The two parallel outdoor penstocks of Perebella – Rosone are located near the “Parco Nazionale del Gran Paradiso” in Piemonte, Italy.
The manager of the hydro power plant, IREN Energia of IREN Group, decided to install a fiber optic monitoring system to control the behavior of six joints.
The scope of the SHM system is to measure relative movements between two sections across a joint. The two penstocks are parallel and the 3×2 monitored joints are located at about 50m, 100m and 250m from the upstream reservoir.
The monitoring system is composed of three consecutive chains of six deformation and six temperature sensors each, so thirty-six sensors in total.
Every joint is composed of three deformation and three temperature sensors, positioned at three, at nine and at twelve o’clock.
Near the instrumented sections, there are three junction boxes connected to each other by a multi-fiber cable starting at the control room.
All 36 sensors are measured automatically and concurrently; the provided SDB software allows having real time data visualization, pre-warning and warning alert levels and graphic and table history display over a selected period.
During the operation, the client estimated movements of about 1mm per year and they should be cumulative.
During the maintenance phase, when the penstock is empty, due to thermal expansion, the relative movements of two consecutive flanges can reach 1cm.
The MuST FBG deformation sensors are all 2m long with a measurement range of 1.25% of full scale, corresponding to 2.5 cm. Therefore, they are able to measure the deformations in all working conditions for a long time without any adjustment.