Hengoed and Llanbradach - ingenious workaround preserves integrity of listed footbridges

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When two listed footbridges threatened to disrupt electrification of the Rhymney branch of the Core Valley Lines, Amey Consulting design team found an ingenious workaround

The upgrade and modernisation of the Core Valley Lines (CVL) is a key part of Amey’s contract with Transport for Wales to renew the Wales & Borders rail network. Electrification in readiness for a new fleet of hybrid light rail vehicles is at the heart of the CVL programme.

The preparatory works have required extensive improvements to the CVL’s ageing infrastructure. One of the most challenging issues is the presence of several of Victorian bridges too low to provide the necessary safety clearance for the live overhead cables. Lifting or replacing them would cost millions of pounds and cause long delays.

To avoid this, Amey proposed use of a solution known as a permanent earthed section (PES). The current would be removed from the wires passing under the bridge, with the train temporarily switching to battery power. This would require the installation of specialised overhead line equipment (OLE) to manage the switch, but would obviate the need to modify the height of the bridge.

This option was accepted as the ideal solution for most of the affected structures. Unfortunately, it did not work for two listed footbridges at Hengoed and Llanbradach on the Rhymney line.

Like many others, the Victorian latticework structures did not provide the necessary clearance for live overhead cables. However, a structural assessment ruled out the option of either lifting them or installing OLE for a PES solution. They were simply too fragile. In addition, Cadw wanted to protect and preserve the listed footbridges, and would therefore object to any modifications to the bridges, including the raising of the parapets to comply with safety standards.

Having brainstormed the problem at a design workshop, the Amey team came up with a new proposal – rather than attempt to solve all the issues arising from the presence of electricity, simply remove it from the equation. Make the area around each bridge wire-free, with no live cables or OLE. A beacon would prompt the train to drop its pantograph on approaching the catenary-free section, switching automatically to battery power. A second beacon would signal the train to raise it again on leaving.

This deceptively simple-sounding but actually highly technical solution was made possible by one of Amey Consulting’s most important assets – a bespoke design model specially developed to simulate train and traction power systems. This unique tool allowed the team to analyse the movement of trains on the line and the state of charge (SoC) of their batteries at any given point.

This was crucial, as the efficient operation of the trains depended on the availability of battery power when required. The catenary-free sections would be an obvious drain, and the model helped to establish that batteries could recharge effectively when regaining access to live OLE. A miscalculation could leave a train without charge in a ‘dead’ zone. In addition, excessive charging and discharging would shorten battery life, adding to maintenance costs.

The resulting design resolves these issues, minimising the impact on battery life. It is an ingenious workaround that preserves the integrity of the listed footbridges and the CVL’s Victorian heritage without compromising operational requirements – saving millions of pounds and man-hours in the process.

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