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Special issueElisabeth Helwig, Arnd Stephan, Dresden; Frank Pupke, Cologne

Life cycle costs of contact wires – Basics and first results

Special issueElisabeth Helwig, Arnd Stephan, Dresden; Frank Pupke, Cologne

Life cycle costs of contact wires – Basics and first results

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Overhead Contact Lines

Special issue

Life cycle costs of contact wires – Basics and first resultsElisabeth Helwig, Arnd Stephan, Dresden; Frank Pupke, Cologne

The contact wire type VALTHERMO® developed by nkt cables GmbH & Co. KG was investigated in a first field test in a commercially traversed line in comparison with conventional contact wires. The de-veloper and the Chair for Electrical Railways at Dresden University of Technology studied commonly the life cycle costs of contact line systems equipped with the new contact wire and with conventional ones. As a result of the study of various alternatives it was demonstrated that the new contact wire VALTHERMO yields considerable economic advantages for the operators of contact line networks.

LEBENSZYKLUSKOSTEN VON FAHRDRÄHTEN – GRUNDLAGEN UND ERSTE ERGEBNISSEDer von der nkt cables GmbH & Co. KG entwickelte Fahrdraht VALTHERMO® wurde in einem ersten Feldversuch im Vergleich mit herkömmlichen Fahrdrähten betrieblich erprobt. Der Entwickler und die Professur für Elektrische Bahnen der Technischen Universität Dresden untersuchten gemeinsam die Lebenszykluskosten von Fahrleitungsanlagen mit diesem neuen Fahrdraht. Im Ergebnis der Va-riantenberechnungen zeigte sich, dass der neue Fahrdraht VALTHERMO erhebliche wirtschaftliche Vorteile für die Anlagenbetreiber ergeben kann.

LES COÛTS DU CYCLE DE VIE DE FILS DE CONTACT – BASES ET PREMIERS RÉSULTATSLe fil de contact du type VALTHERMO® développé par nkt cables GmbH & Co. KG a été soumis à une première épreuve sur le terrain en le comparant aux fils de contact conventionnels. Le concepteur et le professorat pour les chemins de fer électriques de l‘Université technique de Dresde ont étudié ensemble les coûts du cycle de vie d‘installations de caténaire utilisant ce nouveau type de fil de contact. Les résultats de calculs comparatifs des variantes ont démontré que par l‘utilisation du nouveau fil de contact VALTHERMO peuvent être atteints des avantages économiques considérables pour les opérateurs de réseaux d‘installations de caténaire.

1 Introduction and motivation

Overhead contact lines ensure an efficient and reliable power supply for track-guided electrical transport sys-tems. The manufacturing and operating costs of over-head contact lines depend on numerous technical para meters, in addition to operational load. The type of contact wire used therefore has a significant influ-ence on the cost balance over the life cycle because it is the component of an overhead line which is suscep-tible to wear during its prolonged operational phase.

Electrolytic copper contact wires, the type most frequently used to date, must be replaced during sys-tem standing time, when wear limitations have been reached or when local damage makes replacement necessary. In special applications, copper contact wires alloyed with silver or magnesium are also used in order to increase mechanical strength. However, these are either more expensive or less electrically conductive.

The company nkt cables GmbH & Co. KG has developed a new, high-strength copper contact wire with the product name VALTHERMO®, which com-bines the advantages of good conductivity with those of high abrasion resistance and lower creep tendency.

Thanks to the increased standing time and a reduced need for readjustment, the new material significantly lowers costs in the operational phase, since it results in longer periods of time before contact wires need to be replaced. However, this is only reflected in the overall economic results when observed over an ap-propriately long period of time. An analysis of life cy-cle costs (LCC) is a suitable means of assessing these economic effects, with technical, operational and fi-nancial parameters taken into account.

The Chair for Electrical Railways at the Dresden Uni-versity of Technology has over recent years been very much concerned with the technical and economic as-pects of overhead line systems. This focus has involved questions about system design, mechanical and elec-trical strength of components and cost-effectiveness in the life cycle. On this basis, a scientific calculation tool has been developed in conjunction with nkt cables in order to enable LCC analysis of overhead line systems, with a particular focus on the application of various contact wire materials. This analysis tool is currently be-ing used to perform extensive tests for various applica-tions relating to local and long-distance transport, with variations in the operational and economic parameters.

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This article will first describe the material prop-erties of contact wires as well as the methodology behind and first results relating to life cycle costs, us-ing typical application scenarios. Once the results of ongoing field trials have been obtained, the findings relating to cost-effectiveness will be discussed in a later publication on the basis of further applications.

2 Material properties and results of a field trial on the DB network in Cologne

2.1 Material properties

Copper and low-alloyed copper are the materials used around the world for contact wires. These materials are particularly suitable for this application because of their corrosion behaviour as well as their electrical, thermal and mechanical properties, and they are standardised in [1]. With regard to mechanical requirements, tensile strength, hardness, resistance to wear, thermal expan-sion and creep properties are generally important crite-ria for the design of the contact lines, including the ad-ditional components required. In the copper materials that are typically used, the tensile strength and hardness required for the contact wires are achieved by means of cold forming through rolling and drawing, with strain hardening accompanying these processes. The basic material for the contact wires is normally a soft wire with multiple cross-sections, which can be produced us-ing a range of different manufacturing processes. The strength achieved by means of strain hardening must be maintained over the service life of the contact wire, oth-erwise the safety factors established as a basis for the sys-tem design cannot be adhered to. Alloy elements such as silver (Ag), magnesium (Mg) and tin (Sn) are used in low-alloyed copper in contact wires for a variety of reasons. All the elements listed here result in a significant improvement in the resistance of strain-hardened wires to softening due to recrystallisation at increased temper-atures. Mg and Sn also enhance the strengthening ef-fect, meaning that contact wires made from CuMg and CuSn alloys are also, depending on their composition, suitable for use in catenaries for high-speed transport (HST). See also [2; 3; 4]. Another important criterion when selecting materials is the creep resistance when mechanical tensile loads are applied under the increased temperatures that affect contact wires due to environ-mental conditions and heat generated by the electricity. Pure copper (Cu-ETP), which used frequently in contact wires nowadays, demonstrates relatively high levels of creep strain in practical applications. This leads to the need for costly and time-consuming readjustment of the catenaries within the first year after installation in or-der to ensure that the other components of the contact line are functioning properly and that the contact wire

is at the correct height. In contrast, using low-alloyed copper materials can render this kind of readjustment unnecessary because the creep strain of these alloys is typically only 25 – 40 % that of Cu-ETP under the same conditions. The enhanced creep properties of the alloys are due in large part to the improved thermal resist-ance to recrystallisation. To achieve thermal resistance, only small quantities of the alloying elements need to be added to the alloy. An additional advantage of this is that electrical conductivity does not have to be com-promised significantly. This is only the case when larger proportions of magnesium or tin, for example, are used in the alloys in order to produce contact wires with sig-nificantly increased tensile strength characteristics for use in high-speed transport.

The wear of the contact wires is influenced by nu-merous factors, a significant one of which is the con-tact wire material. In [3], measurements taken by DB for CuAg0.1 contact wires were compared with those taken by Russian Railways for Cu-ETP, concluding that contact lines made from silver alloys demonstrate a considerably longer service life. For this reason, and on account of the improved creep properties, CuAg0.1 contact wires are often used today for local and long-distance transport at speeds of up to 250 km/h. These materials have the same electrical conductivity as Cu-ETP – which is also the highest possible electrical conductivity.

