3M Cold Shrink Joints & Terminations - Network Rail PSU Project

3M Cold Shrink Joints & Terminations - Network Rail PSU Project

The Inside Track on Network Rail’s PSU Project

3M Cold Shrink Cable Joint

The Power Supply Upgrade (PSU) project carried out by Network Rail over the past three or four years has truly been on a grand scale.  It was the largest electrical supply project in Europe at the time and the biggest electrification project in Britain’s railways for well over fifty years, costing over 500 million pounds.  More importantly, it has been considered a resounding success.

Yet few people know the inside story on many of the engineering aspects of this feat of modern construction, and in particular, most will not be aware that much of the project was dependent on the massive cabling system carrying power between the grid and the sub-stations along the tracks.  The reality is that within any major power project, the cabling system acts as the bloodstream, with hundreds or even thousands of cables joints enabling the power to reach the right destination, safely and reliably.

3M Cold Shrink products have played a key role in the Network Rail PSU project, enabling the fast, consistent and safe installation of literally thousands of electrical cable joints and terminations.   In this way, 3M Cold Shrink helped Network Rail to overcome the timescale challenge and sheer volume of work that it faced.

The challenges of laying power cables

While laying cable and joints may sound straightforward, the reality is often somewhat different.  Timescales and working conditions can make installation extremely challenging, creating the potential for error or compromise, which can lead to cable joint failures that can cost a lot of money to put right.  It is testament to the quality of the work and equipment used by Network Rail, its partners, contractors and installers, that the project took place with very few problems and delays.

The story starts several years ago, when the UK government decided that all old-style slam door trains had to be replaced, largely due to health and safety reasons. At the time, over 1700 of these, known as Mark One Trains, were still in service on the South of England’s rail tracks.  These were to be replaced with over 2000 brand new trains, which as well as having automatic doors, also have features such as air-conditioning.

While good news for travellers, these trains also required approximately 23 per cent more power.  It was also agreed that the existing rail power system would require assessment to ensure sufficient power was provided to service the new trains, hence the PSU project came into being.

The logistics
Network Rail took the decision to divide the work into four main regions, with a different contractor responsible for each: Greater London (Seeboard, Balfour Beatty and WS Atkins), Wessex (Siemens and Amec), Kent (ABB and Mowlem) and Sussex (IUS and First Engineering).  From the outset, it was clear that the project would require a huge amount of co-ordination between the different elements of the project.  This was carried out centrally by Network Rail.

Logistically, the project was very complex, with Network Rail having to address issues such as ‘possession availability’ environmental impact, access to sites and making sure that the right components were not only selected, but provided in sufficient quantities ‘just in time’.  Work also had to be carried out pretty quickly, as the project timescales were tight from the outset.

Melvyn Paynton of Network Rail was a project engineer for the PSU project.  He says, “Network Rail had to schedule its purchasing carefully, so that we did not have products too early or too late.  From the engineering side, we also worked closely with our own product acceptance people, which helped to reduce the timescales involved.”

Examples of how this approach then reflected in eventual purchasing decisions include the use of single core cable (in this instance, XLPE  300mm square conductor cable), because the cable drums were more portable than three core cable and did not require special joint bays.  Of course, this meant that more cable had to be installed, with cable joints staggered along the tracks.

3M cable joints and terminations played a key role
A key decision was to adopt the ‘cold applied’ technique for joining and terminating cables, pioneered by 3M and increasingly prevalent in power networks across the world.  Indeed, more than half of the UK’s public power utilities use 3M Cold Shrink products today.  Within network rail, these joints were primarily used on the HV feeder cables, each typically three to five kilometres in length, providing power from the grid to sub-stations along the tracks.  Says Melvyn, “Due to the sheer volume of work involved, getting cable installed into the sub stations was one of our biggest challenges.”

The principle behind Cold Shrink is simple: rather than using heat and resins to join two cables together, a pre-stretched joint body is slipped over the cable two cable ends and shrunk to a watertight and EMI-resistant fit, simply by pulling a spiral cord from within the internal faraday cage.

Melvyn Paynton explains the thinking behind taking this route: “As I come from a cable jointing background, I could immediately see the benefits.  It allows a uniform, simple application, so there is less room for mistakes.  Of course, the installer still needs to prepare the cable properly before applying the joint, but it is far more consistent.  Another benefit is that as there is no heat being used, there is no need to carry LPG canisters up and down the track, as well as being better from a health and safety point of view.”

Although using the Cold Shrink joints and terminations is pretty straightforward, Network Rail wanted to make sure that all installers felt comfortable with the process, so it worked with 3M to provide training.  Reception by installers has been excellent: “There have been thousands of Cold Shrink joints and terminations used on the PSU project and we have had an extremely low failure rate.  I haven’t heard an installer say a bad thing about 3M.”

3M Cold Shrink enabled faster installation
Darren Howes was one of the installers on the project and echoes Melvyn’s views: “Cold Shrink is a lot easier to use and we can do joints and terminations a lot quicker. Although cable preparation is the same, overall completing a joint takes about half the time.  Not having to carry gas bottles means that I could do a joint by myself, and more quickly, it was a lot less back-breaking, as I wasn’t bending over for so long. We also didn’t need to worry about having to apply for hot works permits.”

Through close co-operation between the contractors, approximately 6km of cable was installed per shift using a cable train, often involving undertrack crossings.  In the region of 300 kilometres of cable was laid in total, requiring thousands of joints along the way.  Apart from adding extra sub-stations a significant number of substations were upgraded.  Three new connection points to the national grid were installed and a further five were upgraded.  17 brand new HV feeder cables were also put in place and 46 feeder routes upgraded.

3M PADS approval
Following their success in first part of the PSU project, 3M Cold Shrink joints are now being used for a second project to update three-core connections 33kV in sub-stations and switchgear, to overcome the complexity of creating trifurcate joints.  Furthermore, 3M is currently the only supplier to Network Rail with Parts And Design System (PADS)-approved joints and terminations across 11, 22, 33 and 52kV voltage classes.

The project was completed to schedule in 2006.  As well as ensuring that travellers in the South of England are benefiting from safer, more comfortable trains, PSU has also re-confirmed Network Rail’s status as the largest and one of the most advanced power utilities in the UK today.

PSU Key Statistics

  • 300km new cable
  • 3 new national grid supply points, 5 upgraded
  • a significant number of new sub-stations
  • 2025 new trains
  • 23% more power needed
  • 17 brand new feeders
  • 46 upgrade feeder routes

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3M Cold Shrink High Voltage Cable Joints and Cable Terminations, Network Rail PADS Approved

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