Experiences with ampacity rating calculations for wind farm export cable

This paper addresses ampacity rating calculations using Finite Elements Analysis (FEA) compared to data from a Distributed Temperature Sensing (DTS) measurement system on an onshore wind farm export cable in operation. Steady-state and time-dependent rating calculations have been performed for several operational scenarios and input parameters, and compared to DTS data on the same cable. The results show that conventional steady-state calculations give a very conservative estimate of the current-carrying capacity. Statistical treatment of the intermittent load profile shows that the cable is subjected to the static load limit only at short periods of time. Additionally, the local ground temperature is below standard values. Time-dependent rating calculations identified different thermal time constants for the various sections of the cable length, proving to be more representative than steady-state calculations for cables subjected to intermittent loads. DTS measurements found certain unexpected thermal bottlenecks which will limit the cable ampacity. Although precise route surveys are always performed before cable installation, maps of underground infrastructure can be incomplete. DTS surveillance may thus be necessary for full exploitation of installed capacity. Inspec keywords: offshore installations; temperature sensors; power cables; finite element analysis; wind power plants Subjects: Wind power plants; Power cables; Thermal variables measurement