online temperature monitoring of overhead contact line at the … · 2014-05-10 · contact line...

Online temperature monitoring of overhead contact line at the new German high-speed rail line Cologne-Rhine/Main

N. Theune, T. Bosselmann, J. Kaiser, M. Willsch, H. Hertsch & R. Puschmann Siemens AG, Corporate Technology, Germany

Abstract

This paper reports on the first fiber-optic temperature measurement of overhead contact line systems at a new ICE3 high speed line of the German Railway. The installation of Fiber Bragg Grating (FBG) sensors, the online acquisition and interrogation of data over a one year period is presented. Keywords: Fiber Bragg Grating, temperature monitoring, overhead contact line, catenary, power management.

1 Introduction

All railway companies try to achieve higher reliability and flexibility in train service. As a consequence the quality of train control processes as well as monitoring equipment for the next generation of high speed railway lines needs to be improved. Next generation of high speed trains will consume more power, because of an increased amount of electrical amenities inside the train and - of course - higher speeds of up to 300 km/h and more. This goal can only be achieved if the overhead contact lines that provide the energy for the trains are protected reliably from thermal overload caused by electrical overcurrents and hotspots at the catenary wire and contact wire. Up to now diagnostic systems for online acquisition of real temperature data do not exist. As a state of the art, conventional Digital Protection Devices (DPDs) in substations inhibit a simple numerical model from which the so-called catenary temperature is estimated with respect to current load and ambient air temperature [5]. If the estimated temperature exceeds a certain limit of e.g. T=70°C the power supply of the overhead contact line is switched off, regardless of the actual temperature on the

Power Supply System Analysis, Design and Planning 87

www.witpress.com, ISSN 1755-8336 (on-line) WIT Transactions on State of the Art in Science and Engineering, Vol 39, © 20 WIT Press10

doi:10.2495/978-1-84564- - /498 7 09

overhead contact line. If the actual temperature would be higher, thermal overusage of the overhead contact line system could destrengthen parts of the catenary construction. Furthermore elongation may cause a malfunction of a passing train pantograph or lead to a destruction of the contact wire. If the actual temperature would be lower than the limit, the power supply for the trains would be switched off needlessly. Both cases are connected to cost-intensive down time of the train line. In order to control reliably and adapt to the growing power needs for high speed trains and to use up to date overhead line systems more efficiently an accurate online determination of the overhead contact line and contact wire temperature is essential. The appropriate temperature sensors have to be compact, should be easily integrable in the catenary construction and must be able to measure on high voltages of up to 25 kV. In general conventional temperature monitoring techniques could be applied alternatively, but due to the high voltage level of the overhead line an enormous amount of effort needs to be put into the insulation of these sensors or into provision of independent power supplies etc. [1]. On the other hand FBG sensors offer, because of their vitreous nature, a simple way to measure on high voltages with a minimum of insulation material needed. Multiplexed temperature measurements with the help of FBGs could help to localize hot spots and provide a continuous measurement for the protection of the power line [3]. If the temperature distribution of a complicated network structure could be measured the required material effort of new installations could be optimized which would lead to substantial savings. Furthermore in peak-periods the power supply could be managed intelligently with respect to the actual thermal usage of the catenary. The measuring system, the multiplexed network of sensors and the sensor setup which were implemented on the new high speed rail line between Cologne and Frankfurt will be presented and discussed. In the future this technique can be easily adapted to similar applications of railway transportation systems e.g. long distance railways with overhead contact lines with still higher demands with respect to current load.

2 Theory

2.1 Brief theory of fiber Bragg gratings

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,

88 Power Supply, Energy Management and Catenary Problems


contribute to a center wavelength shift of the Bragg reflex. In case of the catenary temperature sensors the first effect needed to be excluded. This was done through a sensor design that decoupled any stress acting on the sensor housing, e.g. elongating electric wires, from the sensing FBG element. The thermal effect of current load on the overhead contact wires and the estimation of the so called catenary temperature will be discussed in the next section.

2.2 Model for numerical estimation of the catenary temperature

Nowadays the DPDs inside transformer substations evaluate the temperature of the catenary with the help of a simple numerical model. The electric current signal I and the ambient air temperature ambT are processed in an exponential function to compute the catenary temperature catT

( )2

max,ambcat

)(1)()(

⋅−⋅+=

∞

−∞ I

tIeTtTtT t τ , (2)

whereas ambT represents the ambient air temperature, ∞T the maximum excess temperature after ∞=t , τ the thermal constant of the catenary type, t the time, I the actual current and ∞max,I the maximum current after ∞=t . In practice, if the calculated catenary temperature catT exceeds 70°C the relay causes a power circuit breaker in the switch yard to switch off the current. The numerical model is uncertain, because various parameters are not accounted for, e.g. wind velocity, wind temperature, incident solar radiation, precipitation etc.

