On-site testing of critical cable infra-structure

The resilience of distribution grids is strongly depending on the vulnerability of overhead lines to extreme weather conditions. A usual coping strategy is the conversion of overhead lines to cable connections. In the same way, already existing cable connections are facing increased load scenarios. Both scenarios support increasing numbers of cable installations and cable upgrades. Especially in the field of primary distribution systems, the availability of newly installed, upgraded and repaired cables needs to be guaranteed by on-site testing. It needs to differentiate between secondary medium voltage (MV) cables up to 36 kV and primary cables used for rated voltages above 36 kV up to 132 kV. Here, the enhanced utilization of the specific dielectric performance of the insulating material leads to stress levels which are no longer comparable to secondary MV cables and therefore with the electric field stress of high voltage cables. Consequently, the requirements of the standards IEC 63026 as well as IEC 60840 and 60502-2 shall be taken into consideration. Beside SOAK test, both standards require an onsite resonant testing for these cables. In addition to the dielectric test, the evaluation of partial discharges is recommended. As the effort for longer cables is high, non-conventional PD measurement techniques like TruePD are evaluated.