Overview and Construction
– Overhead lines are used to transmit electrical energy to electric locomotives, trolleybuses, or trams.
– Electric trains collect their current from overhead lines using devices like pantographs, bow collectors, or trolley poles.
– Non-electric locomotives can pass along these tracks without affecting the overhead line.
– Alternative electrical power transmission schemes for trains include third rail, ground-level power supply, batteries, and electromagnetic induction.
– Overhead lines are usually fed from a high-voltage electrical grid.
– Contact wires are supported by a second wire called the messenger wire or catenary.
– Droppers or drop wires connect the messenger wire to the contact wire at regular intervals.
– The pantograph’s carbon insert becomes worn over time and the contact wire is zigzagged to prevent notches.
– Tramways use a contact wire without a messenger wire.
– Modern systems use current-carrying droppers instead of separate wires for physical support.
Parallel overhead lines
– Trams and railways use the overhead line and steel rails as the conductors for the electrical circuit.
– Trolleybuses use a second parallel overhead line for the return current.
– Trolley poles are used to contact both overhead wires in trolleybuses.
– Pantographs are generally incompatible with parallel overhead lines.
– Some railways with three-phase AC electrification also use parallel overhead wires.
Types of wires
– Contact wires are made of cold drawn solid copper with grooves for hangers to attach.
– Messenger or catenary wires are multi-strand wires with strands made of copper, aluminum, and/or steel.
– Some wires have a steel core for strength, coated with an anti-corrosion substance.
– In Slovenia, contact wires are available in sizes of 100mm and 150mm, while catenary wires have sizes of 70mm, 120mm, or 150mm.
– Different configurations of contact and catenary wires are used for main lines and side tracks.
Tensioning and Brake Mechanisms
– Catenary wires are kept in mechanical tension to prevent standing waves and sag.
– Tensioning methods include weights or hydraulic tensioners.
– Tensioning ensures that the wire’s tension is virtually independent of temperature.
– Auto-tensioning or constant tension is used for medium and high speeds.
– Tensioning the line makes waves travel faster and reduces sag caused by gravity.
– Tensions range between 9 and 20kN (2,000 and 4,500lbf) per wire.
– Fixed termination (FT) equipment can be used for low speeds and in tunnels.
– Tension is generally about 10kN (2,200lbf) for FT equipment.
– Continuous length of overhead line is limited with AT equipment.
– Midpoint anchor (MPA) restricts movement of the messenger/catenary wire.
– Brake mechanisms prevent wires from unraveling completely in case of wire break or tension loss.
– Braking mechanisms ensure the undamaged part of the wire remains intact until repair.
Section Breaks, Neutral Sections, and Dead Sections
– Lines are divided into sections to limit outages and allow maintenance.
– Sections often correspond with tension lengths.
– Transition from section to section is known as a section break.
– Different methods are used for bow collectors/pantographs and trolley poles.
– Pantograph-equipped locomotives must not run through a de-energized section break.
– Neutral sections are placed between sections fed from different power grids or phases.
– Neutral sections prevent backdoor connection between unsynchronized grids.
– Permanent magnets and transducers are used to open/close electrical circuit-breakers.
– Lineside signs warn drivers to shut off power and coast through the neutral section.
– Midpoint of the neutral section is often earthed for increased safety.
– Dead sections are isolated portions of the overhead line.
– Used for maintenance purposes.
– Phase breaks are indicated by specific signals or signs.
– Metal signs with drilled holes indicate phase breaks on some railroads.
– Dead sections ensure safety by preventing power flow and maintaining isolation. Source: https://en.wikipedia.org/wiki/Catenary_(railways)
An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, trolleybuses or trams. The generic term used by the International Union of Railways for the technology is overhead line. It is known variously as overhead catenary, overhead contact line (OCL), overhead contact system (OCS), overhead equipment (OHE), overhead line equipment (OLE or OHLE), overhead lines (OHL), overhead wiring (OHW), traction wire, and trolley wire.
.jpg)
An overhead line consists of one or more wires (or rails, particularly in tunnels) situated over rail tracks, raised to a high electrical potential by connection to feeder stations at regular intervals. The feeder stations are usually fed from a high-voltage electrical grid.