In 2012, nkt cables developed the new material VALTHERMO, the objective of which was to at least match the positive properties of CuAg0.1 without the need to use silver, which is expensive and prone to vola-tile pricing. In order to make a comparison with Cu-ETP, CuAg0.1 and CuMg0.2, the material VALTHERMO was, in the form of an AC-100 contact wire, installed on a straight section of the long-distance track running from Cologne to Neuss [5] in 1400 m consecutive sections, and then tested. Wear and creep strain measurements were taken and then compared. The results of the creep strain comparison have already been published in [2]. VALTHERMO, CuAg0.1 and CuMg0.2 only demonstrat-ed 25 – 40 % of the creep strain exhibited by Cu-ETP.

2.2 Results of a field trial on the DB network in Cologne – Comparison of materials

Once development of the VALTHERMO contact wire was completed in early 2012, it was agreed with DB Netz AG that a field trial involving contact wires made from various materials would be conducted. The section run-ning between Cologne and Neuss was identified as a suitable installation location (Fig. 1, as per [5]). Contact line type Re160 is used here. After 25 years of use, the Cu-ETP AC-100 contact wire installed here had reached the wear limit specified by DB. The support cables and trailers did not show any signs of wear or fatigue, and were permitted to remain in the catenary.

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The reductions in contact wire diameter due to wear on all materials were identified at each of the seven comparable measuring points. Fig. 2 shows the average values of the contact wire diameter reduction in the case of Cu-ETP. This corresponds to 100 % of the average contact wire diameter reduction of Cu-ETP. It demon-strates the positive wear characteristics of VALTHERMO in comparison with pure copper and with CuAg0.1.

Fig. 3 compares the maximum contact wire diam-eter reductions in relation to Cu-ETP. The superior wear resistance of VALTHERMO was most pronounced at the most wear-intensive measuring point.

Thanks to the positive results of the field trial with regard to wear and creep characteristics, the con-tact wire material VALTHERMO was approved by DB Netz in August 2014 and has since been used in nu-merous projects as well as for maintaining local and long-distance transport routes.

3 Life cycle cost analysis

3.1 Methodology

To assess the cost-effectiveness of overhead line sys-tems using the new VALTHERMO contact wires in comparison with conventional materials, a life cycle cost analysis was carried out with typical technical, operational and economic parameters. To this end, example scenarios were prepared in order to not only investigate the areas of application of local and long-distance transport, but also reflecting the volume of traffic in terms of medium and high distributed load.

In an LCC analysis, all the costs associated with manufacturing, operation and disposal of a technical system are added together over the period of time

under review. Variants with comparable operational methods are assumed to offer the same economic ad-vantages – in the form of income from fares or freight revenues, for example – which means that that cost-effectiveness can be evaluated on the basis of costs alone. If additional revenues are collected from the resale of raw materials during disposal, for example, these are taken into consideration as in-payments.

Technical input variables such as quantity structures as well as current loads, and operational parameters such as train numbers and speeds, are also included in the calcula-tion. These parameters are linked to basic financial data such as initial values, payment dates, the rate of price in-creases and real interest rate. It is possible to make a mean-ingful comparison of the total costs determined in relation to specific observation times for the variants under review. An analysis of cost drivers is in this case unnecessary.

Because the overall cost-effectiveness of the elec-trification scenarios under review is specified with the corresponding quantity structures, a differential calcu-lation of the capitalised values from the LCC analysis can be carried out for various contact-wire materials on the basis of costs.

In each case referred to here, the cost differences were based on a kilometre of double-tracked section of rail in order to illustrate the results. This makes it possi-ble to show the accrual of cost benefits over time.

Reliable basic technical and operational data, as well as substantiated estimates of long-term economic pa-rameters, are essential for ensuring that any given LCC analysis can be meaningfully interpreted, since these fac-tors have a considerable influence on the result. Where the technical and operational data was concerned in this case, extensive research was conducted with the involve-ment of system operators. For the economic parameters, meanwhile, long-term statistical data was analysed.

