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Safer isolations

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In 1883, Magnus Volk heralded the dawn of a new era in Great Britain with the opening of Volk’s Electric Railway, which, 135 years later, is still transporting pleasure seekers along Brighton promenade and is the world’s oldest operating electric railway.

Since then, the use of electricity to power our trains has been ever expanding – initially on London Underground, then with some suburban lines prior to the First World War.

Further electrification followed during the interwar years, with large investment by the Southern Railway. This included the world’s first electrified intercity route between Bournemouth and London.

In the years following the Second World War, rail electrification in and around London and the South East was further expanded. The 750V DC third-rail system south of the river Thames continued expanding until 1988, and now extends from London to as far as Folkestone in the east and Weymouth in the west.

Since privatisation, traffic on this part of the network has doubled, and some of the original equipment and infrastructure is still in use. Most new UK electrification since the 1960s has been 25kV AC overhead line, but, given the scale of the electrification in the south east, the massive capital cost of any conversion means that 750V DC with ground-level conductor rail is here to stay for the foreseeable future.

With the increase in passenger numbers, and the age of the infrastructure, one of the biggest challenges in rail operation is the time available to carry out essential maintenance. On the DC routes, this is often even more crucial because of the higher traffic load and wear – all in all, more work to do and less time to do it.

Unlike an overhead system, the conductor rail must almost always be isolated to allow even simple tasks (like replacing a sleeper by hand), which, of course, requires more planning and coordination as well as the services of a strapping team to make sure the power is off and to help prevent inadvertent re-energisation of the associated DC conductor rails. All of which leaves even less time to replace that sleeper!

Strapping for safety

So, what does the strapping team do? Once the block is granted, all the sections of conductor rail in the possession are isolated by either the electrical control room or by staffing of the relevant substations. Members of the strapping team then go to the extremities of the block and to key points in between, check by testing to be sure the conductor rail is off, and fit short-circuiting straps between the conductor rail and the running rails before signing off the relevant forms. Only then can works begin.

In the event of the conductor rail accidentally being re-energised, the straps that were fitted by the strapping team will create a direct short circuit to the negative return path of the DC system, thereby causing the DC circuit-breakers associated with the isolation to trip immediately, protecting the personnel at the worksite.

The strapping team has a key safety role, but its job also carries considerable danger. Not all the tracks near the worksite will be blocked or isolated, so not only is there a significant risk of being struck by a train, but the straps might accidentally be put on a live conductor rail. And there’s also the issue of finding their way in the dark to exactly the right place, in all weather conditions, in both remote country and some fairly hostile urban areas, all while carrying testing equipment, straps, bar, gloves, brush, first aid kit and goggles, without delaying those who are keen to get working as soon as possible.

Over the years, the processes have been developed and honed, and it usually runs fairly well, however, it’s far from risk-free. Something better, quicker and safer is needed.

Improved methods

This traditional way of strapping is termed a B2 isolation. The safety guide for strap application has six steps – see box. It all takes time and puts workers at risk.

Network Rail was under two pressures to make improvements. Its own desire to reduce “boots on the ballast” and keep its workforce in a position of safety at all times was combined with a need to comply, in all respects, with the Electricity At Work Regulations.

Bring in B4

As a first step to automating the process, Network Rail developed the B4 isolation. This uses a negative short-circuiting device (NSCD) to bond the conductor rails and keep people working on track safe. However, the difference is that, unlike the SCS that has to be connected manually on the track, the NSCD works at the substation by flicking a switch.

In March 2014, Network Rail awarded an electrification and plant framework contract to McNicholas (since July 2017, part of Kier Group, a leading infrastructure, buildings, developments and housing group), as well as a similar one for Kent and Sussex. Wessex was subsequently chosen as the pilot area for the ‘Safer Isolations’ programme, with the work to be performed under the framework contract, by McNicholas (now Kier) as the leading contractor due to its extensive experience in delivering power, telecoms and signalling contracts across the rail network.

Antagrade Electrical, with its long history of design, installation, testing and commissioning on rail power systems and key Level A resources, was asked by Kier to come up with a detailed electrical design for the new NSCD equipment for B4 isolations. This involved attaching a control panel to each substation, together with fitting the short-circuit equipment.

Once the design was proven, the next phase was to improve the speed with which an isolation could be taken still further. Many of the substations were not situated near access points. This meant that, although the isolation process could be undertaken by one individual rather than a team as before, they still had to walk alongside the active railway, often in the dark and maybe for several hundred metres, to reach the local control panel.

For this reason, three months after Kier received its contract from Network Rail and enlisted the help of Antagrade on the project, Sella Controls was asked for a communications solution to bring the control panel to the access point.

The proposal was to use equipment from Sella Controls’ Tracklink® product range. Andrew Yard, Sella Controls’ engineering lead for the project, explained that this involved using the company’s proven point-to-point (P2P) equipment to provide a working solution. This allows the control panel to be mounted remotely from the substation, connected to it by copper cables running through the troughing alongside the track. The remote panel can therefore be housed at the side of an access point, or a car park, to allow simple and easy operation without having to enter railway property.

