Ferdinand Klug

Design and Calibration of a Fiber-Optic Monitoring System for the Determination of Segment Joint Movements Inside a Hydro Power Dam

In hydro power dams with arch dams as water storage, the movements of the concrete segment joints are monitored. New monitoring concepts are required as most dams were updated to more efficient pumped-storage power stations within the last years, which significantly changed the loading conditions. Inside one specific dam, the largest segment joint movements were up to 2.5 mm in the past. We developed a fiber Bragg grating (FBG)-based automatic monitoring system for the simultaneous measurement of concrete segment joints. Using our fiber-optic calibration facility, several commercial FBG-based strain transducers were tested. The facility and its capabilities are described. For the investigated sensors, nonlinearity and hysteresis effects of more than 20 μm/m were found, which is much more than expected. The results clearly show the need for standards in fiber-optic sensing where minimum requirements for sensor specifications should be defined. In an extended field trial, several appropriate sensors were installed in a hydro power dam. First results show an increased number of load cycles and smaller movements for the dam in pumping mode. With the new system, these small deformations can be detected, and it will be investigated in future how they contribute to the aging of the structure.

Fibre optic monitoring system for the determination of segment joint movements inside a hydro power dam

In recent years hydro power stations were rebuilt to more efficient pumped storage power stations. This changed the loading conditions and new monitoring concepts are required. We developed a FBG based automatic monitoring system for the simultaneous measurement of concrete segment joints. With a fibre optic testing facility sensor nonlinearity and hysteresis effects were investigated. Using selected sensors the requested accuracy of 0.02 mm for deformations up to 3 mm can be achieved. Several sensors were installed in a hydro power dam. First results show an increased number of load cycles and smaller movements for the dam in pumping mode.

Performance assessment of a fiber Bragg grating sensor network inside a hydro power dam using optical backscatter reflectometry

In recent years, many hydro power plants were modified to pump storage operation. This changes the loading conditions and new monitoring concepts are required. We developed a fiber Bragg grating based monitoring system which was installed inside a hydro power dam in 2013. This paper reports on detailed investigations of this network using an optical backscatter reflectometer, which allows distributed strain sensing with a very high spatial resolution up to millimeters. Therefore, an analysis of the strain profile between two anchoring points of a FBG sensor can be performed. In addition to distributed sensing, the different wavelengths of the FBGs are determined in the frequency domain to verify the results of a classical FBG interrogator. These comparisons and further laboratory studies prove the suitability of the fiber optic system and demonstrate that a detailed analysis of FBG networks using optical backscatter reflectometry can provide valuable insights.