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International audience; Electrical arc faults that occur in photovoltaic systems represent a danger due to their economic impact on production and distribution. In this paper we propose a complete system, with focus on the methodology, that enables the detection and localization of the arc fault, by the use of an electromagnetic-acoustic sensing system. By exploiting the multiple emissions of the arc fault, in conjunction with a real-time detection signal processing method, we ensure accurate detection and localization. In its final form, this present work will present in greater detail the complete system, the methods employed, results and performance, alongside further works that will be carried on.

This work has been funded by the FUI Tenerrdis - Minalogic project “Smart Hydro Monitoring”; International audience; In this paper we present the result of our research concerning the improvement ofacoustic time of flight flow metering for water pipes. Current flow meters are based on theestimation of direct time of flight by matched filtering of the received and emitted signals byacoustic transducers. Currently, narrow band signals are used, as well as a single emitter/receptortransducer configuration. Although simple, this configuration presents a series of limitationssuch as energy losses due to pipe wall/water interface, pressure/flow transients, sensitivity toflow induced vibrations, acoustic beam deformations and shift due to changes in flow velocityand embedded turbulence in the flow. The errors associated with these limitations reduce theoverall robustness of existing flow meters, as well as the measured flow rate range and loweraccuracy. In order to overcome these limitations, two major innovations were implemented atthe signal processing level. The first one concerns the use of wide band signals that optimise thepower transfer throughout the acoustic path and also increase the number of velocity/flowreadings per second. Using wide band signals having a high duration-bandwidth productincreases the precision in terms of time of flight measurements and, in the same time, improvesthe system robustness. The second contribution consists in the use of a multiple emitter – multiple receivers configuration (for one path) in order to compensate the emitted acoustic beamshift, compensate the time of flight estimation errors and thus increase the flow meter’srobustness in case of undesired effects such as the “flow blow” and transient/rapid flowrate/velocity changes. Using a new signal processing algorithm that take advantage of thecontrolled wide band content coming from multiple receivers, the new flow meters achieves ahigher accuracy in terms of flow velocity over a wider velocity range than existing systems.Tests carried out on real scale experimental facility showed an increase in acoustic time of flightestimation, accuracy of 50% with respect to the existing measurements techniques based onlyon signal correlation.

Cavitation phenomena are known for their destructive capacity in hydraulic machineries and are caused by the pressure decrease followed by an implosion when the cavitation bubbles find an adverse pressure gradient. A helical vortex appears in the turbine diffuser cone at partial flow rate operation and can be cavitating in its core. Cavity volumes and vortex frequencies vary with the under-pressure level. If the vortex frequency comes close to one of the eigen frequencies of the turbine, a resonance phenomenon may occur, the unsteady fluctuations can be amplified and lead to important turbine and hydraulic circuit damage. Conventional cavitation vortex detection techniques are based on passive devices (pressure sensors or accelerometers). Limited sensor bandwidths and low frequency response limit the vortex detection and characterization information provided by the passive techniques. In order to go beyond these techniques and develop a new active one that will remove these drawbacks, previous work in the field has shown that techniques based on acoustic signals using adapted signal content to a particular hydraulic situation, can be more robust and accurate. The cavitation vortex effects in the water flow profile downstream hydraulic turbines runner are responsible for signal content modifications. Basic signal techniques use narrow band signals traveling inside the flow from an emitting transducer to a receiving one (active sensors). Emissions of wide band signals in the flow during the apparition and development of the vortex embeds changes in the received signals. Signal processing methods are used to estimate the cavitation apparition and evolution. Tests done in a reduced scale facility showed that due to the increasing flow rate, the signal -- vortex interaction is seen as modifications on the received signal's high order statistics and bandwidth. Wide band acoustic transducers have a higher dynamic range over mechanical elements; the system's reaction time is reduced, resulting in a faster detection of the unwanted effects. The paper will present an example of this new investigation technique on a vortex generator in the test facility that belongs to ICPE- CA.