James Bentley, Antagrade’s project manager, explained that, by providing each of the key DC circuit breakers, or in some cases the entire DC switchboard, with its own negative short-circuiting switch, and installing a control panel in an accessible location (usually by the roadside), the strapping team only needs to drive to the relevant panel(s) and request the control room to open the breakers.

Once the power has been disconnected from the relevant section, the local personnel can operate the control panel switches to apply the negative connection via the short-circuiting devices. This then ‘interlocks’, or disables, the operation of the DC Circuit breakers, preventing them from being closed once the NSCDs have been operated. The correct operation of the shorting devices and absence (or presence) of traction voltages are all indicated to the local operator at the control panel.

B4 becomes B5

The introduction of B4 isolations was a great success, both on Wessex, where Kier was installing them, and also in Sussex, where Siemens was doing similar work. However, it was on Wessex where the programme was taken to the next stage.

A B5 isolation was developed by Kier and Antagrade, bringing a number of short-circuit devices under the control of a single panel that would allow a longer section of the railway to be isolated at once, significantly improving access time. The solution utilises the combination of Sella Controls’ Tracklink RTU, acting as a consolidated control panel (CCP), and multiple Tracklink P2P units to provide the remote operation of NSCD equipment across a number of substation locations. Each CCP has the capability to control up to five individual local panels.

There are currently four sections under trial. One application is installed on a section between Staines and Datchet (covering three sites), with the remaining three sections between Guilford and Havant (covering twenty sites).

This test route, as well as being a busy railway, is well chosen for other reasons. The substation at Wraysbury, near Windsor Great Park, can only be reached down the railway tracks. Similarly, Datchet substation lies alongside the local golf club, again preventing easy access. A remote control solution is therefore essential, and one that can isolate long lengths of track is a bonus.

The B5 programme in Wessex is an operational trial, with the results to be assessed before a national roll-out. It is not a traction SCADA (supervisory control and data acquisition) isolation, rather each CCP forms its own discrete network with its associated local panels. B5 is a SIL 0 system (safety integrity level 0 – not technically part of the standard, which starts at SIL 1, but commonly used to classify safety systems that are not required to meet a safety integrity level standard), allowing one person to short, isolate and reinstate. This contrasts with the similar ‘emergency traction discharge’ system on London Underground, which allows a train driver to kill the power in the event of an emergency but needs clearance from a second person before power can be reinstated and is a SIL 2 system.

So B5 isolations will make access in the short night-time windows quicker and lengthen the time available for productive work. However, paradoxically, the B4 and B5 equipment, substations and NSCDs, had to be installed without that benefit as it wasn’t yet in place!

“Installation of the NSCDs is not, in itself, complicated,” commented Sam Eversfield, Kier’s assistant project manager, “but installing them in a rail setting adds pressure. The work has to be carried out on a Saturday night, within tight time constraints, to allow for the train companies to reopen lines.

“The challenge has been in accessing the sites, which are often in the middle of the countryside such as a farmer’s field.” With rail-mounted Kirow cranes being used to lift equipment into position, it all has to work like clockwork.

Ongoing success

Network Rail is very pleased with the way the introduction of NSCDs is progressing, both on the Bournemouth and Brighton main lines. Project engineer Peter Roberts, based at Waterloo, reported: “There have been a number of instances where a strapping team has incorrectly installed the straps, not tested before touch, installed the straps at the wrong location on a line, or even on a wrong line, and most importantly, have sometimes suffered serious injury as a result of errors or omissions. And that, of course, is after reaching the strapping point itself, having sometimes walked great distances.

“When operating the NSCDs, there is no risk of providing a negative short circuit in the wrong location, or incorrectly. The time taken for a number of sections to be shorted out reduces dramatically.

“As an example, there is a trial installation at Ludgate Cellars, where there are fourteen NSCD units. The strap men there has advised that, as a single team, they would require two hours to strap the same fourteen sections using traditional methods. When timed using the NSCDs, they took seven minutes, and that was the first time they used them in anger. They also did so from just within the Substation compound.”

Kier, Sella Controls and Antagrade are currently working on 26 B4 sites for Phase 1 and another 36 for Phase 2 of the programme. Phase 1 is due to be completed by the end of March 2019 and will include 198 NSCD units while Phase 2 involves installing 237 of them. Work has so far covered lines from Waterloo going out through Surrey to Hampshire and the first isolation has already gone into service.

After all of this hard work, it’s quite possible that B4 and B5 isolations won’t actually last very long. The ultimate goal is to control all of the NSCDs from the central traction-power control desks at the rail operating centres (ROCs), although no doubt the facility for local operation will still exist if needed.

Safer Isolations isn’t just a DC project either. Already work is being carried out in Scotland and on Merseyside to see how the lessons learned can be applied to AC traction power as well, but that’s another story…

Read more: The past, present and future: A look at electrification of the UK’s railways



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