Implementing cost-effective electrification

In 2009, the Great Western Electrification Programme (GWEP) was estimated to cost £1 billion. By 2015 the cost had risen to £2.8 billion. As a result, the programme was cut-back in 2017 with no electrification to Oxford, Bristol, or Swansea. This also led to a negative government perception of rail electrification and that bi-mode traction was seen to be the way forward.

Network Rail CEO Andrew Haines’ response was that “we must not underestimate the harm done by the horrendous costs and schedule over-runs on the Great Western electrification. The ball is firmly back in our court to show that we can deliver cost-effectively, and that we can be trusted.”

In 2019, the Railway Industry Association (RIA) published its Electrification Cost Challenge report which described how many aspects of the design and delivery of GWEP had added costs. As an example, instead of using long-establish empirical design guidance, GWEP’s designers had taken a risk averse approach and designed the piles from first principles which resulted in much longer piles than expected.

Once this issue was recognised, Network Rail commissioned a research project undertaken by the University of Southampton which demonstrated the suitability of the empirical method. This research was the basis for Network Rail standard NR/L2/CIV/074 ‘Design and Installation of Overhead Line Foundations’ which became a mandatory requirement in March 2018.

Reducing electrification costs

Work to reduce electrification costs has been done as part of an ‘enabling efficient electrification workstream programme’ which was jointly convened between DfT and Network Rail in 2021. To understand how this work has progressed, Rail Engineer was glad to have the opportunity to meet Richard Stainton, Network Rail’s engineering expert (electrification) who explained that the cost for an electrification project can be broken down into three parts:

• Route clearance – reconstructing bridges etc., or track lowering, to make space for energised overhead line equipment (OLE) and train pantographs.
• OLE installation – labour plant and materials. (Materials make up between 3-5% of an electrification projects cost).
• Other – Track access compensation, distribution, grid connections, signalling immunisation, de-vegetation, lineside fencing etc.

Richard considered that the biggest opportunity to reduce the cost of electrifying a route is reducing the volume of route clearance works. Therefore, a considerable amount of work has been done to provide evidence that the physical space required for electrical clearances can safely be reduced.

Although clearance was the main focus, the efficient electrification workstream programme has considered many other issues in an incremental approach that offered marginal gains over a wide range of issues was needed. To illustrate this, Richard produced a mind map that had eight categories with a total of 37 initiatives.

Although most of these related to electrical clearances others included:

• Bridge parapets – securing widespread adoption of deriving parapet heights from risk assessment rather than a blanket application of 1.8 metres usings the risk assessment methodology specified in the NR/L2/ELP/27717 ‘Bridge Parapet Electrical Risk Assessment’ issued in March 2023.
• OLE structure spacing – Following research on OLE wind loading by the University of Birmingham, NR standards have been changed to increase spacing between OLE structures from 65 metres to 95 metres to reduce the number of structures by an estimated 5%. This also offers designers greater flexibility to fit OLE structures around existing railway features.
• Rationalising traction distribution principles to reduce the number and complexity of electrical substations with designs that use the best modern practice in electrical power switchgear and control architecture. For example, modern protection systems enable track sectioning cabins to be replaced by disconnectors which give savings of around £2 million per 20km.
• Pantographs with inerters (a damper that resists force in proportion to acceleration) to improve the pantograph’s dynamic performance. This offers benefits that include reduced arcing and steeper wire gradients.
• Insulated pantograph horns – at stations the pantograph horn is the item of energised equipment that is closest to passengers. Also, at arched bridges it is the closest energised equipment to the bridge. Insulated pantograph horns, if fitted to all trains, offer benefits that include avoiding the need to cut back station canopies and reducing the number of bridge interventions.
• Reduced earthing and bonding – standard NR/L2/ELP/21085 previously required all conducting items that are located within 5.2 metres either side of track centre line to be bonded to traction return. This has been amended to everything within 30 degrees below the contact wire. As a result, the previous 5.2 metres distance has now been reduced to typically 3 metres to 4 metres from the track centre line.
• Protective signalling gantry mesh – the requirement in Euronorms to use a small mesh size can result in significant wind resistance. Hence electrification may require rebuilding of the signalling structure. The standard will allow for a larger mesh size which still provides full protection without the significant increase in wind loading.
• Ice – clearances used to allow for wire sag due to ice on the conductor were determined on the basis of the Electricity Commissioners’ Overhead Line Regulations from 1896. Using modelling techniques developed by the American Military, Network Rail has shown that the effects of ice on UK master series OLE falling below the minimum clearances is negligible. As a result, the environmental conditions that OLE designers are required to consider no longer includes sag due to ice. However, ice is still considered in respect of structural loading.

Under bridge clearances

Of all the cost saving measures considered, perhaps the one that has provided the most benefit is Voltage Controlled Clearances (VCC). VCC uses surge arresters and an insulating coating to reduce clearances under bridges to less than 63mm. With an allowance for a 43mm uplift, it was necessary to prove that it was safe to have a 25,000V bridge arm a mere 40mm below the bridge structure.

This clearance is normally governed by the need for the OLE to safely withstand voltage surges from arcing, switching harmonics, and lightning strikes which can exceed 100kV. Metal oxide surge arresters placed either side of a bridge ensure that the OLE under the bridge will not be subject to such surges and so needs only be designed for the maximum system voltage of 29kV. Under normal operation, surge arresters are open-circuit but have a low impedance during surges which then diverts the voltage surge through the surge arrester to earth.

