Development of optical fiber sensors applied to the high speed railway environment

Abstract

High speed railway is a fast and energy-efficient mode of transport in continuous growth that needs efficient control and security systems. In this work we present the results of field tests concerning the application of fiber optic sensors applied to the high speed trains infrastructure with the final aim of improving the current strategies of maintenance and increasing the safety level of the network. The intrinsic both electrical and magnetic insulation of the fiber optic makes it the ideal medium for this environment where electromagnetic interference reaches very high levels. Moreover the resistance to a wide range of temperature and to environmental corrosion of fiber optic together with a great sensor multiplexing capability and the low attenuation make railway fiber optic sensor application close to ideal. On one side we studied the application of Fiber Bragg Grating (FBG) sensors for the monitoring of railway infrastructure and the possibility to embed them in composite materials such as those used in the train wagon. We performed the monitoring of a rail track of the high speed line Madrid-Barcelona at KP 69.500, @(40.624358,-3.093255), where the trains are tested during commercial operation with maximum speeds between 250 and 300 km/h. The FBG sensor interrogation system used allows the simultaneous monitoring of four FBG sensors at 10 ksamples/s. We prove that the different position of the FBG sensors in relation with the rail can be used for different purposes such as train identification, axle counting (track circuit, for occupation checking of critical sections -such as tunnels-), speed and acceleration calculation (to optimize train scheduling), wheel imbalance detection (to reduce derailment risks), dynamic load calculation (for load estimation, to optimize train scheduling, for studying wear effects) and wheel imperfections monitoring (to minimize wear effects and derailment risks scheduling a wheel maintenance). A removable FBG-sensor device was also proposed to be rapidly mounted to the rail and, in any moment, moved to any other position along the line, capable, in this way, of reducing the costs of installation of fiber optic sensors. We show results about the real time structural monitoring, in the viaduct over the river Jarama located in the KP 23.609 @(40.401315,-3.506577) of the high-speed line Madrid-Barcelona, with the objective of demonstrating that FBG-sensors are capable to measure stress in complex structures and that are useful instruments to complete the monitoring for the train infrastructures. At the same time, we developed a polarimetric current sensor based on Faraday effect for the monitoring of catenary current in changeover sections. We used a low-cost all-fiber configuration that fulfils the requirements of light weight, robustness, sensitivity and accuracy desired for this application. The optical configuration is extremely simplified through the use of few cost-effective, all-fiber devices with a simplified alignment. It allows high sensitivity for low current values, demonstrating a resolution below the ampere level with a dynamic range up to $500\; A$. The setup is electronically self-referenced to reduce the effect of small misalignments in the polarization, power variations in the optical source, temperature changes, birefringence and bending-induced attenuation in the lead fiber. The field tests are performed in the high-speed line Madrid-Barcelona in Anchuelo in the KP 44.254 @(40.463383,-3.29556)) both during commercial operation and with test train simulating fault conditions. Key words: Optical fiber, Bragg gratings, FBG, Strain Sensor, Structural monitoring, High Speed Train, Composite material, Temperature Compensation, Weight-In-Motion, Dynamic Load, Comfort, wear, rail, out-of-roundness, wheel flat, wheel condition, wheel state, current sensor, polarimetric sensor, Faraday effect.