Author: Lee, Kar-yun
Title: Exploration of using fibre bragg grating technology in railway engineering
Degree: Eng.D.
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations
Railroad engineering
Optical fiber detectors
Department: Department of Electrical Engineering
Pages: 1 v. (various pagings) : ill. ; 30 cm.
Language: English
Abstract: The Kowloon Canton Railway Corporation KCRC encountered a serious electromagnetic interference problem to its signaling equipment in the course of trial operation of the newly commissioned commuter railway line. The data communication used twisted pair copper wires for transmission and it picked up the electromagnetic interference of the 25kV power system and caused data corruption. The spectrum analysis of the electrical noise confirmed that it was originated from the traction current and the noise was picked up via inductive coupling. After implementing a number of remedial measures for the system, the data integrity was assured even it is still using copper wire for transmission, but occasionally, data disturbance still happens. To totally eliminate the disturbances, optical fibre data transmission was explored but it is costly for retrospectively fitting. Apart from having the beauty of EMI free characteristics, optical systems can be considered as a strong contender to conventional signal equipment and it is highly feasible to build a virtual optical signal system on top of the existing one as a back up in the short term. In a longer term one could replace the conventional electrical signal systems with their optical counterparts. In recent years, Fibre Bragg Grating (FBG) sensors are finding increasing applications in smart structures. They can be embedded in civil structures such as bridges, buildings etc for the detection and monitoring of parameters such as strain, pressure and temperature. It allows the user to carry out assessments on the integrity of structures at various manufacturing and construction stages, and facilitates health management of many important structures in their subsequent operations. However, the application of optical sensors in railway engineering is rare. The research is to explore the technical feasibility and potential usage of FBG sensor for railway application. The research comprised mainly of three stages. The first stage is to explore and confirm the integrity of the signals that could be obtained by embedding FBG sensors on train and on track. Subsequent to its confirmation, several potential applications of FBG sensors were studied in-depth by capturing substantial amount of mainline service field data in the second stage of the research work. The final stage of the research work is to analyze the field data and confirm the technical viability of the FBG sensors on various railway applications with suggestions on how they can be implemented in future. The research reveals that FBG could be used to replace conventional sensors of the axle counter system in signaling engineering, for the derailment detector in monitoring the train running safety when the train is negotiating with track curves & twist, for stress/strain monitoring of car structure by maintainer, for traffic flow monitoring by operators particularly on train load and speed etc.
Axle counter system is used for counting the number of train axles coming in and out of a section of rail track. The field tests carried out has concluded that FBG has great potential for replacing conventional railway axle counter system, which is based on the principles of magnetic field disturbance technology as the wheels are passing by. One of the most important safety assessments for running train on rail is on the risk of derailment, particularly for train wheels in negotiating curve and track twist. Derailment caused by track twist is related to a combination of the horizontal guiding force and the reduction of the vertical wheel-load of the leading wheel, i.e. off-loading of wheels. Field-testing result indicates that it is technically viable to mount the FBG sensors on critical track twist areas for real-time checking on the interaction of the track and vehicle to promptly assess the potential risk of vehicle from being off-loaded, i.e. the assessment of the derailment risk. In assessing the residual life of the train body mechanical structure, its loading duty, i.e. the stress and strain of the structure is required to be monitored. Because the accuracy of conventional strain gauges operating in hostile EMI conditions is seriously compromised, FBG sensor is found to be more suitable, as confirmed by successful field test results, for monitoring the stress/strain of the car body shell. Hence FBG sensors can be an as good, if not better, alternative to conventional strain gauge. By combining the capability of FBG sensors for axle counter application, for car loading and car body stress/strain monitoring, it is found to be feasible to further develop and use these optical sensors for train identification, train speed detection, car loading monitoring and train traffic flow. FBG axle counter, derailment detector and stress/strain monitoring device have lots of advantages over their conventional counterparts using strain gauge due to its electrical immunity to noise, multiplexing capability, compactness and more importantly, it's relatively low cost of construction. Given there is a weather proof and robust mounting methodology being identified in the next phase, the FBG sensors will become a strong competitor to conventional sensors in a number of applications in railway engineering. Once the safety, reliability and integrity of FBG systems is proven to be satisfactory, one can exploit the full potential of these optical sensors to build a smart & safe railway.
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