3.2 Investigation scenarios

3.2.1 Local and long-distance transport applications

The life cycle costs analysis was carried out• in the case of contact wires in overhead lines

for long-distance heavy rail transport with alternating current, and

• in the case of contact wires for local light rail transport with direct current.

This was due to the different ways in which the two scenarios experience wear, something which is influ-enced by the frequency and speed at which the track is used, as well as by current loads.

For both basic scenarios, estimates were defined for the technical parameters of the overhead lines, for operational loads, for contact wire wear and for the re-sources required to perform maintenance measures. In

Figure 1:Installation location of the testing lengths in the DB network field trial on the Cologne/Neuss route [5].

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order to reflect the influence of the distributed load on contact wire wear and, therefore, the costs associated with maintenance and energy losses, all calculations were carried out for a conventional, medium distrib-uted load and for a high distributed load.

3.2.2 Technical and operational parameters

Assumptions were defined for the conventional load and high load scenarios, as shown in Table 1.

The corresponding wear values were established on the basis of defined load scenarios, with the ser-vice life calculated under the assumption of a linear cross-section reduction as per [4; 6]. For this purpose, a constant daily train path number was assigned over the entire period under review.

The wear characteristics of a contact wire depend on numerous influencing variables, which are de-scribed in the literature [6; 7; 8] and in scientific works [9]. Due to the many influencing factors that alter dur-ing the service life, it is not possible to predict actual wear measurements with any accuracy. The maximum loss amounts of the first measurements that applied at that point in time were converted into equivalent loss cross-sections in accordance with [7] and the wear rate was determined on the basis of the load spectra. In the case of electrolytic copper, similar wear rates were produced as per [6; 10; 11].

It was only possible to derive the service life of a contact wire in local transport based on empirical studies. In this case, the cross-section is initially re-duced to the furthest possible extent at hard points when there are accumulations of mass, within accel-eration ranges of vehicles with a high current load, and at fault sites; the critical contact wire height is reached as a result, necessitating replacement of the contact wire. According to the literature, standing times of the contact wires made from Cu-ETP in the case of local transport are specified as between 20 and 30 years in Germany [8]. A scientific investiga-tion carried out at the Dresden University of Technol-ogy demonstrated service lives of between 31 and 44 years at the specified wear-intensive sections of the contact line in an analysis of a sample local-transport network; this involved 600 V nominal voltage with 5 to 10-minute cycle operation and a contact wire cross-section of 100 and 120 mm2 [12]. On the basis of this, a 30-year service life is assumed for the con-ventional load scenario according to Table 1, with a 120 mm2 nominal cross-section. The extent of wear is determined in accordance with the linear cross-sec-tion reduction procedure that has been explained. In the case of local transport, the same wear ratio was initially estimated for the materials under investiga-tion as in the case of long-distance transport. It will be possible to vary the wear rates accordingly for any further investigations that are carried out.

3.2.3 Economic assumptions

In order to determine costs accurately over the long service life of an overhead line system, life cycle cost cal-culations are based on the method of dynamic capital budgeting. The capitalised value method represents the most suitable form of the calculation procedure, which is also based on empirical studies and recommenda-tions of standards regarding life cycle considerations [13; 14]. The cost elements are itemised according to the life cycle phases before use, during use and after use in accordance with the European standard EN 60300-3-3 [14] and the VDI guideline 2884 [15].

The service life of an overhead line system is influ-enced heavily by the standing time of the masts and foundations. A period of 70 years was selected for the LCC analysis, based on [16] and [4]. To simplify the cal-culation, only the components of the catenary are taken

Figure 2:Comparison of the average contact wire diameter reduction relative to Cu-ETP (AC-100 design, average relative contact wire diameter reduction of Cu-ETP 100%, equates to Δd).

Figure 3:Comparison of the maximum contact wire diameter reduction at the measuring point with the greatest wear in each case, relative to Cu-ETP (AC-100 design, average relative contact wire diameter reduction of Cu-ETP 100%, equates to Δd).