The use of surge arrestors was first trialled on a high voltage test rig at the University of Southampton as described in Rail Engineer 190 (May-June 2021). They were subsequently fitted at Cardiff Intersection bridge to permit the route under the bridge to be energised in December 2019. This is a rail-over-rail bridge which would have otherwise required significant rebuilding costs. However, at such low clearance bridges it is essential that the track remains fixed in position. This is considered to be adequately managed by existing track management standards.

At this Cardiff bridge, the use of VCC saved an estimated £20 million pounds. Initial studies for future electrification schemes using the clearance methodology developed for Cardiff Intersection bridge indicates a reduction of more than 40% in the number of bridges requiring re-construction. This indicates that this VCC methodology has the potential to save hundreds of millions of pounds if there was to be a significant electrification programme.

To optimise this concept and further demonstrate its robustness, tests were undertaken in a high-voltage test laboratory in Budapest which was the only test house willing to build a ‘bridge’ in a high voltage test laboratory. This allowed the observation of 12,000 A fault currents for 300 milliseconds which is a far greater energy level than can be expected for typical short circuits.

NR/L2/ELP/27716

Many of the initiatives to reduce the cost of electrification concern electrification clearances, as specified in the 276-page Network Rail standard NR/L2/ELP/27716 ‘Electrical and mechanical clearances on overhead electrified railways’. This is essentially a manual and was issued in December 2023. It delivers the requirements of 13 different railway and British Standards as well as taking account of findings from the enabling efficient electrification workstream.

Its requirements are coded Red (no variations permitted), Amber (variations allowed subject to an approved risk assessment), and Green (use unless alternative solutions followed).

The first 22 pages introduces the four modules of this manual and refers to 92 reference documents.

The first module is a 97-page design specification for clearances. This considers the clearance between the three aspects of the OLE system which are: 1) OLE conductors; 2) OLE supports; and 3) Along Track Feeders (ATF) and twelve specific areas that might be impacted by the OCLS. These are:

• Overline structures (e.g. bridges, tunnels).
• Rail vehicle bodies.
• Pantographs.
• Signals.
• Single phase HV cables.
• Standing surfaces (non-restricted public access).
• Standing surfaces (restricted lawful public access).
• Standing surfaces (restricted non-public access).
• Level crossings.
• Vegetation.
• Third party land.
• Third party networks.

As a result, this first module defines the requirement for 22 types of static and dynamic electrical clearances as well as the requirements for the mechanical clearance between pantographs and overline structures.

As described later, a further module is a generic safety case for OCLS clearances. The third 50-page module provides the design input parameters and secondary calculations that are required for such matters as track fixity, rail vehicle kinematic reference profiles, pantograph sway, contact wire uplift, and wind speeds. The fourth and final 11-page module has tables which categorise the electrical insulation performance of clearances in 25 kV electrification systems.

Authorising new electrification

The Railways (Interoperability) Regulations 2011 require that no new subsystem (e.g. new electrification works) can be put into use on the UK rail system unless the Office of Road and Rail (ORR) has authorised its use. This requires a demonstration that the subsystem is technically compatible with the rail system and that it has been designed, constructed, and installed to meet the subsystem’s essential requirements.

The authorisation process requires the applicant to submit a formal safety assessment report which includes a common safety method risk assessment and certificates of verification by an independent notified body.

It would be reasonable to consider that new electrification work designed and installed in accordance with Network Rail standards is compatible with the rail system. Yet, the approval process requires that this be demonstrated from first principles.

As an aid to project teams, the second module of NR/L2/ELP/27716 has a generic safety case for OCLS clearances. This includes a system definition, lists of hazards, and methods that might be used to demonstrate the effectiveness of control measures such as surge arresters. It also provides bow tie diagrams (these show an accidental event in terms of its initial causes, negative consequences, and the barriers intended to prevent or control its associated hazards), a spreadsheet recording 55 hazards, and shows the OCLS and AFT design hierarchy.

Thus, this module of NR/L2/ELP/27716 provides a generic safety case that can then be cut and pasted into the safety assessment report to which a relatively small number of project specific issues are added. Hence the safety approval process for electrification projects, in effect, requires each project to demonstrate that Network Rail’s electrification standards are fit for purpose. It is not clear what purpose this serves.

Retaining expertise

The work of the efficient electrification workstream has done much to address Andrew Haines’s warning that after GWEP, the industry has to be trusted to deliver electrification efficiently. Since then, much work has been done to provide the evidence that standards are fit for purpose and incorporate the findings of research done to reduce the cost of electrification.

As a result, GWEP’s design and construction issues have now been addressed. Yet there may well be scope to reduce off-site costs by, for example, reducing overheads and an improved contracting strategy. It is also clear that safety approval costs could be reduced.
The 276 pages of NR/L2/ELP/27716 are a reflection of the complexity of electrification engineering and highlight the need for electrification work, such as much needed freight infills, to retain expertise in electrification design and construction. Without such projects expertise will be lost, so when electrification work resumes, as surely it must, new mistakes will be made, old mistakes will be re-made, and costs will be high.

It should be self-evident that the most reliable way to minimise electrification costs is a stable, long-term electrification programme that builds-on and retains the skills and experience necessary to deliver it effectively.

The GWEP electrification programme illustrates this point. It started after there had been no new electrification for 20 years. When it became apparent that some of its OLE mast piles were designed to be three times longer than those used on previous schemes, it should have been apparent that this was a hugely expensive mistake. Yet there was no-one in authority with electrification experience who could halt the use of such piles.

This is a lesson that should not be forgotten.