01.01.12
Listen closely
Source: Rail Technology Magazine Dec/Jan 2012
The trial of trackside ‘listening’ technology has proved such a success for South West Trains that it is now being expanded to cover the whole fleet, as engineering director Christian Roth tells RTM.
Axle bearing failures can be costly and hugely disruptive to passenger services, and traditional ways of monitoring bearing condition have not always been particularly effective.
But acoustic ‘listening’ technology, that compares how each bearing sounds with how it should sound, can provide an excellent early warning system. The technology uses an array of sensitive trackside microphones that listen to each axle bearing on every train that passes.
South West Trains has had the best-known version of this technology, Siemens Mobility’s RailBAM (Bearing Acoustic Monitor), in operation at Swaythling outside Southampton since late 2009, and in November 2011 it went live with a second system at Mortlake, near Richmond. The locations are vital, as between them, 100% of the South West Trains fleet is now covered. Each train is fitted with a unique tag that can be read by the acoustic monitoring system.
This is only the second such permanent application of the technology in Europe, as Christian Roth, engineering director at South West Trains, told RTM: “Clearly, the reason we installed the second system is because the first was just such a success. It worked very well on trains going to Southampton through the countryside, and with the system we have been able to detect bearing problems much, much earlier than in the past.
“What happened in the past was that usually when a bearing failure occurred, instant action was required, or you had a train that needed to be escorted back to a depot. That is very, very disruptive for the train service and for passengers.
“Having this equipment to detect problems earlier has meant we can put the bearing exchange activities into the normal maintenance schedule, and can plan for that at least four weeks in advance. That’s meant we haven’t been running into any kind of problems with those kind of bearings.
“Every time a unit goes past that system, the system is picking up if there are bearing problems. It can detect a unit number – every unit in the South West Trains fleet is equipped with a tag, and the system has a tag reader, so therefore can identify which unit is going over that system. We can then start to build a picture for each bearing about the condition it is in: ‘green’, meaning no problems, or ‘amber’, for example.
“We usually start the intervention once we have a significant number of passes over this system at an amber level – occasionally up to 20 passes. Then we start planning the maintenance. So it’s not about a single pass and warning lights flashing; it’s about plotting a trend for each bearing and deciding what the best time is to intervene from a maintenance point of view as well as from a cost point of view.”
Covering 100% of the fleet was key, he explained, and the Wimbledon-based 455 and 458 fleets obviously never go past the Swaythling device.
Theoretically the system can be used for any type of rolling stock, and it is already helping to monitor fleets owned by other operators whose trains pass the sensors.
Roth explained: “It will give a signal for any train going past the system, but what is needed is the tag on the unit, and for each different type of rolling stock, you have to identify and set the ‘alarm’ levels as well. For example, with the one at Swaythling, if there are significant alarm levels on freight trains or CrossCountry trains, then usually the information is passed to Network Rail for them to investigate. But, because we don’t have the tags, we cannot identify the specific units involved.”
Asked to quantify the amount of passenger disruption that the technology will help to prevent, Roth said: “In the past, before starting with this type of technology, we probably had about five failures per year, which totalled thousands of delay minutes. With this system, we probably bring that down to one per year because of bearing failures, so it is a substantial improvement.
“The number of delay minutes very much depends on the area the train failure occurs; the closer it is to London, the more disruptive it is to the railway, because of the intensity of the service, and therefore the new Mortlake system is quite crucial to avoid problems in that London area.
“From a whole industry point of view, Network Rail and South West Trains do see a cost benefit to putting it in to save delay minutes and improve PPM.”
Other operators are interested in the technology, Roth confirmed, although he said he couldn’t comment on the business case for them.
But he said: “It very much depends on the bearing condition, on the frequency of service, and the potential for it to be disruptive to their services. It’s clear that other operators, and even Network Rail in CP5 or CP6, are looking into similar types of technology for more widespread use across the network.”