0

20

40

60

80

100

120

CuAg0,1 Valthermo Cu-ETP

Δd

%

0

50

100

150

200

250

300

CuAg0,1 Valthermo Cu-ETP

Δd

%

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Overhead Contact Lines

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into consideration, since a differential analysis requires the overhead lines being compared to be different from one another with respect to these components only. This makes it unnecessary to record the identical costs for the foundations, masts, cantilevers and track earthings.

The capitalised value KW of a variant used in a com-parison is calculated from the sum of the cash equiva-lents of returns plus the cash equivalent of the liquida-tion proceeds at the end of the period under review, minus the initial outlay set at zero for the investment in the year under review, based on the equation (1).

whereKW Capitalised value in €AZ0 Initial net investment at time t = 0 years in €EZt In-payment at time t in €AZt Payment / costs at time t in €γ Price increase rate in %in Nominal interest rate in %i Required rate of interest in %t time in aRWLD Residual value at the end of the period

under review (liquidation proceeds) in €LD End of the period under review

(life cycle duration) in aBWRF Cash equivalent of returns in €BWRW Cash equivalent of residual value in €

3.3 Payment sequences under review

In the period under review, the following payment sequences are recorded on the basis of how they are assigned to the life cycle phase of the contact wire. During the investigation, the maintenance costs were considered on the basis of the applicable guidelines, the technical literature and the experi-ence previously gained by the operators.• Payment sequences before use:

– Initial net investment: Costs of materials, per-sonnel, machine use and operational obstacles

• Payment sequences during use: – Wear-dependent costs associated with energy

losses due to cross-section alteration – Costs for preventive maintenance measures:

readjustment of personnel, machine use and operational obstacle costs

– Costs for preventive maintenance measures: contact wire diameter measurement: person-nel and machine use costs

• Payment sequences after use – Costs for corrective maintenance measures: con-

tact wire replacement: Costs of materials, per-sonnel, machine use and operational obstacles

– Material residual value with corrective mainte-nance measure: contact wire replacement

• End of period under review – Material residual value as liquidation proceeds

Other incomes arising from the operation of the transport system are disregarded because it is as-sumed that such incomes remain the same under all alternative scenarios relating to the investments being compared, based on the principle of equal income se-quences [13]. The payments represent the capitalised value. The difference between the calculated capital-ised values over 70 years reflects the advantage of the new VALTHERMO contact wire compared with contact wires made from Cu-ETP or CuAg0.1.

4 Results of the LCC analysis

4.1 Long-distance transport

Fig. 4 shows the cost advantage, as per the initial esti-mates, of the VALTHERMO contact wire for a kilometre of double-tracked section of rail, based on the convention-al and high load scenarios in long-distance transport.

Compared with the material Cu-ETP, a life cycle cost advantage totalling EUR 70,000 per kilometre of double-tracked section of rail can be achieved at the end of the period under review in a conventional load scenario (Fig. 4; dark-blue characteristic curve). Given the need to replace Cu-ETP multiple times, the life cycle cost advantage of the VALTHERMO contact wire is much more favourable. Moreover, a Cu-ETP contact wire replacement makes it necessary to carry out readjustments within the first year after instal-lation. This cost factor is reflected in the character-istic curve. When comparing the life cycle costs of the VALTHERMO contact wire with those of the cop-per alloy CuAg0.1 version, a small advantage can be seen in the new contact wire of approximately EUR 5000 per kilometre of double-tracked section of rail (Fig. 4; red characteristic curve). As per the initial estimates, this advantage is essentially generated by means of savings in energy loss costs in the during use life cycle phase.

