The impact of temperature and strain formations on young and shear moduli in usage of optical fiber distributed sensing for power cables

Abstract

In this study, a novel method that can be used for sensing temperature and strain changes simultaneously occurred along the XLPE insulated high voltage (HV) cables has been proposed. In this method, optical fiber distributed sensing principle based on the temperature dependence of Brillouin power changes and the temperature and intrinsic thermal strain dependencies of Young modulus and Shear modulus of the sensing fiber have been utilized. The cable model used in this study has been based on an XLPE insulated 89/154 kV power cable with a conductor cross-sectional area of 630 mm(2) and a length of 2 km, which has been laid under 1.5 m of a sandy ground of Bursa with an ambient temperature of 20 degrees C in July. The sensing fiber is a single mode fiber at 1550 nm. While temperature sensitivity of the Young modulus has been determined as -2.33 x 10(-6)%/degrees K in the operation temperature region of the power cable, that of the Shear modulus has been obtained as -6.67 x 10(-7)%/degrees K. Furthermore, strain sensitivities of Young and Shear moduli at the hottest point of the power cable have been obtained as 5.7154 x 10(-4)% and 3.0502 x 10(-4)%, respectively. In the operation regime of the cable, similar to 26.83 mu epsilon strain variation has been occurred for a 1 degrees K variation in the temperature along the cable. Both theoretical computations and simulation results show that it is a more efficient method to utilize strain and temperature sensitivities of the Young modulus in gathering information about the lifespan and the capacity of the power cable with respect to thats of the Shear modulus.