Measurement Method for Temperature Sensitivity Coefficient of Embedded Optical Fiber in High-voltage XLPE Cable—Shorter Than Spatial Resolution of BOTDR

Temperature sensitivity coefficient of optical fiber is a critical parameter for distributed temperature measurement based on Brillouin scattering. However, the optical fiber required by traditional coefficient measurement method, is so long that it is not suitable for embedded optical fiber in high-voltage (HV) cross-linked polyethylene (XLPE) power cables. In this paper, a measuring system for temperature sensitivity coefficient of distributed Brillouin scattering optical fiber is established. By modulating the temperature of a short section of optical fiber to be remarkably differ from that of remaining optical fiber within the spatial resolution of sensing system, the coefficient can be obtained through measuring the Brillouin frequency shift (BFS) of the modulated peak in Brillouin gain spectrum (BGS). The results show that using Brillouin optical time domain reflectometer (BOTDR) with a spatial resolution of 10 m, the coefficient obtained by optical fiber longer than 0.5 m is the same as that obtained by 10 m optical fiber. As the phenomenon that the temperature sensitivity coefficient of polyvinyl chloride (PVC) jacketed optical fiber in the water blocking tape and power cable are both 1.4 MHz/°C, the embedded optical fiber in tape can be used to replace that in HV XLPE cable to measure the coefficient.