3 Measuring setup

The setup for online measurement of the catenary temperature is based on a polychromator interrogation unit, as in Figure 1:. The polychromator unit consists of a diffraction grating, a CCD array, an ADC card and a PC for online temperature evaluation of the spectral intensity information acquired from the CCD array. As a light source a broadband LED with a center wavelength of

nm840=λ and a full width at half maximum of nm45FWHM =λ∆ was used. As the whole interrogation unit was used in field, e.g. ambient temperatures were ranging from C10°− to C40°+ , an Argon calibration lamp was preferred to eliminate the temperature dependent shift in wavelength over CCD-pixel. The Argon spectral peaks between 800 and 850 nm were used as a reference in order to get a calibrated functional dependency between CCD-pixel and wavelength. A 4x1 fiber switch operated continuously between the 4 sensor channels. The whole setup consists of exchangeable card modules and was implemented into a portable 19-inch rack, as in Figure 3:.



Figure 1: Polychromator setup with Argon calibration lamp and 4x1 fiber switch.

Figure 2: Location of FBG temperature sensors on the overhead wires at the injection pylon – 300m apart from the Limburg transformer substation.

4 Application of sensors

Figure 2: shows the locations on the catenary where FBG sensors were installed. The sensors were manufactured in a single ended design that has been used also in other fields of high voltage applications, e.g. power generators [2], as redundancy for this first field demonstration in this delicate application was of major importance. Every single FBG sensor was provided with an individual optical link to the interrogation unit – located in the transformer substation -



m300 apart from the injection pylon. Two FBG sensors are installed in close

thermal contact to the two injection wires, each of 2mm240 cross sectional area. Further two FBG sensors are located at supporting current wires, each of

2mm120 cross sectional area. The signals of the four FBG sensors are then transformed into a temperature value. Simultaneously the catenary temperature signal provided by the DPD - also located inside the transformer substation – is calculated. Both data are then submitted - via a GSM link - to a control PC, over

km300 away, to our lab in Erlangen for analysis.

Figure 3: Left: Polychromator interrogation unit with online FBG temperature data, Right: DPD with online calculated catenary temperature data

5 Measurements

In Figure 4: the online catenary temperature data in 12/2002 and 01/2003 acquired from the DPD is shown. In Figure 4:(a) the overall current signal I with values up to kA2 at an effective voltage of kV5.16≈U @ Hz16 3

2 can be seen [4]. The measured ambient air temperatures ambT in (b) range from

C10°− to C10° . The calculated excess temperature T∆ , i.e. the temperature increase that is due to the current load, is shown in (c). In Figure 5: the online FBG sensor temperature data of the sensors 1 to 4 is shown. Overall the temperature data of the four FBG temperature sensors corresponds very well to the calculated data of the DPD. But in detail the differences between the fiber-optical and calculated data can be enormous. This will be shown and discussed in the next section.



Figure 4: DPD data between 11/2002 – 01/2003.

Figure 5: Signals of 4 FBG temperature sensors, installed on catenary wires.

6 Discussion of results

In Figure 6: the difference between FBG sensor #2 and the calculated DPD catenary temperature is plotted. It can be seen that the difference in temperature between the fiber-optical sensor at the catenary and the calculated DPD data can reach up to approx. C8° . If we zoom into the rectangular dashed part in Figure 6:, then a typical behavior of the FBG catenary sensor can be seen, as in Figure 7:. Here the optical sensor takes into account the incident solar radiation, i.e. due to the solar energy the catenary wire warms up over a period of several hours only interrupted through periods of cloudiness. At that day - after the sunset at around 16.30h - the influence of cold wind dominates and chills the catenary wire.



Figure 6: Temperature difference between FBG sensor #2 and the DPD temperature data.

Figure 7:

7 Conclusions

For the first time online temperature measurements with FBG temperature sensors on railway overhead lines could be demonstrated. All sensors measured successfully under outdoor conditions over a one year period. As a first experimental result it was found out that the excess temperatures due to current load are small compared to ambient sources of temperature

Zoom into the dashed rectangular part of Figure 6.



change. In the future this first result will be analyzed under different seasonal and current load conditions. In the future FBG sensors will be installed on other hotspot locations at the overhead contact line. The measurements indicate that there might be a large cost saving potential for similar future installations. FBG catenary sensors can provide catenary designers with real data acquired over several years and help optimize the construction system with respect to reduction of material expenses and optimization of the power management.

Acknowledgements

The authors thank sincerely Mr. Walter Weisel from German Rail Energy for his ongoing support during the whole project. Part of this work was financially supported by the National FAMOS project.

References

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

[2] Theune, N.M.; Müller, M.; Hertsch, H.; Kaiser, J.; Willsch, M.; Krämmer, P.; Bosselmann, T.: “Investigation of Stator Coil and Lead Temperatures on High Voltage inside Large Power Generators via use of Fiber Bragg Gratings”. IEEE Sensors 2002 Conference, Conference Proceedings, Orlando, USA.

[3] Bjerkan, L.: “Measurements of overhead transmission line loads with Bragg gratings”. Conference Proceedings, SPIE 3746, OFS-13, Kyongju, Korea, P2-27, 1999.

[4] 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.

[5] Digital Overhead Contact-Line Protection 7SA517, Instruction Manual, Edition 08/2001, Siemens AG.



online temperature monitoring of overhead contact line at the … · 2014-05-10 · contact line...

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