Section: New Results

Fault detection and localization in networks of transmission lines

Participants : Mohamed Oumri, Michel Sorine.

Some results have been obtained in collaboration with Florent Loete (LGEP) and Qinghua Zhang (Inria, I4S):

- Experimental validation of the inverse scattering method for distributed characteristic impedance estimation. Our theoretic results and numerical simulations have shown the ability of inverse scattering-based methods to diagnose soft faults in electric cables, in particular, faults implying smooth spatial variations of cable characteristic parameters. We have obtained laboratory experiments confirming the ability of the inverse scattering method for retrieving spatially distributed characteristic impedance from reflectometry measurements. Various smooth or stepped spatial variations of characteristic impedance profiles have been tested. The tested electric cables are CAN unshielded twisted pairs used in trucks and coaxial cables [37] .

- Diagnosis of networks using tagged electric lines. A new electromagnetic marking method of transmission lines has been proposed for diagnosis of electric networks when conditions of uniqueness of the solution are not fulfilled (e.g. in case of symmetries): small non-interfering characteristic defaults are added to the lines and used as tags. A patent application has been submitted [36] .

A new application of our monitoring technique has been explored in collaboration with EDF and a first result has been obtained:

- Monitoring of post-tensioned ducts or water content in concrete walls with embedded transmission lines. We have presented an electromagnetic method of diagnosis based on frequency domain reflectometry (FDR) associated with our inversion algorithm, ISTL (Inverse Scattering for Transmission Lines). ISTL allows one to estimate the spatial profile of the electrical impedance of the line from the FDR measurements. Experimental results on two mockups of external post-tensioned ducts with filling defects show the feasibility of the method. We will try to show the similarities between auscultation external post-tensioned ducts and measurement of water content by TDR probes (Time Domain Reflectometry) [34] .

- Fault diagnosis of wired electric networks by reflectometry. A first extension to Baum-Liu-Tesche equations has been proposed in [31] .