In 2015, Novo Rail – an alliance between Transport for New South Wales (TfNSW) (owner partner and client), Aurecon, Laing O’Rouke and RCR Infrastructure O'Donnell Griffin – was selected to deliver an AUD 1 billion infrastructure upgrade programme of the Sydney rail network over five years.
In the Sydney Trains network, timber high-voltage aerial poles have been used almost exclusively for the past 100 years. While their insulating properties are well known, timber poles have significant downsides. They are prone to rot, susceptible to termites, and have height limitations.
As part of a programme to modernise the Sydney suburban and intercity rail network, TfNSW was seeking to improve its power supply infrastructure. Stage 1 of this work included the Novo Rail Strathfield to Hornsby 2 kV-11 kV Feeder Upgrade, which had been designed using standard timber poles.
During the planning phase, however, the requirement for longer poles became acute due to changes in standards that had increased the required foundation depth. The transportation of the necessary 23-metre-long poles added significant complexity to the project. To address this, the project team considered alternative materials to construct longer poles and deliver the upgrading project.
Steel high voltage (HV) aerial poles have not previously been widely used on the suburban network due to the risks posed by stray traction current through a metal structure. However, steel could easily be sourced, manufactured, transported in sections, and constructed on site.
To facilitate the use of steel and insulate the current, Aurecon in its role as the designer within the Novo Rail alliance, proposed the innovative use of a rail safety device known as a ‘low voltage limiter’. The unit is installed on a steel HV aerial pole to separate the overhead earth wire from the pole. Effectively, this blocks stray traction current from silently and invisibly eroding the steel reinforcement inside the poles’ concrete foundations.
TfNSW and the operator (Sydney Trains) were eager to investigate and assess the opportunity to cease their use of timber HV aerial poles and replace them with a more durable material.
To ensure the low-voltage limiter met TfNSW and Sydney Trains specifications, Aurecon:
Trains are supplied at 1500 V DC from overhead wires, then the DC current returns to its supply via the train wheels and steel rail tracks. The rails are intended to be insulated from the general body of the earth, however, the insulation is not infallible. Some return current passes back to the traction substation via routes other than rails. This is referred to as ‘stray’ traction current.
Stray traction current can cause corrosion of steel foundations and pipes at any location where it exits steel structures into the earth.
The risk of stray traction current arises due to the way the Sydney Trains network, HV aerial lines at 33 kV or 66 kV tend to run in parallel with the railway lines. As such, the overhead earth wire of a HV aerial line is a potential route for stray traction current to return to the traction substation.
Aurecon’s challenges were:
A device meeting this objective is on the one hand supposed to be ‘blocking’ current (the DC traction current) and on the other hand ‘allowing’ current (the lightning surges and AC fault currents). Any such device must be extremely hardy, as it will be directly in the path of lightning strikes to the overhead earth wire.
Finally, the arrangement needed to offer cost and maintenance advantages to the operator Sydney Trains, at least sufficiently to make up for the disadvantages of timber.
The solution consisted of using an existing safety device in an innovative way. The product, ABB HVL 120-0.3, (a Hybrid Voltage Limiting device) was developed for personal protection from touch voltages, and protection of equipment from over-voltages. It is typically mounted at the base of a mast for the overhead contact lines in the railway.
In our solution for HV aerial poles, this technology has been adapted to block stray traction current rather than primarily act as a safety device.
The manufacturer was initially doubtful their device was suitable in this circumstance. However, they realised the enhanced capability once the project team had fully described the intention of the innovation, provided concept drawings, and discussed the specifications in detail.
Completed in 2017, the Novo Rail Strathfield to Hornsby 2 kV-11 kV Feeder Upgrade, Stage 1 HV aerial upgrade has now been constructed and commissioned into service.
The major benefits from this approach were:
For the rail network operator Sydney Trains, this innovation opens up the potential for steel poles to be used for any HV aerial feeder upgrades in their network, as well as for individual pole replacements as required. Sydney Trains has recognised the reduced ongoing maintenance compared to timber poles contributing to a safer, more efficient and more reliable rail network.