The phrase “signal failure” is enough to strike fear into the heart of any travel-weary commuter on the London Underground network. It’s a familiar precursor to stationary trains, delays and soaring levels of passenger frustration. This is particularly true on the Victoria line, where a service runs every two minutes.
Over the past eight years, a £1 billion investment on the Victoria line has improved its reliability. The upgrade includes the introduction of a new signalling system of 385 jointless track circuits to detect train position, maintain safe separation distances and deliver train headways capable of meeting the extremely demanding timetable. The track circuits are the sole means of train detection and play a critical role in the railway’s safe and reliable operation. However, no provision was made during their design for remote-condition monitoring of their performance. That meant it was necessary to manually monitor the condition of every track circuit, on-site, with a digital multi-meter, a costly, time-consuming task with little scope for predictive maintenance.
Eventually, a decision was taken to develop a more sophisticated large-scale distributed system that could simultaneously monitor track circuits in real time from a central location. The recently installed upgrade is delivering greater knowledge of track circuit conditions, allowing pre-emptive maintenance. Ultimately it should mean fewer track circuit failure and service delays.
Sam Etchell, the engineer responsible for the development of the remote-condition monitoring system, says that it has proved to be a necessary and valuable investment.
“The Victoria line carries 650,000 passengers a day – and there can be many thousands of people in transit at any one time. Track circuits are the most catastrophic type of ‘signal failures’. When they fail, they fail safe, so we suspend the service. There’s also a reputation issue at play. When you’ve invested £1 billion, there’s an expectation of a good service.
“The jointless track circuits that had been installed were causing problems for a variety of reasons. The maintenance regime was every six weeks, with staff going out on the track and checking every one of the 385 jointless track circuits. It was a huge task – and it was very manual. The checks weren’t really aimed at allowing us to predict failures – they were just part of the track’s overall maintenance regime.”
That led, about a year ago, to the formation of the Victoria Line Condition Monitoring Team, made up of six professional engineers with rail, software, electrical, mechanical and network-engineering backgrounds. The challenge was to design, integrate and install an intelligent remote-condition monitoring system that could perform real-time analysis of voltage and frequency for all jointless track circuits across the 45km length of the Victoria line. This would allow engineers to predict and prevent failures, and subsequently reduce delays on the line.
The Victoria line deploys variable length frequency-driven tuned electrical jointless track circuits that energise and de-energise as trains traverse the line. Each circuit includes an electrical receiver unit matched to the frequency of the track circuit (4-6kHz), which processes the incoming signal and provides a sample to a monitor point that can be used to check the track circuit’s health. The new system had to be able to simultaneously acquire the monitor point samples remotely from all track circuits on the line, sifting through the data to deliver meaningful information which would provide alerts to a central human machine interface (HMI).
Easy access: Touchscreen devices are able to log on to the monitoring system
The first step in the development of the system, says Etchell, was to assess off-the-shelf data acquisition products currently on the market. “We subsequently decided to go for the CompactRIO platform from National Instruments running LabVIEW software – because it met a variety of performance criteria,” he says. “These units would be expected to take samples from the track circuits 250 times a second. Taking one station – Seven Sisters – which has a total of 58 track circuits, that’s quite a lot of data.
“There had to be flexibility – we wanted the option of being able to add in sensors to measure other assets, such as points, in the future. The diverse range of input modules and the ability to easily customise the onboard software using the NI LabVIEW platform helped to reduce the time needed to design and develop the hardware and software for a wider range of data inputs.”
Due to the Safety Integrity Level of the track circuit system, an independent isolation barrier between the receiver unit on the track circuits and the CompactRIO device was required. A module to provide galvanic isolation between the data-acquisition device and the track circuits being monitored was built in. The module had to provide an accurate and compatible replica of the track circuit output signal for the CompactRIO acquisition.
A decision was made to split data acquisition across 14 separate sites that were all part of a new fibre optic network installed for the new system. The data would then need to be fed to a central condition monitoring server, next to Tottenham Hale station, in real time using a lightweight transfer protocol.
“This was a key requirement in the design and delivery of a true remote condition monitoring system,” he says. “The central condition monitoring server processes a live 10Hz data stream from every CompactRIO device, which totals more than 4,000 data samples per second. The lightweight data transfer protocol ensures that the central server can rapidly analyse the data and monitor track circuits for deviations from ideal condition.
“The system allows each track circuit to have its own standard frequency and voltage. Each section of track is different, so variable conditions are required. The central server has knowledge of what the ideal condition for every track circuit is, so it can make a decision on the health of each track circuit connected to the CompactRIO input channels. In addition, the server stores all the data in a near-line and far-line database for long-term trend analysis on large datasets.”
The central server then pushes asset condition alerts to an HMI. This is a large touchscreen device that displays an accurate scaled replica of the Victoria line track circuit configuration. A user can navigate the displayed information with natural touch gestures, identify line-side asset condition and receive predicted equipment failure warnings.
“We plan to deploy two more HMIs for faster response times – one in the maintenance control centre and one in the Network Operation Centre,” says Etchell. “Both can be used by signalling maintenance staff. We can remotely interrogate each track circuit on the railway with a single touch, presenting the user with a live graphical representation of the root mean square voltage, frequency and track state information using the data streamed from the line-side CompactRIO devices.
“Alongside the HMI, a suite of touchscreen devices can display the data in the line-side equipment rooms and through a smartphone or tablet. This means the data from the CompactRIO devices is available anywhere on the Victoria line via the new condition monitoring network.”
The monitoring system also allows retrospective interrogation of trends. This kind of data analysis allows informed decisions to be made on preventative maintenance.
The condition monitoring system was installed over three months and is now fully operational. Etchell says it has performed well, but that it has missed the occasional track circuit failure. “That’s to be expected,” he says. “But now we can go back and pull out the data and work out why it was missed. Then we can change our algorithms to make sure that we don’t miss it in future.”
He says the system has delivered Tube engineers with far more accurate knowledge of the real world behaviour of jointless track circuits.
“It helped us to better understand a critical asset, learn the behaviour of a faulty track circuit, identify those that could potentially fail and alert maintenance prior to this event occurring,” Etchell says. “The system is forecast to reduce lost customer hours by 39,000 per year – an estimated £350,000 savings per year in terms of passenger dis-benefit.”
Looking forward, there are plans to bring other assets on to the systems. “That will offer an integrated view on the Victoria line, and then others,” he adds.