Comprehensive overhead-line inspection

Posted: 3 December 2008 | | No comments yet

How the modern contacting and contactless inspection and analysis of overhead-line systems on normal and high-speed routes are a guarantee of safe railway operation without disturbances.

How the modern contacting and contactless inspection and analysis of overhead-line systems on normal and high-speed routes are a guarantee of safe railway operation without disturbances.

The modern contacting and contactless inspection and analysis of overhead-line systems on normal and high-speed routes are a guarantee of safe railway operation without disturbances.

At speeds of up to 160km/h, the vehicles of the Eurailscout infrastructure monitoring fleet can perform a complete recording of overhead-line systems. The various vehicles are equipped with state-of-the-art measuring and diagnostic systems which can monitor all aspects of overhead-line inspection.

The integrated observation and evaluation of the various parameters within the framework of a measuring run and the combination with measurements of other infrastructural data, provides considerable advantages and cost savings when compared to traditional inspection methods.

Measuring and inspection systems

Catenary-wire position measurement

Contactless laser systems determine the height and stagger of up to four overhead-lines, already corrected by the separately recorded sway movements of the vehicle body. The measurement can take place either charged (pantograph in the operating position – contact pressure can be altered according to the type of overhead-line construction) or uncharged. A contact force measurement can also be undertaken with the lifted pantograph.

Contact force measurement

With the lifted pantograph, the static and dynamic interactions of the pantograph and overhead-line are recorded by power and acceleration sensors. Determining the changing forces between the pantograph and overhead-line essentially helps in the search for defects in the catenary system. Special sensors in the external areas of the pantograph wearing-strip examine the position of incoming, outgoing and crossing sections of overhead-line equipment.

Measurement of the overhead-line strength

To determine the abrasion of the overhead-line, continuous contactless pictures of the overhead-line are taken by two sensors. The evaluation of the image material takes place with regard to the pantograph area width and the visible diameter. The image material upon which the evaluation is based is stored parallel to the measurement results. In this way, unclear situations can be inspected in tracking, without requiring inspections of the system on location, for example:

  • Determination of the remaining height of the overhead-line every 25cm with an exactitude of 0.25mm at 120km/h via the contactless pictures of the pantograph surface and the diameter of the overhead-line
  • Online determination of weak spots (areas with increased wear)

Determination of the positions of the catenary masts

The position of the masts along the routes being monitored is automatically recognised by laser-based systems and stored together with the measurement and inspection data. These sites are included in the corresponding evaluations.
The mast recognition system consists of two recording units, installed to the left and the right on the roof of the measurement vehicle above the bogies. Each recording unit consists of two laser-remote sensors. The measurement beam of the remote sensor is directed vertically. If the two laser beams of a recording unit are almost simultaneously reflected by an object, one may assume that it is a lateral support and thus an overhead-line checkpoint.

Video recordings

A special camera on the roof, complementary to the inspection systems introduced below, delivers high-resolution pictures from the pantograph and overhead-line system.

Digital cameras on the front of the vehicle make high-resolution video recordings from the driver’s point of view which are directly stored on hard-discs without analogous signal transformation. These are available in high-definition quality, both as individual pictures and as film. The maintainer can utilise these to carry out an inspection of the environment if errors in the measurement and inspection are suspected. The individual pictures of the video are precisely linked with the track kilometrage, so that overhead-line defects can be directly linked to the corresponding picture from the monitored route.

Inspection of the longitudinal overhead-line equipment

Two high-speed diode line-scan cameras positioned to the outer edges of the vehicle, together with an infrared laser illumination, take continuous pictures of the opposite sides, tilted from below at 80km/h with 1mm resolution (45 µsec exposure time – data rate 100 MHz). The result is an ‘infinitely’ long picture of both sides of the longitudinal overhead line equipment. The pictures are precisely linked with the track kilometrage and with these high resolution pictures, a visual inspection at the screen is possible (monitoring) without any further processing. As a next step, these pictures can be prepared for an automatic evaluation.

Inspection of the cantilevers and registration arms

The recording of the cantilevers and registration arms is undertaken with high-speed line-scan cameras by two cross-member works sensors positioned on the ends of the vehicle, both with and against the direction of travel.
The front mast recognition system recognises the cantilevers and registration arms, thus activating the rear scanner system which ‘looks’ towards the front.

With consideration for the route already travelled, the front scanner system orientated towards the rear is then activated. This results in recordings of cantilevers and registration arms from both sides. The individual pictures are precisely linked with the track kilometrage. A visual inspection at the screen (monitoring) is then possible with these high-resolution pictures without any further processing. As a next step, these pictures can also be prepared for an automatic evaluation.

Automatic visual inspection

The automatic visual inspection is based upon the systems previously described. The four sensors in these systems produce approximately four gigabytes of image data per kilometre travelled; for ease of transmission this data is stored in a highly compressed format.

The automatic inspection of the complete overhead-line equipment takes place with automatic offline image processing through the automatic recognition of alterations. This is achieved by comparing a defined condition recording (learning run), with successive inspection runs. The reference data of the given route from the learning run is compared with the image data of the inspection run. Defects can be recognised in this manner and classified accordingly.

The real-time determination of the overhead-line altitude and lateral position, as well as the remaining overhead-line height, is completed by the offline image processing based upon the stored recordings.

The automatic image evaluation is carried out with the aim of recognising changes, damages and foreign bodies. The goal is the automatic detection of defects, such as, for example, loose or missing screws, spliced cables, damaged components or deviations in geometry.

Result Protocol: Location, Defect Class

All the geometric data of the overhead-line system described before is recorded every centimetre, displayed every 25cm and stored digitally. All measurement data can be shown on computer screens and printed out on paper during the inspection run. The layout of the diagrams (choice of conduits, curve position, scale, language, etc.) can be adjusted at short notice, in accordance with the client’s wishes. Complex analyses and reports in different languages have already been implemented for several clients (ProRail, DB AG, Network Rail, CTRL, SZ, etc.).

The results of the visual inspection can be made available in a data bank system. If required, an extended analysis of the results of the picture evaluation is offered for direct inclusion in the maintenance process.


The measurement vehicles of Eurailscout survey all infrastructural data necessary for a comprehensive analysis of the condition of the overhead line equipment, thus also providing the basis for a maintenance that can be planned in direct relation to the actual conditions.

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