Overhead line construction

Catenary in Austria
Catenary in Austria
© Plasser & Theurer

When new rail routes are built today they are all built with overhead electrified lines. Throughout Europe, almost all new railways are electrified - each one is a major project, regardless of whether it is a new railway trunk route, or a new tram line. Regardless of whether there are tight curves or a maximum line speed of 350 km/h, each element of the overhead line design and every phase of its construction is of great importance. The same applies for existing railway lines which have to be electrified. Complete modernisation or conversion of existing routes and overhead line systems can require a completely new design of catenary. For this purpose, highly specialised methods and effective techniques are used today. The vehicles mentioned here as an example can be found in many countries.

Traditional overhead line construction

In long-standing procedures, the masts were first set up and transverse beams fitted, then carrying cable and contact wire were separately fitted and individually tensioned. This pre-tensioning, together with the following quiet phase (“stretching pause”) before further assembly work, also serves to eliminate corrugations and other uneveness from the wires previously wrapped round a drum and to get the length equalisation. Assembly work was carried out from simple, rail mounted ladders, with scaffolding wagons, working platforms or other auxiliary vehicles, and not necessarily in the economically most reasonable sequence. Re-tensioning is required, sometimes even more than once. A consistent, high processing quality is thus hard to achieve. In addition, there are safety risks for the staff employed, at least, this is the case with the contact wire which is usually at a height of 4.95 to 6.5 m above the top of rail, and the tops of masts can easily be more than 10 m high.  

Planning and Projecting

Catenary in Austria with overhead contact wire, carrying cable and insulators
Catenary in Austria with overhead contact wire, carrying cable and insulators
© Plasser & Theurer

Economic overhead line construction begins at the project and planning phase, in which all work to be done can be seen as part of the total process, divided into individual steps. Although the legal, operational and technical requirements cannot be changed, an economic advantage can be achieved by the choice of working procedures, both in terms of quality, in time and ultimately also in financial terms. For example, possessions of subsequent sections can be significantly shorter. If the best possible work quality is obtained during construction and assembly, this in turn ensures long term route availability.

Placing the catenary masts

Unless they are already available and can be used further (in the case of a renewal), the construction of a new overhead line system begins with the construction of the mast foundations and the subsequent setting up of the catenary masts. Today, modern, efficient mast erection equipment is available. Steel mesh or spun concrete masts are normally used, which are ready for assembly.  

Fixtures and steady arms

First fastening elements, insulators and steady arms are fitted on the masts for the overhead contact wire, and depending on the catenary design also cross spans, as are used in Switzerland ("yokes") or to span several tracks. The mast-tops are available if required, to carry the supply lines and the earth or return conductor.    

Placing the catenary masts

Unless they are already available and can be used further (in the case of a renewal), the construction of a new overhead line system begins with the construction of the mast foundations and the subsequent setting up of the catenary masts. Today, modern, efficient mast erection equipment is available. Steel mesh or spun concrete masts are normally used, which are prepared for the assembly. 

Fixtures and steady arms

Overhead line construction and maintenance through modern CWRM
Overhead line construction and maintenance through modern CWRM
© Plasser & Theurer

First fastening elements, insulators and steady arms are fitted on the masts for the overhead contact wire, and depending on the catenary design also cross spans, as are used in Switzerland ("yokes") or to span several tracks. The mast-tops are available if required, to carry the supply lines and the earth or return conductor.

Carrying cable and contact wire

Overhead line construction and maintenance through modern CWRM
Overhead line construction and maintenance through modern CWRM
© Plasser & Theurer

The next step fits the actual contact wire and the carrying cable as well as the droppers and other wires together. Modern contact wire replacement machines (CWRM) unwind both wires at the same time from separate tilting drums (from two identical winding units with friction winches and drum tensioning devices) hinged drum plants (two identical winding units with friction winches and drum clamping). Both wires are laid at the same time with the final mechanical tension that is necessary for operation by means of hydraulic height adjustable lifting masts. The contact wire is delivered wave-reduced and warp-free in a zigzag course. 

Contact wire and carrying cable holding device support the positioning. Once the catenary has been installed it is necessary to manually align and fix the steady arms, droppers, trims and continuity jumpers. Finally, the position of the contact wire is technically checked.

Quality through technologies

During the construction and renewal of overhead line systems it is in the interest of a long useful life and low life cycle costs (LCC) to pay particular attention to the material. Stresses and tension fluctuations can reduce the service life, too great a contact wire ripple and position deviations can affect the interplay with the pantograph and lead to voltage breaks, sparks and damage. Modern contact wire renewal trains ensure the exact feed, position and tension of the contact wire, for a long period in service. The overhead line installed by such units consisting of several motorised tower wagons and the CWRM can be used in service immediately after the completion of the work.


You can find suitable specialist literature to the topic here:

Infrastructure Projects 2018

Infrastructure Projects 2018

How can we remove and rebuild rail infrastructure faster and better? - That's what the more than 30 papers in this book are about. Levers for faster and better implementation of projects are the acceleration and simplification of approval procedures as well as lean concepts in the construction industry, the introduction of the BIM method and partnership building. Using the example of the metropolitan areas of Berlin, Frankfurt and Munich, this book outlines which challenges population growth and disproportionately increasing economic performance mean for the transport infrastructure and how the transport networks can be made future-proof.

The Basic Principles of Mechanised Track Maintenance

The Basic Principles of Mechanised Track Maintenance

This book is dedicated to the many people involved in the day to day planning and performance of track maintenance activities. Providing a practical approach to everyday challenges in mechanised track maintenance, it is not just intended as a theoretical approach to the track system. 
Railways aim at transporting people and freight safely, rapidly, regularly, comfortably and on time from one place to another. This book is directed to track infrastructure departments contributing to the above objective by ensuring the track infrastructure’s reliability, availability, maintainability and safety – denoted by the acronym RAMS. Regular, effective and affordable track maintenance enable RAMS to be achieved.