Fiber Bragg grating monitors for thermal and stress of the composite insulators in transmission lines

Running composite insulators are prone to failure due to their harsh surrounding work environment, which directly affects the safe operation of transmission lines. This paper puts forward the method of using fiber Bragg grating(FBG) as the monitors to parameters correlated with thermal and stress of the composite insulators in transmission lines at working status. Firstly, monitoring points are found out by the mechanical test on composite insulator samples. Secondly, based on the monitoring theory, this paper introduces the feasibility design frame of the composite insulator with FBG implanted in the rod and the online monitor system. At last, it describes applications of this monitor system in the field of transmission lines.

Case studies of high-sensitivity monitoring of natural and engineered slopes

High-sensitivity monitoring solutions are crucial for early warning systems of earth structures. In this paper, we discuss the design and implementation of such systems for natural and engineered slopes using two case studies. At the Gradenbach Observatory, one key element of the monitoring system is a large fiber optic strain rosette embedded in the slope. We demonstrate that the strain rosette can depict landslide deformations much earlier than geodetic sensors like GPS or total stations and is therefore well suitable for an early warning system. In a second application we report the construction of a reinforced earth structure using geogrids. A distributed fiber optic measurement system was installed to measure the current operating grade of the geogrids within the earth structure. About 2 km of Brillouin sensing cables were installed in the project area. It is demonstrated that the developed monitoring system is well suited for assessing the current state of health of reinforced earth structures.

Deformation monitoring and remote analysis of ultra-deep underground space excavation

The development and utilization of urban underground space is producing many deep foundation pits.On-site monitoring is a key issue to ensure the safety of the foundation excavation,especially the monitoring of the lateral displacement of the structure.The ultra-deep circular foundation excavation project(58.65 m deep,the deepest foundation pit in Shanghai)in the test section of the Suzhou River deep tunnel is one of the most challenging engineering around the world.The distributed optical fiber monitoring technology of Brillouin optical frequency domain analysis(BOFDA)was employed to monitor the lateral displacement of the deep foundation.The monitoring process lasted for 14 months,and a total of 19 times of monitoring was carried out following the progress of the excavation of the foun-dation pit.This paper introduces the process,methods and precautions of optical fiber monitoring from early installation,equipment debugging to data acquisition,data processing and data analysis.By comparing the fiber monitoring data with the manual monitoring data,the deformation of the deep foundation excavation is analysed.The analysis results not only obtain the deformation law of ultra-deep foundation excavation,but also prove the advantages of optical fiber monitoring in deep foundation excavation.Finally,with the support of the Smart Infrastructure Service System(iS3),the research combines optical fiber monitoring with an information platform.Under the framework of the iS3 platform,an integrated data processing and analysis module for fiber monitoring is developed,and the feasibility of remote real-time collection and analysis of monitoring data is discussed.With the support of the information platform,the monitoring data can be transmitted back to the computer terminal to realize remote monitoring.

Hybrid fiber Bragg grating sensor for vibration and temperature monitoring of a train bearing

We report a fiber Bragg grating（FBG）-based sensor for the simultaneous measurement of a train bearing’s vibration and temperature. A pre-stretched optical fiber with an FBG and a mass is designed for axial vibration sensing. Another multiplexed FBG is embedded in a selected copper-based alloy with a high thermal expansion to detect temperature. Experiments show that the sensor possesses a high resonant frequency of 970 Hz, an acceleration sensitivity of 27.28 pm/g, and a high temperature sensitivity of 35.165 pm/℃. A resonant excitation test is also carried out that demonstrates the robustness and reliability of the sensor.

Development of Ribbon Fiber Type Multi-Channel Power Level Monitor with Low-Insertion/Polarization Loss

We would like to propose a new in-line multi-channel power level monitor, which is applicable as tap-monitor for multi-channel WDM signals. Its ribbon fiber structure has far exceeded PLC performance and realized compact-size and lower insertion/polarization dependent loss.