model and calculating solutions on flexible catenary systems in accordance with the provisions of the EN 50,318 standard. If a spatial position relationship is established to this together with the link with the elements of the environment, the construction of structures is independent of the electrification system.

There is only one exception, and that is the calculation of the length of the hangers. From the installation, they require a variable strength depending on the length of the spans. To address this problem, previous system adaptation periods have been used to calculate the length of the hangers to ensure that the contact wire meets technical and regulatory requirements. Once the simulation method has been tested and its validity verified with respect to the standards, we proceed to the construction of a standard rigid catenary system, considering spans of 10 m distance. Firstly, a series of model characterization tests are carried out for comparison with the real installation to which access is available. These tests are focused on the study of static deformations and the identification of the main natural modes of vibration of the system. For all the tests, a great similarity can be seen with the results obtained, which allows us to assume that the model responds adequately to the previously established verifications (Fig. 3).

Fig. 3.
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Detection of the main modes of vibration of the rigid catenary system. Source. Own elaboration

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It remains, finally, to evaluate through comparison the dynamic behavior of the set and its ability to emulate the response of the system under operating conditions. To do this, a test scenario identical to the one provided by SBB is programmed in the tool so that, through direct comparison of the statistical values related to the contact force, as stated in the applicable standards, the correctness of the results can be evaluated with the application of the calculation methodology. For the specific case of an installation with spans of ten meters in length, a static force of 85 N and a circulation speed of 110 km/h, we have the following comparative Table 1.

Table 1. Validation of the simulation tool through comparison with real measurements. Source. Own elaboration
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The EN 50,318:2018 standard admits a deviation of the mean force values of ±2,5 N and 20% for the standard deviation value. It can be verified that all the results are framed within the requirements, although the comparison of the elevation of the supports and the displacement of the pantograph head cannot be made since there are no data available, but a result is expected within the required limits given the quality of the result obtained with respect to the forces.

6 Conclusions

It can be concluded that the use of virtual simulation tools is possible and recommended on electrification systems based on rigid catenary for helping the analysis in the life cycle before and during operation. In particular the work has been achieved to define and to analyze fundamental aspects during IRS 70,020 development.

Even though Rigid Contact Line is a widely extended system and whose use is mainly based on suburban transport systems but the use of this solution in main lines and high speed lines when infrastructure is major favorable for its application (tunnels in main track or urban tunnels), the current standardization standards continue to consider this system as something residual, meaning that the results of the simulations can be framed in ranges of validity.