Introduction to Rigid Overhead Conductor-rail System (ROCS)

The overhead conductor rail system is a kind of overhead power-feeding lines containing a rigid conductor rail placed over the vehicle, connected to the supporting structures or to the tunnel or subway tracks ceilings using a set of clamps and supports. Overhead conductor rail can be made in form of a U-shaped aluminum hollow profile with an open carter below it for inserting the contact wire, or in form of a solid copper profile.

The first overhead conductor rail system has been installed in 1984 in Zurich and it’s still operated with no need to maintenance operations until now.

Necessity and advantages of lines containing overhead conductor rail

The overhead conductor rail is essentially designed for use in short spaces over the vehicle in tunnels and under bridges, movable bridges and also for use in depots and vehicle repair and maintenance workshops. This rail gets place under tunnel soffits and structures and is a cost-effective, more compactable and reliable alternative for other overhead contact lines. Demand increase for an overhead system with high levels of safety, reliability, electrical load carrying capacity, short-circuit resistance and low construction height, requires creative solutions and “Rigid Overhead Conductor-rail System” so called ROCS is one of them. Absence of tensile force along contact wire, less component numbers and high resistance to fire, have made the overhead conductor rail as a safe and reliable solution in subway tunnel lines.

A most outstanding specification of using overhead conductor rail in tunnels and subway lines for constructors and clients, is the ability to design tunnels with less ceiling heights and less boring diameters. So that, by designing a tunnel or subway line containing an overhead conductor rail instead of traditional OCS, the boring diameters could be reduced up to about 2 meters.

Also the overhead conductor rail could be used in portions of lines in depots and workshops having retractable sections, for easier access and inspection of vehicle with no obstacles. Retractable overhead conductor rail, also could be used in loading and unloading equipment on movable bridges. In addition, retractable conductor rails could be used as charging port for electrically driving vehicles and hybrid buses.

ROCS has limited sagging and there’s no uplift for contact wire. Based upon that, the design height of contact wire will be lower compared with traditional OCS and the pantograph uplift disappears; the reason for fewer space requirements at tunnel soffits and under the bridges.

Comparing ROCS with conventional OCS

  • Lower design and installation height compared with conventional OCS lines and trolley-type lines (for example, 600 mm for AC 25 kV systems) so, the ability for tunnel construction with smaller diameters is provided, and as a result, the tunnel construction costs will be reduced.
  • Simplification of safety measurements for earthing of tensioning system by eliminating of the overhead line sectioning.
  • Eliminating the tensioning device for contact wires and catenary wires.
  • Simpler design due to the fewer components (approximately 10 times less components than OCS).
  • Long service life-time due to the high levels of allowable contact wire abrasion (because the contact wire is not in tension and can be worn more about 43 percent compared to OCS).
  • Higher current-carrying capacity (e.g. 3500 A with AC-150 contact wire clamped) and higher short-circuit resistance of the overhead conductor rail. Because of large conductor cross-sections, there is no need to additional feeder wires.
  • Reduced voltage drop compared with conventional OCS with a single contact wire and a catenary suspension.
  • High strength material selection for extruded profiles and clamping components and fittings.
  • Stable and vibration resistant joints by adopting longitudinal guide grooves and bolt locking devices.
  • Higher fire resistance compared with typical OCS lines.
  • Much more operational reliability and less maintenance operation requirements, regardless of operational voltage.
  • Faster installation speed, simplicity of storage and need to less spare parts.

Alucast Iran abilities in designing, manufacturing and installation of ROCS

According to the advantages mentioned above, also due to the extension of public transportation fleet in metropolitan and large cities, the discussion of deployment of a transportation system arises, which could be used in subway lines and could be justified in terms of safety and economic efficiency. Relying on experiences obtained in designing, manufacturing and installation of Overhead Catenary Systems (OCS) and related equipment at several projects, also considering the extension of demands for Rigid Overhead Conductor-rail Systems (ROCS) in railway projects of Islamic Republic of Iran, Alucast Iran has entered into the field of rigid overhead networks, and after passing through the research phase, has entered into the design phase of ROCS lines and manufacturing of the overhead conductor rail and related fittings and equipment.

An overhead rigid conductor rail line has less components compared with traditional OCS, due to its simplicity. All the components and equipment required for an overhead conductor rail line are designed and manufactured in Alucast Iran Co. At first step, the ROCS components and equipment are modeled in a professional CAD software by mechanical design team. Afterwards, the designed components are analyzed in terms of conformity of the mechanical and electrical properties with related standards, by mechanical and electrical analysis teams respectively. At the final step of designing of the components, they are experimentally tested to evaluate that the design process is correct.

After designing the system part by part, several configurations and arrangements of ROCS equipment are determined according to client and line requirements, and various supports and structures are selected based on them.

Afterwards, the loads applied on various components are obtained and calculated by analyses teams based on using circumstances in lines, such as span length, ceiling height, support type and so on, also based on the latest related standards and codes. After calculating the loads and determining the required materials, the mechanical numerical analysis is carried out under obtained loads by applying the recommended standards safety factors using the professional CAE software, to make sure that the components have correct behavior under the intended loadings.

Furthermore, performance of these components are electrically checked by Alucast Iran electrical engineering team. Electrical loads required for electrical analyzing of the components are obtained based on the latest standards and codes. Then, the components are numerically loaded in professional electrical analysis software and the electrical performance of the components are evaluated. Also, the Alucast Iran electrical engineering team decides on connection types, selection of type and capacity of the electrical connections, insulators, standard clearances between current-carrying components and others, design and determining the locations of earthing equipment, the lengths of electrical sections and other requirements based on global standards and the final stage at designing the line is carried out by interacting both mechanical engineering and electrical engineering teams.

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