KW = AZ0 + BWRF + BWRW

BWRF = EZt AZt( ) 1+r

100

t

1+in

100

t

t=1

LD= EZt AZt( ) 1+

i100

t

t=1

LD

BWRW = RWLD 1+r

100

LD

1+in

100

LD

= RWLD 1+i

100

LD

where(1)

(1.1)

(1.3)

KW = AZ0 + BWRF + BWRW

BWRF = EZt AZt( ) 1+r

100

t

1+in

100

t

t=1

LD= EZt AZt( ) 1+

i100

t

t=1

LD

BWRW = RWLD 1+r

100

LD

1+in

100

LD

= RWLD 1+i

100

LD

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In the high load scenario involving the VALTHER-MO contact wire, a life cycle cost advantage of EUR 150,000 per kilometre of double-tracked sec-tion of rail can be achieved compared with the conventional Cu-ETP contact wire, and EUR 20,000 per kilometre compared with the CuAg0.1 con-tact wire. This relationship is represented in Fig. 4 by the light-blue and orange characteristic curves. This represents a significant increase in the capital-forming advantage compared to the conventional load scenario. Because of the increase in the rate of wear resulting from the change in operational load, it is necessary to replace a Cu-ETP contact wire after just 14 years, a CuAg0.1 wire after 41 years and a VALTHERMO wire after 72 years. Only a setup includ-ing the new VALTHERMO contact wire would not require any corrective maintenance measures. The additional readjustment associated with replacing the Cu-ETP wire within the first year after installa-tion increases the life cycle cost advantage of the VALTHERMO contact wire.

4.2 Local transport

A life cycle cost advantage can also be generated for local transport by using the VALTHERMO contact wire. Fig. 5 shows the accrual of the LCC advantage over time in the case of conventional and high load scenarios for local transport.

In the conventional load scenario, and with the de-fined parameters applied, a high life cycle cost advan-tage totalling EUR 130,000 per kilometre of double-tracked section of rail can be seen compared with the contact-wire material Cu-ETP. In Fig. 5, this corresponds to the dark-blue characteristic curve. When comparing the life cycle costs of the VALTHERMO contact wire with those of the copper alloy CuAg0.1 version, a specific advantage can be seen in the new material of almost EUR 20,000 per kilometre of double-tracked section of rail (Fig. 5; red characteristic curve).

In the high load scenario in local transport, a high life cycle cost advantage of the VALTHERMO contact wire is calculated at approximately EUR 230,000 per kilometre of double-tracked section of rail compared with using the Cu-ETP contact wire, in line with

TABLE 1

Technical and operational quantity structure of the tested scenarios.

Long-distance transport Local transport

Traction power system 15 kV AC, 16.7 Hz 750 V DC

Overhead line design Catenary system Catenary system

Contact wire Ri100 AC-120

Section length 50 km, double-tracked 5 km, double-tracked

Conventional load scenario ≈7.5 min cycle at 20 h operating time 5 min cycle at 20 h operating time

High load scenario ≈3.5 min cycle at 20 h operating time 2.5 min cycle at 20 h operating time

Figure 5:Life cycle cost advantage ΔKW of VALTHERMO compared with Cu-ETP and CuAg0.1 for the conventional load and high load scenarios in local transport.1 Conventional load scenario, VALTHERMO compared with Cu-ETP2 Conventional load scenario, VALTHERMO compared with Cu-Ag0.13 High load scenario, VALTHERMO compared with Cu-ETP4 High load scenario, VALTHERMO compared with Cu-Ag0.1

0

50

100

150

200

250

300

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

ΔKW

t

TEUR/km

a

1

2

3

4

Figure 4:Life cycle cost advantage ΔKW of VALTHERMO compared with Cu-ETP and CuAg0.1 for conventional load and high load scenarios in long-distance transport.1 Conventional load scenario, VALTHERMO compared with Cu-ETP2 Conventional load scenario, VALTHERMO compared with Cu-Ag0.13 High load scenario, VALTHERMO compared with Cu-ETP4 High load scenario, VALTHERMO compared with Cu-Ag0.1

