Improved cable RTTR and early failure detection by combining DTS monitoring with distributed point sensing

During 2022-2023, a 4.1 km, 66 kV subsea export cable from an onshore substation to a string of turbines was instrumented with both DTS along the cable, and FBG-based sensors monitoring phase current and temperature at the terminations at each end. This enabled comparisons between the temperatures recorded by both monitoring systems over a period of one year. This analysis includes assessments of the response of each system’s temperature measurements to fluctuations in phase current in the cable and ambient temperature. The results show that the location of the hottest temperatures along the cable will vary seasonally. Between mid-June and October, when ambient temperatures are higher, terminations are the hottest point in this system more frequently. This shows that termination temperature measurements are beneficial in supporting real-time thermal rating (RTTR), even for a healthy cable system in a relatively cold climate. Furthermore, the higher sampling rates and proximity to the termination with point temperature sensing using FBGs provides more accurate and rapid assessments of termination temperature responses to phase current loading.

This highlights the additional benefits from FBG monitoring for termination condition and cable health monitoring during the lifetime of the asset.