Monitoring & metering

Predictive maintenance of rail traction motors using depot-based vibration monitoring

In this article, Ian Pledger, service engineer at Schaeffler UK, describes the results of a series of studies involving depot-based condition monitoring of railway traction motors using underfloor wheel lathes. These studies have proved that simple vibration-based parameters are often sufficient in providing very reliable indications of motor condition

equipment condition onboard the train as it operates in-service, in order to predict which parts are likely to fail and when. In this way, maintenance can be planned and there is an opportunity to change only those parts that are showing signs of deterioration or damage. Problems can be detected in advance and maintenance is performed only when needed. However, while the use of RCM is receiving


much attention, Schaeffler UK has investigated whether depot-based vibration measurements, using an underfloor wheel lathe to rotate the wheelset, could be used to assess the condition of the traction motor and gearbox. Working closely with different fleet operators, Schaeffler adopted this unique approach by using vibration measurements to assess the condition of traction motors without the need to remove equipment from the bogie. Six studies were undertaken on high-speed passenger trains involving a wide range of traction motor makes and sizes, from 8MW high speed trains down to light rail-vehicles. Each study identified potential failures of bearings

in traction motors early, thus avoiding any catastrophic failures or repairs. Potential failures were identified on ball bearing and cylindrical roller bearing components such as inner and outer ring raceways, cages and rolling elements. These signs of localised damage (and widespread damage in some cases) appeared in many forms including abrasive wear, adhesive wear, spalling, fatigue, corrosion, fretting, cracks, indentations, discolouration, false brinelling and degradation/starvation of grease. In other cases, electrical erosion, high axial loads

ail operators are increasingly adopting remote condition monitoring (RCM) to monitor railway assets, including

and contamination were found to be the primary causes of bearing damage. In addition, it was discovered that some of the traction motors in the studies had been fitted with non-premium bearing brands, which although may have seemed attractive at the time from a purchasing viewpoint, the performance and reliability were seriously compromised and resulted in a shortened service life, premature failure and significantly higher operating costs. The studies provided valuable information to

fleet operators about the condition of bearings and other rotating components on traction motors. If left undetected, these worn or damaged components may have resulted in catastrophic failures of traction motors, with possible disruption to operation in service.

HandHeld vIbraTIon monITor deTecTS early SIgnS of damage Using the Detector III handheld vibration monitoring system from Schaeffler, engineers at a UK-based fleet maintenance depot could check train traction motors for early signs of damage to the bearings. The two handheld Detector III vibration

monitoring systems were supplied by Schaeffler UK and paid for themselves within just two months, by minimising disruption costs to rail operators and by significantly reducing the number of traction motor repairs due to bearing deterioration. Prior to investing in the Detector III handheld vibration monitors, the depot had been


experiencing bearing deterioration problems on some traction motors, which are fitted to the electrical multiple units. The bogies on these trains are all driven by the same traction motor. What the depot’s maintenance engineers needed was some method of monitoring the condition of the traction motor bearings in order to predict their remaining operational life and to take the appropriate corrective action before damage is caused to the motor. The traction motors have a service life

approaching one million miles before they need overhauling, but the depot had been experiencing some bearing issues earlier than this. After discussing these issues with Schaeffler UK, the customer invited Schaeffler to carry out a comprehensive program of measuring vibration on a number of traction motors. This involved measuring vibration on the traction motor housing and assessing the condition of the bearings and other associated mechanical components. The measurements were carried out whilst the

trains were positioned over an underfloor wheel lathe at one of the customer’s rail maintenance workshops in the UK. These wheel lathes are used to perform routine wheelset skimming in order to maintain the correct tread profiles.

relIable IndIcaTIon of moTor condITIon After carrying out detailed vibration measurements on the traction motor housing, it became apparent to engineers at Schaeffler that simple characteristic

April 2019 Instrumentation Monthly

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