Analysis of variation of Brillouin and Rayleigh scattering coefficients with thermal strain in Landau-Placzek ratio based optical fiber distributed sensing for XLPE insulated power cables

Abstract

The optical fiber distributed sensing method based on Landau-Placzek Ratio (LPR), where Rayleigh and Brillouin scattering coefficients are utilized, is widely used for detecting thermal strain formations in XLPE insulated power cables. In this study, using strain dependence of material characteristics in XLPE cable insulation, i.e. Young and Shear moduli and the Poisson ratio, variations of Rayleigh and Brillouin scattering coefficients with thermal strain and their thermal strain sensitivities have been analyzed. Using Matlab R2008a, behaviour of the sensing fiber integrated to a 64/110 kV power cable has been obtained with simulations for 318°K-339°K temperature range and 668 με - 1231 με thermal strain range. For thermal strain variations in 668 με - 1231 με range, while thermal strain sensitivity of Rayleigh scattering coefficient is changing from 1.8286 × 10-4 % to 1.8267 × 10-4 %, that of Brillouin scattering coefficient changes from-7.9727 × 10-4 % to - 8.0086 × 10-4 %. Using simulation results, thermal strain sensitivity variations of Rayleigh and Brillouin scattering coefficients have been computed as ~ - 3.27 × 10-10 %/με and ~ - 6.38 × 10-9 %/με, respectively. In 668 με - 1231 με range, it has been observed that thermal strain sensitivity of LPR changes from 9.7439 × 10-4 % to 9.7068 × 10-4 %. Using LPR simulation results, strain-dependent LPR formula derived with the analytical method has been simplified and expressed with a linear equation.