Fault detection and location on rail systems

Rail infrastructure companies face numerous challenges in maintaining full operational status throughout their networks. Achieving maximum service availability for train operators while ensuring passenger safety, is central to the design and maintenance of the infrastructure. Maintaining traction and signalling systems and the power networks that supply them, are core to achieving this both in terms of user satisfaction and
economic impact.

LiveWire Innovation has developed a new approach for detecting and locating faults within live rail infrastructure and systems using a unique combination of cellular technology (Spread Spectrum) and cable test technology (Time Domain Reflectometry), resulting in what is referred to as SSTDR.

Rail applications face structural degradation of cables, malfunction of system elements such as switches and physical damage from construction and track repairs.

The network infrastructure that provides power for both traction and signalling, suffers from a variety of problems. Maintaining a state of good repair is a constant battle.  The issues faced include structural degradation of cables, malfunction of system elements such as switches and physical damage from construction and track repairs. Due to the substantial and high quality copper cables that are employed for this critical network, theft is also an issue, though has diminished for the time being with the drop in the price of copper.


To try and address the issues, rail infrastructure operators have deployed various systems to reroute power upon loss of supply and monitor for fault conditions such as ground faults and power loss.  Ageing and degradation of supply cables represent a significant challenge for many operators.   A number of major manufacturers have developed enhancements in their technology that monitor for changes in the physical state of cable insulation; improvements that are being evaluated by network operators. The capability to detect the gradual degradation of insulation that leads to sustained cable faults is an important tool in establishing network health.  Key problems remain though. Locating the sustained faults that result from physical events and cable degradation on an operational (live) network, remains an issue.  The detection and locating of intermittent faults that occur while the network is in operation is also a problem, as it is for live circuits in many applications.

Intermittent operational circuit faults in such environments are notoriously difficult to find.  In both fixed wing and rotor aircraft, faults reported in flight are often reported as no fault found (NFF) when post flight testing is performed.  The vibration, temperature changes and possibly moisture are not present after the flight, so the fault does not reoccur and is difficult to replicate.  Even if these faults do reappear, they are difficult to locate since they only appear while the cables are live, which to date has meant they could not be monitored.

Such faults occur in all electrical networks to various degrees.  Rail is a harsh environment, both trackside and within rolling stock/vehicles.  The traction and signalling networks are exposed to all weathers, substantial intermittent vibration and frequent physical changes.  These environmental and physical factors often change the electrical (impedance) characteristics of the cables and connector systems that make up the infrastructure, causing faults such as open circuits to occur for short periods or indeed, intermittently.  As well as being difficult to detect, finding the location of these faults takes substantial time and effort; leading to extended service outage periods and higher costs.  In addition, intermittent faults in the power networks put substantial strain on the equipment they supply, leading to premature aging and failure of the complex hardware
they supply.


A monitoring and sensing solution to this intractable issue has been developed within aerospace.

To ‘look into’ cabling infrastructure while it is in operation, requires the monitoring system to be able to sense faults while power and/or communications are present, without interfering with the operation of the system being monitored.   This has been achieved using a combined solution comprised of a technique called Spread Spectrum and Time Domain Reflectometry (TDR) technology.

Spread Spectrum has been better known within the wireless world, being used for control signalling within cellular networks. Using Spread Spectrum, wireless networks are controlled without the signalling interfering with the operation or quality of services.  When applied to wired infrastructure in combination with TDR technology, the same benefits are delivered, enabling systems to operate without interference while being monitored for intermittent and hard faults; the type of faults that interrupt rail services on a regular basis.  The combination of Spread Spectrum and TDR technology has been termed SSTDR.

SSTDR can be applied to a number of rail infrastructure issues, where the capability to detect and locate faults quickly and cost effectively can reduce fix times and enable timely maintenance.

Traction power cables are substantial and can be an attractive target for thieves.  These cables are also exposed to ageing environmental factors, which can result in insulation degradation and cracking, the latter often leading to intermittent shorts (faults) when exposed to moisture.   Detecting and locating these faults for the fastest possible fix can avoid service downtime during busy traffic periods.

The benefits are similar for the signalling infrastructure.  The sustained and intermittent faults that develop can be seen and located. Significant insulation degradation that is sensed by monitoring equipment at a supply point, can be investigated by utilising SSTDR’s capability to ‘look into’ the cable infrastructure to locate critical impedance changes that have developed in the cable.  Due to the core sizes and the copper quality, these cables can also be a specific theft target.  As with detection of both hard and intermittent faults, removal or cutting of such cables can be detected and located immediately. To date, the monitoring solutions available have not been able to reliably detect and locate intermittent events. The capability to do so can substantially enhance availability when applied to the signalling network.

Application of SSTDR monitoring to trackside systems has shown that previously undetected and difficult to locate infrastructure faults can be found quickly and effectively.  All cabling systems can suffer from various fault types; the severity and frequency depending on the installed environment, their use and the physical characteristics of the materials employed. Now SSTDR has started to prove its worth trackside, other applications such as cabling reliability issues within the trains that run on the networks can be investigated.  If this new approach can also deliver fast turnaround of fault detection and location on complex rolling stock, instances of journey delays due to these common but difficult to find faults should be a rare event.

Embedded Solutions

LiveWire’s sensor ‘engines’ in the form of fully engineered, credit-card sized printed circuit boards and multi-board stacks, as well as SSTDR chip-sets with corresponding reference designs for very high-volume applications.

LiveWire can work with most communications and control options.  Update and reporting interfaces that can be used include serial, USB, JTAG, Ethernet and others. Board-level solutions can support several other communications protocols including, SPI, I2C and CAN.

Handheld Solutions

Fully housed sensor modules for permanent installation. Handheld products using LiveWire’s Spread Spectrum brand of TDR for maintenance, field testing and electrical contractor markets.

The Mantis™ LW-MM200 is the first live cable tester module that monitors energized cable run faults and electrical circuits around-the-clock.

Fault Trapper monitors live circuits for intermittent conditions to record time and distance to Opens, Shorts and Arc Faults.

Dual mode TDR for testing and monitoring energized and unenergized systems.

Power Prowler

3-In-1 DMM/TDR Cable Fault Finder

FaultChaser Handheld

Fault Finding/Cable Length Measurement TDR