RAILWAYS and operators from around the world are continuing to transition their train maintenance strategy away from traditional reactive and interval replacement practices to those based on the condition monitoring of specific components. As a result, train maintenance programmes are becoming smarter and increasingly efficient as life-cycles are extended according to the actual health of the asset, rather than just time in service.

Technology is inevitably playing a major role in delivering this new approach, allowing engineers to easily identify exactly when a certain component is reaching the end of its service life. Among the latest contributors to this field of solutions is a battery-free wireless condition monitoring technology developed by Perpetuum, Britain, which coupled with powerful analytical software, is making rolling stock condition monitoring and asset failure easier to view, manage and predict.

ConfiguringHowever, Perpetuum's technology varies from more conventional solutions. In a first for the rail industry, it utilises an electromagnetic vibration harvesting micro-generator. This technology is based on converting mechanical energy produced by vibration into electrical energy and is able to deliver the power required to reliably transfer large amounts of autonomous data from wireless sensors.

Analytical software subsequently packages this information into comprehensive datasets which provide insights into the health of fleets' wheelsets, wheel bearings, gearboxes, and traction motors as well as track conditions, which is sent directly to asset managers' PCs, tablets and mobile phones.

Britain's Southeastern franchise, which operates commuter services in London and the southeast of England, recently completed deployment of Perpetuum's technology on its fleet of 112 three and four-car class 375 Electrostar EMUs, and is already seeing the benefits.

In the county of Kent alone, Perpetuum now monitors over 1.8 million data points per day, and since 2013 more than 400 million service-km from more than 5000 sensors have been monitored on over 600 vehicles. This level of data has helped to produce the statistical models that form the basis of operator's life-cycle management processes, which are helping asset managers to reduce costs, increase safety and plan more efficiently.

The bogie-mounted vibration and temperature sensors were installed for the purpose of monitoring the rolling stock and the project paid for itself by allowing targeted maintenance and extending the period between overhauls.

One example of a component where remote condition monitoring of performance has replaced interval replacement is wheelset bearings. Perpetuum's technology is now allowing engineers to reliably and safely identify on average one bearing per month that was deteriorating. In addition, and just as importantly, the system has not highlighted a single wheel that was not showing primary degradation.

Southeastern and rolling stock leasing company Angel Trains have since committed to trialling the system on the franchise's class 465 and 466 Networker EMUs as deployment on the Electrostars nears completion.

The sensors are also yielding information on the track condition by providing 11,000 snapshots a day on sections of the Southeastern network, which can provide insights on the rate of change at, for example, a set of points at Tonbridge. This means the system is providing a supplementary service to that offered by inspection trains. The inspection train might pass every two months and give a detailed survey of track condition. However, with Perpetuum's system passing many times a day, it can give an indication of the rate of deterioration so engineers can carry out repairs based on constantly updated information, which can help avoid temporary speed restrictions on certain track sections.

Installation of the system is also underway on over 170 wheelsets on the 10 two-car and six four-car Bombardier class 171 Turbostar DMUs operated by Southern on non-electrified lines south of London. In Australia, Metro Trains Melbourne (MTM), which is planning to move to a condition-monitored maintenance strategy with the aim of significantly extending maintenance overhauls, recently ordered a pilot of Perpetuum's services. MTM will use the system to more effectively monitor the bearings and wheels on its fleet of Alstom X'Trapolis EMUs, 74 of which are currently in service and with eight additional trains set to be delivered this year.

In addition, trials are underway in London with Perpetuum's standard vibration sensor node for traction motor condition monitoring on a fleet of metro trains with the goal of safely extending motor overhauls. In Sweden, the technology has been fitted onto passenger operator SJ's fleet of X2000 trains with the goal of adding at least 40% more kilometres to the lifespan of bearings.

Vibration Energy Harvesters (VEHs), which are fitted onboard the trains, are the key technology on which the system relies. The history of this equipment dates back to 2004. Perpetuum emerged as a technology spin-off from the University of Southampton after it engineered, produced and commercialised the world's first practical electromagnetic vibration harvesting micro-generator, which was able to deliver the power required to transmit large amounts of autonomous wireless sensor data reliably from remotely monitored assets.

The electromagnetic-energy harvesters work by converting mechanical energy (vibration) to electrical energy via an oscillating mass (magnet), which traverses across a coil creating a varying amount of magnetic flux, inducing a voltage according to Faraday's law. Perpetuum's breakthrough design provided enough power to open up more options for wireless communications and a choice of applications, including rolling stock maintenance.

One of the advantages of VEHs is the absence of a need for high-maintenance batteries or hard-wiring connections to deliver this information. In Perpetuum's system, the VEHs power wireless sensor nodes transmit vibration data for long-term failure prediction, and temperature data for short-term monitoring, back to the asset manager's desktop or mobile device.

For bearing, wheel and track monitoring, one sensor node is fitted to each wheel using a customised bracket that meets national vehicle certification requirements. Sensor nodes can also be fitted to gearboxes and traction motors in a similar fashion to create a fully-enabled "intelligent" bogie.

The powerful energy harvesters are contained in one half of the node, while the other half contains a three-axis accelerometer, temperature sensor, wireless communications, electronics and capacitors. Data concentrators are used to provide wireless communications to the ground and enable remote monitoring of the assets' location via GPS. A single data concentrator is suitable for use with up to five cars, while two data concentrators are required for longer trains.

The energy harvester powered sensor node developed by Perpetuum is designed to last 20 years. Perpetuum's system is available as a turnkey solution or it can utilise existing telecommunications backbones and front-end displays. The sensor nodes are designed so they are easy to retrofit and do not require any modifications to the wheelsets with the process taking less than 20 minutes to complete. Once installed, assimilation of this real-time data and trending information into a train operator's future planning, maintenance and buying decisions can begin immediately.

A comprehensive on-call technical support team is also available for failsafe monitoring along with data protection and recovery systems. Perpetuum can provide training and operational assistance, while it is possible for the system to trigger the deployment of email alerts which are sent directly to the train operator and are escalated up a pre-specified hierarchical chain if there is no response within a certain time.

Freight wagons

While deployments have so far focused on passenger fleets, Perpetuum's system is suitable for monitoring freight wagons. Most wagons have no onboard power source, so the use of VEHs delivers monitoring functions without the problems associated with batteries.

Perpetuum supplies high-power VEHs, which are suitable for monitoring both the wagon and its freight for temperature, pressure, leakage and security. GPRS or satellite transmissions are available to send this data over long distances. Alternatively, wireless networks that communicate all data, including from wheelsets and freight, can use the power to send this information directly to the locomotive cab. GPS tracking is also a practical solution for monitoring the progress and position of wagons.

With the system also capable of analysing the wheel-rail interface, it is possible to quickly identify wheel flats and instantly check any questionable "rough ride" calls. The data can act as a decision support tool to enable infrastructure managers to quickly identify and eliminate any problem if necessary.

Train maintenance practices have taken great strides to become more efficient and more reliable in recent years. Perpetuum's wireless condition monitoring technology seeks to support this by providing a solution that makes asset failures easier to manage and predict. With no wires, batteries and maintenance required, data sent directly to PCs, tablets or mobiles is configurable to the users' exact needs. In addition, once the data is assimilated into future planning, repair and buying decisions, it is possible to dramatically reduce operational and maintenance costs, as operators in Britain, Sweden and Australia are already experiencing.