0

50

100

150

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

ΔKW

ta

TEUR/km

3

1

4

2

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initial estimates. This is considerably higher than in the conventional load scenario because a contact wire made from Cu-ETP must be replaced four times. In Fig. 5, the specified LCC advantage of the VALTHERMO contact wire corresponds to the light-blue characteristic curve. Com-pared with a CuAg0.1 alloy contact wire, the life cycle cost advantage amounts to EUR 25,000 per kilometre of double-tracked section of rail. In direct comparison with the conventional load scenario, the increase in the advantage is lower because the cross-section reduction starting from the point at which the CuAg0.1 wire is re-placed leads to higher costs associated with energy losses in the case of the VALTHERMO contact wire, as is evident from the decreasing orange characteristic curve in Fig. 5, starting from year 4. Nevertheless, the savings generated over the entire period under review in terms of costs as-sociated with energy losses constitute an advantage.

Once the results of further field trials have been ob-tained, the life cycle costs analyses will be extended to include additional variants, and the results will be pub-lished in this periodical.

References[1] EN 50149:2013-02: Railway applications – Fixed installa-

tions – Electric traction – Copper and copper alloy grooved contact wires.

[2] Hayoz, P.; Wili, U.; Rogler, R.; Kitzrow, G.; Pupke, F.: Fahrdrahtschäden in Streckentrennungen – Härte und Zug-festigkeit [Contact wire damage in insulated overlaps – Hard-ness and tensile strength]. In: Elektrische Bahnen 112 (2014), Issue 4, p. 207–213.

[3] Kießling, F.; Puschmann, R.; Schmieder, A.; Schmidt, P.: Fahrleitung elektrischer Bahnen – Planung, Berechnung, Ausführung [Con-tact lines for electrical railways – planning, calculation, execu-tion]. B. G. Teubner Verlag, Stuttgart – Leipzig, 2nd ed., 1998.

[4] Kießling, F.; Puschmann, R.; Schmieder, A.: Fahrleitungen elek-trischer Bahnen. Planung, Berechnung, Ausführung [Contact lines for electrical railways. Planning, calculation, execution]. Publics Publishing Verlag, Erlangen, 3rd ed., 2014.

[5] DB Netz AG: infrastruktur.geodaten@deutschebahn.com, dated 2015.

[6] Kasperowski, O.: Kontaktwerkstoffe für Stromabnehmer ele-ktrischer Fahrzeuge [Contact materials for pantographs of electric vehicles]. In: Elektrische Bahnen 34 (1963), Issue 8, p. 170–182.

[7] Borgwardt, H.: Verschleißverhalten des Fahrdrahtes der Re-geloberleitungen der Deutschen Bundesbahn [Wear char-acteristics of contact wire used in standard overhead lines on the German railway network]. In: Elektrische Bahnen 87 (1989), Issue 10, p. 287–294.

[8] Besier, S.: Tragseillose Oberleitungen im Stadtverkehr?– Teil 2 [Overhead lines without support cables in urban transport? – Part 2]. In: Elektrische Bahnen 107 (2009), Issue 6, p. 257–266.

[9] Pintscher, F.: Dissertation: Kontaktvorgänge und Verschleißver-halten des Systems Fahrdraht-Schleifleiste [Contact processes and wear characteristics of the contact wire / contact strip system]. Dresden University of Technology, Friedrich List Fac-ulty of Transportation Science, Dresden, 2003.

[10] Alsalamat, H.: Dissertation: Verfahren zur Ermittlung des Einflusses von infrastrukturellen und betrieblichen Faktor-en auf die spezifischen Kosten der Eisenbahninfrastruktur [Method for determining the influence of infrastructural and operational factors on the specific costs of railway in-frastructure]. Dresden University of Technology, Friedrich List Faculty of Transportation Science. Dresden, 2011.

