INTRO: Condition monitoring of a range of equipment on moving trains can lead to fewer delays, lower maintenance costs and smaller component stocks. The key is to marry detection equipment with automatic vehicle identification so that management knows precisely where and when to target resources
BYLINE: J J Marais Pr Eng
Senior Manager, Materials Engineering, Spoornet
TRAIN PERFORMANCE can be seriously affected by failing or malfunctioning components, with the consequences ranging from a minor delay to a serious and expensive derailment. Failed components or subsystems may also lead to damage of other equipment on the train, or to the track or infrastructure. The need to reduce costs in today’s competitive transport environment is increasingly important, and the opportunity to cut costs by monitoring the health of rolling stock is now opening up. It will also be possible to base maintenance requirements on the condition of critical components, so eliminating the need for costly time-based maintenance plans.
Spoornet has developed monitoring systems to detect malfunctioning or failing components on a train. Some of these operate automatically, alerting the section dispatcher in the control centre to an imminent failure. The CTC then instructs the train driver on procedures to follow, determined by the criticality of the failure.
Hot box detectors warning of overheated plain or roller bearings are currently used in conjunction with axle counters. The driver has to count the train axles to find the failing bearing, which often leads to errors and bearing failures in service.
A number of manual train condition monitoring systems have been developed, but these require the presence of trackside operators who feed data into a computer at specified measuring points. Interpretation of the results is slow and immediate reaction to problems very difficult. To identify the vehicle with the failing components, wagon and locomotive numbers are recorded on video. A time-consuming process then follows to match the recorded data with the vehicles.
For these reasons, manual measuring points are used on an irregular basis. The next step is to integrate and expand them to create an integrated train health monitoring system.
The positioning of a trackside measuring point should be carefully considered. In a typical situation wheel temperatures are measured at two locations, for example on the uphill approach to a summit and at a point on the following descent. At Measuring Point One, all wheel temperatures should be low (slightly above ambient temperature) as brakes are not normally applied at this location. A wheel significantly hotter than the others will therefore indicate sticking brakes. Should the temperature of all the wheels on the same wagon be higher than other wheels in the train, the hand brake might not have been released on that wagon or its brakes may be malfunctioning.
At Measuring Point Two, on the descent, all wheels are expected to be hot in relation to ambient temperature as the brakes have been applied. Should a wheel be significantly colder than the others, it would mean that the brakes on that wagon are faulty.
The positioning of measuring points for other components also requires careful consideration. Measurement of the position of wheels on axles, to detect broken or shifted wheels, should be undertaken well ahead of points and crossings. Should a shifted wheel be detected, the driver must be notified at a point where the train can be stopped before the crossing and a possible derailment avoided.
The parameter to be measured at each point should be clearly defined. To facilitate computerised processing of data, a minimum range of factors should be specified. These are: