3M - Why Electrification Is So Essential To The Performance Of Our Rail Networks

3M - Why Electrification Is So Essential To The Performance Of Our Rail Networks

At the heart of any rail network are massive electrical cabling systems that carry the power between the substations and power distribution along the track. The cabling system acts as the ‘bloodstream’, with hundreds - or even thousands - of low / high voltage terminations and joints enabling the power to reach the right destination, safely and reliably. Apart from increasing traffic, more legislation and growing competition, the advent of more sophisticated rolling stock and a demand for higher travelling speeds all place considerable pressure on the electrification systems on which the rail networks depend. Therefore the role of electrical distribution, and so the very cable terminations and joints within rail networks, is more important than ever before.

While laying cables and then terminating and jointing 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, and this can lead to termination or joint failures that can cost a lot of money to put right. Timely and accurate LV/HV cable terminating and jointing can be ‘make or break’ for a rail installation project’s success. So what can be done to make installation more reliable and straightforward?

One approach is to use a ‘cold applied’ technique for the terminating and jointing of cables. Pioneered by 3M, this approach is 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. The principle behind 3M Cold Shrink is simple: rather than using heat and resins to join two cables together, a pre-stretched stress control and outer protection body inclusive of any necessary mastic is slipped over the cable end (or ends) and allowed to shrink giving a watertight and electromagnetic interference (EMI)-resistant fit, simply by pulling a spiral cord from within the internal Faraday cage.

The benefits of using products like 3M Cold Shrink include reduced room for manual error, so cable joints and terminations can be installed to a consistent and high standard. Furthermore, since the joint or termination body is installed as an all-in-one unit that has been pre-stretched, installation time is reduced. This was certainly the experience of Network Rail and its installers, when they used 3M Cold Shrink as part of the PSU (Power Supply Upgrade) project, the biggest electrification project in Britain’s railways for fifty years.
Network Rail’s PSU project
Melvyn Paynton, project engineer for the PSU project, says “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. Another benefit is that there is no heat being used, so there is no need to carry LPG canisters up and down the track.”

Darren Howes was one of the installers on the project and echoes Melvyn’s views: “3M 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, doing a joint takes about half the time.”

Melvyn Paynton adds, “There have been thousands of 3M 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.”

Electrification and new high-speed networks
Of course, no market stands still and new trends in rail infrastructure place new pressures on electrification. One of the biggest shifts is a move towards dual 25kV electrification, which is fast becoming the de facto choice for long-haul railways across Europe, including the UK. Network Rail’s Mike Coupe says, “25kV electrification is the world norm, and that is now shifting to dual 25kV. It is the way of the future.”

Dual 25kV literally doubles the power available to rail networks and hence, is helping rail operators to meet some of the demands they are facing, such as the need for faster travel, the ability to support more sophisticated rolling stock and travel over greater distances.

Dual 25kV is expected to play a key role in the vision of high speed rail networks that will enable customers to stay on the same train across long journeys, even across multiple countries. Having a standard electrification system across different networks will provide economic and operational benefits, such as avoiding having to
convert power supplies and voltages during the handover between different rail operators.

In recent years, two projects – the West Coast Main Line (WCML) upgrade and the CTRL (Channel Tunnel Rail Link, the first new UK railway for over 100 years, now known as High Speed 1) – have deployed dual 25kV power systems. Both these projects have used 3M Cold Shrink jointing and terminating, which is able to support dual 25kV cable systems. 3M is the first cable accessory manufacturer to have approval for a 52kV class cable termination, meaning that 3M is now able to offer Network Rail-approved joints across 11, 22, 33 and 52kV voltage classes. 72kV, now fully released by 3M, is hoping to also be used.

Addressing individual network challenges
Of course, every rail project is going to have its own very specific challenges and this was the case with both High Speed 1 and WCML. Says John Hughes, an Electrical Engineer with Birse Process Engineering Ltd, part of the Balfour Beatty group of companies, which was the main contractor on the High Speed 1 project:
“Taking 25kV and 11kV supplies through tunnels to meet strict 21st century safety regulations meant specifying joints and terminations which no supplier stocked as a standard product. Fortunately, 3M met the challenge with modifications to its 3M Cold Shrink joints and terminations and by incorporating other products from the 3M arsenal of innovative technology. To meet the specialised earthing requirements, the earth connections were taken outside the joint and cross-bonded. To comply with the LSOH standard (Low Smoke, Zero Halogen) – mandatory in tunnel sections – 3M incorporated its specialised 69 Fire Tape into the product spec.”

The WCML upgrade has presented Network Rail with other cable installation challenges. Using the dual 25kV autotransformer feeding system has many benefits, but it also has its problems, particularly when it comes to taking power through tunnels and under bridges, where clearance between power conductors is limited. The autotransformer system adds another conductor, so to overcome this, Network Rail and its joint venture partner developed a strategy whereby the 25kV feeders can be interconnected through the top of the tunnel or bridge using insulated feeders, with the 3M cable terminations placed horizontally at either end. It is the ability of
being able to use the termination in the horizontal that was significant as no other technology allows this. Says Network Rail’s Mike Coupe, “Using 3M Cold Shrink saves us space and gives us additional functionality. It allows us to seal the cable in the horizontal plane and is far easier to accommodate.”

Alan Telfer of Atkins adds, “The cable preparation is the same, but once that is done, installing the 3M termination takes just minutes using 3M Cold Shrink. There is no need to use heat torches or to set up tents – if it is raining, we can just hold up umbrellas. There is also reduced room for error and installation quality is more consistent.”

Clearly, paying close attention to cable jointing and terminating at the early stages of any rail upgrade project is essential to its overall success. While cables may not grab the limelight compared to other, more seemingly glamorous aspects of rail installation, their accurate installation is vital to the smooth-running of our rail systems. With its ever-evolving range of Cold Shrink solutions, 3M is committed to supporting its rail customers now and in the future.

Network Rail Approved 3M Power Cable Joints and Terminations


3M Electrical Products Catalogue

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