[11] Auditeau, G.; Avronsart, S.; Courtois, C.; Krötz, W.: Carbon contact strip materials –Testing of wear. In: Elektrische Bahnen 11 (2013), Issue 3, p. 186–195.

[12] Stöbe, T.: Thesis: Analyse der Einflussgrößen auf den Verschleiß von Fahrdrähten bei Stadt- und Straßenbahnen [Analysis of the variables influencing the wear of contact wires in light rail and trams]. Dresden University of Technology, Friedrich List Faculty of Transportation Science, Dresden, 2010.

[13] Blohm, H.; Lüdner, K.; Schaefer, C.: Investition. Schwachstel-lenanalyse des Investitionsbereichs und Investitionsrechnung [Investment. Vulnerability analysis of the investment field and capital budgeting]. Verlag Franz Vahlen, Munich, 10th ed., 2012.

[14] EN 60300-3-3:2005: Dependability management – Part 3-3: Application guide – Life cycle costing.

[15] VDI 2884:2005: Purchase, operating and maintenance of production equipment using Life Cycle Costing (LCC).

[16] Schneider, F.; Lerner, F.: Ökonomisch orientiertes Gütekriterium für das System Oberleitung – Stromabnehmer [Economically oriented quality factor for the overhead line / pantograph sys-tem]. In: Zeitschrift für Eisenbahnwesen und Verkehrstechnik (ZEV) Glasers Annalen, 105 (1981), Issue 9, p. 265–270.

The German original paper was published in eb – Elektrische Bahnen 114 (2016), Iss. 4, pp. 188–195.

AUTHORS

Elisabeth Helwig (27) studied Transport Engineering at the Friedrich List Faculty of Transportation Science at the Dres-den University of Technology, specialising in Planning and Operating of Electrical Transportation Systems. Since 2014 she has been a scientific assistant at the Chair for Electrical Railways at the Dresden University of Technology.

Address: Dresden University of Technology, Friedrich List Fac-ulty of Transportation Science, Chair for Electrical Railways,01062 Dresden, Germany; Tel.: +49 (0) 351 463-36577;E-mail: elisabeth.helwig@tu-dresden.de

Prof. Dr.-Ing. Arnd Stephan (51), studied Electrical Engineer-ing/Electrical Railways at the Freidrich List University of Transporta-tion (HfV) in Dresden; 1990 to 1993: research course at the HfV/Dresden University of Technology; received Dr.-Ing. qualification in 1995; 1993 to 2008: at IFB – Institut für Bahntechnik GmbH (In-stitute of Railway Technology), Dresden; from 1995: branch man-ager of IFB Dresden; 1995: specialist in electrotechnical systems at the German Federal Railway Authority; from 1999: specialist in magnetic rail systems and, from 2015, in inverters; 2002: honorary professor at the Dresden University of Technology; from 2008: pro-fessor of Electrical Railways at the Dresden University of Technol-ogy; from 2012: Managing Director of IFB Berlin and Dresden.

Address: as above; Tel.: +49 (0) 351 463-36730;E-mail: arnd.stephan@tu-dresden.de

Dr.-Ing. Frank Pupke, (56) studied physics with a focus on in solid-state physics at the Technische Universität Magdeburg (Magdeburg University of Applied Sciences); 1984 to 1990: devel-opment engineer at MKM Mansfelder Kupfer und Messing GmbH in Hettstedt; from 1991: responsible for the metal industry and, from 2001 to 2004, for the continuous cast wire rod and wire busi-ness areas. 1990: PhD in materials sciences at the Freiberg University of Technology and Mining Academy. Since 2005: Head Engineer at nkt cables GmbH in Cologne, responsible for developing railway materials and metal products produced by the nkt cables Group.

Address: nkt cables GmbH, Produktentwicklung Material, Düsseldorfer Straße 400, Im Chempark, 51061 Cologne, Germany; Tel.: +49 (0) 221 676-2750; E-mail: frank.pupke@nktcables.com